,transcriber ,note ,text emphasis is denoted as ,italics4 ,,united ,,states ,,department ,,of ,,agriculture ,,bulletin ,no4 #hdd ,contribution from the ,bureau of ,plant ,industry ,,wm4 ,a4 ,,taylor1 ,chief ,washington1 ,d4 ,c4 ,,professional ,,paper ,august #aa1 #aibj ,,sweet-,,clover ,,seed ,part ,i4--,pollination ,studies of ,seed ,production ,part ,,ii4--,structure and ,chemical ,nature of the ,seed ,coat and its ,relation to ,impermeable ,seeds of ,sweet ,clover ,by ,h4 ,s4 ,,coe1 formerly ,assistant ,agronomist1 ,office of ,forage-,crop ,investigations1 and ,j4 ,n4 ,,martin1 ,professor of ,morphology and ,cytology1 ,iowa ,state ,college ,,contents ,page ,part ,i4--,pollination ,studies of ,seed ,production4 ,unsatisfactory yields of sweet-clover seed #a ,previous investigations of the pollination of sweet clover #b ,outline of pollinating experiments #c ,structure of the flowers of ,melilotus alba #d ,development of the floral organs of sweet clover #e ,fertilization in ,melilotus alba #h ,development of the seed #h ,mature pollen of sweet clover #i ,germination of the pollen #i ,cross-pollination and self-pollination of sweet clover #aj ,artificial manipulation of sweet-clover flowers #aj ,seed production of ,melilotus alba under ordinary field conditions #ac ,efficiency of certain kinds of insects as pollinators of sweet clover #ad ,relation of the position of the flowers on ,melilotus alba plants to seed production #ai ,influence of the weather at blossoming time upon seed production #bj ,insect pollinators of sweet clover #ba ,effect of moisture upon the production of ,melilotus alba seed #bb ,part ,,ii4--,structure and ,chemical ,nature of the ,seed ,coat and its ,relation to ,impermeable ,seeds of ,sweet ,clover4 ,historical summary #bf ,material and methods #cj ,structure of the seed coat #ca ,microchemistry of the seed coat #cc ,the seed coat in relation to the absorption of water #cd ,a comparison of permeable and impermeable seed coats #cd ,the action of sulphuric acid on the coats of impermeable seeds #ce ,literature ,cited #cf ,illustration ,,washington ,,government ,,printing ,,office #aibj ,,united ,,states ,,department ,,of ,,agriculture ,,bulletin ,no4 #hdd ,contribution from the ,bureau of ,plant ,industry ,,wm4 ,a4 ,,taylor1 ,chief ,washington1 ,d4 ,c4 ,,professional ,,paper ,august #aa1 #aibj ,,sweet-,,clover ,,seed ,part ,i4--,pollination ,studies of ,seed ,production ,part ,,ii4--,structure and ,chemical ,nature of the ,seed ,coat and its ,relation to ,impermeable ,seeds of ,sweet ,clover ,by ,h4 ,s4 ,coe1 formerly ,assistant ,agronomist1 ,office of ,forage-,crop ,investigations1 and ,j4 ,n4 ,martin1 ,professor of ,morphology and ,cytology1 ,iowa ,state ,college4 ,,contents ,page ,part ,i4--,pollination ,studies of ,seed ,production4 ,unsatisfactory yields of sweet-clover seed #a ,previous investigations of the pollination of sweet clover #b ,outline of pollinating experiments #c ,structure of the flowers of ,melilotus alba #d ,development of the floral organs of sweet clover #e ,fertilization in ,melilotus alba #h ,development of the seed #h ,mature pollen of sweet clover #i ,germination of the pollen #i ,cross-pollination and self-pollination of sweet clover #aj ,artificial manipulation of sweet-clover flowers #aj ,seed production of ,melilotus alba under ordinary field conditions #ac ,efficiency of certain kinds of insects as pollinators of sweet clover #ad ,relation of the position of the flowers on ,melilotus alba plants to seed production #ai ,influence of the weather at blossoming time upon seed production #bj ,insect pollinators of sweet clover #ba ,effect of moisture upon the production of ,melilotus alba seed #bb ,part ,,ii4--,structure and ,chemical ,nature of the ,seed ,coat and its ,relation to ,impermeable ,seeds of ,sweet ,clover4 ,historical summary #bf ,material and methods #cj ,structure of the seed coat #ca ,microchemistry of the seed coat #cc ,the seed coat in relation to the absorption of water #cd ,a comparison of permeable and impermeable seed coats #cd ,the action of sulphuric acid on the coats of impermeable seeds #ce ,literature ,cited #cf ,part ,i4--,,pollination ,,studies ,,of ,,seed ,,production4 ,,unsatisfactory ,,yields ,,of ,,sweet-,,clover ,,seed4 ,in some sections of the country much trouble has been experienced for a few years past in obtaining satisfactory yields of sweet-clover seed4 ,this difficulty has been due for the most part to the following causes3 7#a7 ,to cutting the plants at an improper stage of development1 7#b7 to the use of machinery not adapted to the handling of the crop1 7#c7 to the shedding of immature pods1 and 7#d7 possibly to the lack of pollination4 ,as the first two have been overcome1 mainly because of a better understanding of the requirements for handling this crop1 the subject matter of this bulletin is concerned primarily with the factors which produce the third and fourth causes4 ,where the production of seed was disappointing although the plants produced an abundance of flowers1 it has been observed that many apparently were not fertilized1 or if fertilized the pods aborted4 ,in order to obtain data in regard to the causes of the failure of sweet clover to produce a normal seed yield1 a study was made of the insects which were most active in pollinating the flowers1 the source of the pollen necessary to effect fertilization1 and the conditions under which the flowers must be pollinated in order to become fertilized4 ,the relation of environmental conditions to the shedding of immature pods was also investigated4 ,in order to overcome local environmental factors as much as possible1 the experiments were conducted on the ,government ,experiment ,farm at ,arlington1 ,va41 and in cooperation with the botanical department of the ,iowa ,state ,college at ,ames1 ,iowa4 ,,previous ,,investigations ,,of ,,the ,,pollination ,,of ,,sweet ,,clover4 ,since ,darwin 7#d1 p4 #cfj7a published the statement that a plant of ,melilotus officinalis protected from insect visitation produced but a very few seeds1 while an unprotected plant produced many1 other scientists have investigated this subject4 ,knuth 7#ai1 v4 #a1 p4 #cg71 in giving a list of the best known cases of self-sterility in plants1 mentions ,melilotus officinalis4 ,the same author 7#ai1 v4 #b1 p4 #bhb7 states that since the stigma projects beyond the anthers1 automatic self-pollination is difficult1 and for the same reasons ,mller 7#bi1 p4 #ahj7 believes that self-fertilization is not apt to occur4 #a ,the serial numbers in parentheses refer to ,literature cited1 pages #cf-ch4 ,in #aija ,kirchner 7#ah1 p4 #g7 covered a number of ,melilotus alba racemes with nets4 ,on one of the plants #ab protected racemes produced #ahg seeds and on another plant only one seed was obtained from #aj covered racemes4 ,this experiment was duplicated in #aijd1 with the result that #dj netted racemes produced an average of #ch seeds each4 ,kirchner concluded from this experiment that spontaneous self-pollination occurs regularly even though the stigma projects above the anthers4 ,he 7#ah1 p4 #h7 also performed an experiment with ,melilotus officinalis in #aija4 ,at this time #af isolated racemes produced a total of #aa seeds4 ,this experiment was repeated in #aijd1 with the result that #af protected racemes produced an average of #ad seeds each4 ,as the racemes on one of the plants that was protected in #aijd died1 ,kirchner concluded that the flowers of ,m4 officinalis were especially sensitive to inclosure in nets and that the failures to obtain more than a very few seeds on protected racemes in ,darwin's experiment and in his first experiment were due to this cause4 ,according to ,kerner 7#ag1 v4 #b1 p4 #cii7 the peas and lentils 7,pisum and ,ervum7 and the different species of horned clover and stone clover 7,lotus and ,melilotus7 as well as the numerous species of the genus ,trifolium and also many others produce seeds when insects are excluded from the plants1 and only isolated species of these genera gave poor yields without insect visitation4 ,,outline ,,of ,,pollinating ,,experiments4 ,the yield of sweet-clover seed varies greatly from year to year in many parts of the ,united ,states4 ,it has been assumed that this variation was due to climatic conditions1 as excellent seed crops were seldom harvested in seasons of excessive rainfall or of prolonged drought just preceding or during the flowering period4 ,the lack of a sufficient number of suitable pollinating insects also was thought to be an important factor in reducing seed production4 ,this was especially true where the acreage of sweet clover was large and where few1 if any1 honeybees were kept4 ,in order to obtain data upon the factors influencing the yield of seed1 a series of experiments was outlined to determine 7#a7 whether the flowers are able to set seed without the assistance of outside agencies1 7#b7 whether cross-pollination is necessary1 7#c7 the different kinds of insects which are active agents in pollinating sweet clover1 and 7#d7 whether a relation exists between the quantity of moisture in the soil and the production of seed4 ,the racemes containing the flowers which were to be pollinated by hand were covered with tarlatan before any of the flowers opened and were kept covered except while being pollinated until the seeds were nearly mature4 ,this cloth has about twice as many meshes to the linear inch as ordinary mosquito netting and served to exclude all insects that are able to pollinate the flowers4 ,when entire plants were to be protected from all outside agencies1 cages covered with cheesecloth1 glass frames1 or wire netting were used4 ,a preliminary study of the pollination of ,melilotus alba and ,m4 officinalis showed that both were visited by the same kinds of insects and that both required the same methods of pollination in order to set seed4 ,on this account ,m4 alba was used in most of the experiments reported in this bulletin4 ,where ,m4 officinalis was employed it is so stated4 ,,structure ,,of ,,the ,,flowers ,,of ,,melilotus ,,alba4 ,illustration3 ,fig4 #a4--;,different parts of the flower of ,melilotus alba3 #a1 ,side view of the flower2 #b1 side view of the flower with the carina and al slightly depressed2 #c1 side view of the flower1 showing the carina and al depressed sufficiently to expose the staminal tube and the tenth free stamen2 #d1 ala2 #e1 ate and carina spread apart to show their relative position and shape2 #f1 flower after the petals have been removed1 showing in detail the calyx and staminal tube2 #g1 the staminal tube split open to show the relative size and position of the pistil1 a1 ,al2 b1 vexillum2 c1 carina2 d1 calyx2 c1 stigma2 b1 anthers3 g1 tenth free stamen2 h1 digitate process of the superior basal angle of an ala2 i1 depressions in the ala2 j1 staminal tube2 k1 pistil4 ,the racemes of ,melilotus alba contain from #aj to #abj flowers with an average of approximately #ej per raceme for all of the racemes of a plant growing under cultivation in a field containing a good stand4 ,the flower consists of a green1 smooth1 or slightly pubescent calyx with #e-pointed lobes and with an irregular white corolla of five petals4 7,fig4 #a47 ,the claws of the petals are not united nor are they attached to the staminal tube which is formed by the union of the filaments of the nine inferior stamens4 ,as the claws of the al and carina are not attacked to the staminal tube2 the petals may be bent downward sufficiently far so that many different kinds of insects may secure without difficulty the nectar secreted around the base of the ovary4 ,the fingerlike processes of the al are appressed closely to the carina1 therefore the al are bent downward with the carina by insects4 ,these processes grasp the staminal tube superiorly and tightly when the carina and al are in their natural positions1 but when the carina is pressed downward by insects the fingerlike processes open slightly but not so far that they do not spring back to their original position when the pressure is removed4 ,the staminal tube splits superiorly to admit the tenth free stamen4 ,the filament of this superior stamen lies along the side of this staminal tube4 ,the filaments of the nine stamens which compose the staminal tube separate in the hollow of the carina4 ,all stamens bear fertile anthers4 ,the pistil is in the staminal tube1 the upper part of the style and stigma of which is inclosed with the anthers in the carina4 ,the stigma is slightly above the stamens4 ,an insect inserts its head into a sweet-clover flower between the vexillum and carina1 the stigma1 therefore1 comes into direct contact with the head of the insect and cross-pollination is effected4 ,at the same time the anthers brush against the insect1 so that its head is dusted with pollen1 to be carried to other flowers4 ,,development ,,of ,,the ,,floral ,,organs ,,of ,,sweet ,,clover4 ,illustration3 ,fig4 #b4--,lengthwise sectional view of a very young flower of ,melilotus alba1 showing the relative development of the stamens and pistil4 ,in the upper set of stamens the divisions of the mother cells are completed1 while division is just beginning in the lower set of stamens4 ,in the ovules the outer integuments are well started on their development1 a1 ,anther2 o1 ovule2 p1 pistil4 #ch4 ,the stamens of ,melilotus alba and ,m4 officinalis may be divided into two sets1 according to their length and time of development4 7,fig4 #b47 ,the longer set extends about the length of the anthers above the shorter set1 and the pollen mother cells in the longer set divide to form pollen grains at least two days earlier than those in the shorter set4 ,at the time the pollen mother cells divide1 the longer set of stamens is approximately three-eighths of a millimeter in length and the pistil about half a millimeter long4 ,the stigma and a portion of the style project beyond the stamens1 and this relative position is maintained to maturity4 ,the pollen mother cells undergo the reduction division while the megaspore mother cells are just being differentiated and while the outer integuments are barely prominent at the base of the nucellus4 ,the pollen grains are formed while the embryo sac is beginning to develop4 ,the division of the megaspore mother cell does not occur until a number of days later1 and the embryo sac is not mature until the flower is nearly ready to open4 ,thus1 the pollen grains are formed a week to #aj days before the embryo sac is ready for fertilization4 ,the pollen grains increase in size and undergo internal changes after their formation4 ,these changes1 which are not completed until the flower is one-half or more of its mature length1 may be regarded as the ripening processes1 and they are undoubtedly necessary before the pollen is capable of functioning4 ,for this reason it is probable that the pollen grains are not able to function much before the embryo sac is mature4 ,illustration3 ,fig4 #c4--,stigma at the time of pollination1 showing its papillate character and the position of the pollen in reference to the papill in pollination4 #age4 ,the pistils of ,melilotus alba and ,m4 officinalis are straight for the greater part of their length1 but curve rather abruptly toward the keel just below the capitate stigma4 ,the surface of the stigma is papillate4 7,fig4 #c47 ,in their reaction with ,sudan ,,iii1 alkanin1 and safranin the ,walls of the papill of the stigma show that some fatlike substances are present4 ,aside from water1 the contents of the papill consist chiefly of a fine emulsion of oil4 ,,development ,,of ,,the ,,ovules4 ,the number of ovules in the ovary of ,melilotus alba varies from two to five2 however1 most commonly1 three or four ovules occur4 ,in ,melilotus officinalis the number in each ovary ranges from three to six4 ,in both species the ovules are campylotropous at maturity with the micropylar end turned toward the base of the ovary4 ,mature ovules contain two integuments1 but the inner one does not close entirely around the end of the nucellus4 ,the outer integument develops considerably ahead of the inner one4 ,the outer integument is much thickened at the micropylar end1 the seed coat is formed from it1 and the inner integument is used as nourishment by the endosperm and embryo4 ,the number of megaspore mother cells in an ovule varies from one to many4 ,two or more embryo sacs often start to develop in the same ovule1 but seldom more than one matures4 7,pl4 ,i1 figs4 #a1 #b1 and #c47 ,in general1 the development of the embryo sac proceeds in the ordinary way1 as described by ,young 7#dd1 p4 #acc71 with the inner megaspore functioning4 7,text fig4 #d and ,pl4 ,,ii1 fig4 #a47 ,in its development the nucellus is destroyed rapidly1 the destruction being most rapid first at the micropylar end proceeding backward4 ,the nucellus is completely destroyed at the micropylar end by the time the embryo sac is mature1 and consequently the embryo sac comes in contact with the outer integument in this region4 7,pl4 ,,ii1 fig4 #a47 ,as the destruction of the nucellus extends toward the chalazal end the embryo sac becomes much elongated and tubelike4 ,the antipodals disappear early1 so that a mature embryo sac consists of the egg1 the synergids1 and the two polars4 ,the two polars lie in contact in the micropylar end of the sac near the egg until fertilization4 ,,sterility ,,of ,,the ,,ovules4 ,in ,melilotus alba and ,m4 officinalis there is very little tendency toward sterility of ovules4 ,in an extended study of ovules developing under normal and under excessive moisture conditions only an occasional one was found in which no reproductive cells were differentiated1 and no ovaries were found in which all of the ovules were sterile4 ,illustration3 ,fig4 #d4--,median section through an ovule1 showing the embryo sac with four nuclei and the position of the integuments4 #aej4 ,,development ,,of ,,the ,,pollen4 ,the pollen mother cells do not separate1 but previous to the reduction division the protoplasm shrinks from the walls1 thus forming a dense globular mass which often occupies less than half the lumen of the mother cell4 7,pl4 ,i1 fig4 #d47 ,nuclear division occurs while they are in this contracted condition1 and four nuclei are formed from two successive divisions4 ,the cytoplasm is equally distributed around each nucleus4 ,the four masses of protoplasm separate1 and as they enlarge a number of times and develop into mature pollen grains they become binucleate1 and a wall is gradually formed around each4 7,pl4 ,i1 figs4 #e and #f47 ,at first the cytoplasm is quite dense and contains some starch but no fatty oils4 ,however1 the cytoplasm of mature pollen grains is vacuolate1 and it contains a fatty oil in the form of an emulsion4 ,soon after the pollen grains are formed1 the walls of the mother cells disappear1 thus permitting the pollen grains to lie loose in the anther4 ,,fertilization ,,in ,,melilotus ,,alba4 ,the time intervening between pollination and fertilization was investigated with both self-pollinated and cross-pollinated flowers4 ,in cross-pollination the parents were separate plants4 ,this point was investigated with plants out of doors during the summer of #aiaf and with plants in the greenhouse during the following winter4 ,the time elapsing between pollination and fertilization ranged from #ej to #ee hours and was not longer in the case of self-pollinated than with cross-pollinated flowers4 ,furthermore1 the rate of the development of the embryo in each kind of pollination was studied and was found to be as rapid in self-pollination as in cross-pollination4 ,therefore1 self-pollination is apparently as effective as cross-pollination in ,melilotus alba so far as the vigor of pollen tubes and the rate at which embryos develop are concerned4 ,melilotus officinalis was not studied in reference to this point4 ,considerable difference often exists in the size of the young embryos in the ovules of the same pod4 ,this is due in part to a difference in the time of fertilization1 although some of it is due to a difference in nourishment4 ,it was observed that the ovule first fertilized might be an upper one1 lower one1 or any one between these4 ,occasionally one or more ovules are not fertilized4 ,,development ,,of ,,the ,,seed4 ,a proembryo with a rather long suspensor is developed from the fertilized egg4 7,pl4 ,,ii1 fig4 #b74 ,the endosperm1 which quite early forms a peripheral layer around the entire embryo sac1 develops most rapidly about the embryo1 which soon becomes thoroughly embedded in it4 7,pl4 ,,iii1 figs4 #a and #b47 ,after the embryo has used up the endosperm in the micropylar end and has enlarged so much as to occupy nearly all of the space in this region1 the development of the endosperm becomes more active in the chalazal end1 and when the embryo is mature there is very little endosperm left4 ,the seed coat begins to form about the time of fertilization1 although it apparently does not depend upon it1 for in ovules where fertilization is prevented the outer integument undergoes the early modifications in the development of the seed coat before the ovule breaks down4 ,the development of the seed coat is apparent first at the micropylar and chalazal ends1 where the outer cells of the outer integument become much elongated and their outer walls thicken very soon after fertilization4 ,the modifications in the development of the seed coat extend around the ovule from these points1 involving at first only the outer or epidermal layer of cells which form the malpighian layer4 ,later1 the cells just beneath the malpighian layer form the osteosclerid layer4 ,accompanying or closely following the formation of the osteosclerid cells1 the remaining cell layers of the outer integument become modified into the nutritive and aleurone layer1 and the seed coat is fully formed4 ,meantime the inner integument is practically all used as food4 ,plate ,i4 ,illustration ,development of the ,ovules and ,pollen in ,sweet ,clover4 ,fig4 #a4--,section through the nucellus of an ovule of ,melilotus alba1 showing two megaspore mother cells4 #cfj4 ,fig4 #b4--,median section through an ovule of ,melilotus alba1 showing the two cells resulting from the first division of the megaspore mother cell1 and the relative development of the different parts of the ovule4 #cjj4 ,fig4 #c4--,section through the nucellus of an ovule of ,melilotus alba1 showing two embryo sacs1 one being more advanced than the other4 #cfj4 ,fig4 #d4--,protoplasm of the pollen mother cell of ,melilotus alba contracted and ready to undergo division4 #efj4 ,fig4 #e4--,pollen grains of ,melilotus alba just formed1 showing their dense cytoplasm and the presence of the mother-cell wall4 #efj4 ,fig4 #f4--;a1 ,mature pollen grain of ,melilotus alba1 showing the binucleate condition at the time of shedding2 b1 surface view4 #efj4 ,plate ,,ii4 ,illustration ,fig4 #a4--,median ,section through an ,ovule of ,melilotus alba4 ,the embryo sac is shown ready for fertilization4 ,the egg and synergids are in contact with the outer integument at the micropylar end4 ,the remains of the antipodals may be seen at the chalazal end4 #ahj4 ,illustration ,fig4 #b4--,section through an ,ovule of ,melilotus alba1 about ,three ,days ,after ,fertilization4 ,the proembryo1 the endosperm1 and modifications of the integuments are shown4 ,at this stage the suspensor prominent part of the proembryo1 and the endosperm is most abundant around the embryo4 ,the inner integument is being rapidly destroyed1 and the outer integument is beginning to form the seed coat1 as is indicated by the modifications in the outer layer of its cells1 which are elongating and thickening their outer walls4 #cc4 ,plate ,,iii4 ,illustration ,fig4 #a4--,section of an ,ovule of ,melilotus alba after ,fertilization4 ,the stage of development is a little later than that shown in ,plate ,,ii1 figure #b4 ,the embryo is embedded deeply in endosperm tissue4 #de4 ,illustration ,fig4 #b4--,section through an ,ovule of ,melilotus alba after the ,embryo is ,nearly ,half ,mature4 ,but little endosperm remains except in the chalazal end1 and very little remains of either the nucellus or inner integument4 ,the modifications which transform the outer integument into a seed coat are well under way4 ,not only the outer layer of cells which becomes the ,malpighian layer is quite well modified1 but also the layer beneath is being transformed into the osteosclerid layer4 #cj4 ,plate ,,iv4 ,illustration ,stubble of ,melilotus alba4 ,these plants1 which were cut #ab inches above the ground during rainy weather1 had made a #dj to #db inch growth4 ,the stubble became infected at the top and the light-colored portions of them were killed by disease1 thus checking the water supply to the growing branches above the infection4 ,,mature ,,pollen ,,of ,,sweet ,,clover4 ,the pollen grains of ,melilotus alba and of ,m4 officinalis are quite similar4 ,each grain contains three germ pores1 and when viewed so that the pores are visible they present a slightly angled appearance4 ,the average dimensions of the pollen of ,melilotus alba and of ,m4 officinalis are #bf by #cb microns and #bd by #cj microns1 respectively1 when measured in the positions shown in b in ,plate ,i1 figure #f4 ,the walls of the pollen grains have cutin deposited in them1 as shown by their reactions with ,sudan ,,iii1 alkanin1 safranin1 and chloriodid of zinc4 ,the contents of the pollen grains give a distinct reaction when tested for fat1 and ,millon's reagent shows that also some protein is present4 ,tests for sugars and starch showed that these substances are not present in perceptible quantities in mature pollen grains1 although some starch is present in immature pollen4 ,,germination ,,of ,,the ,,pollen4 ,the germination of the pollen of ,melilotus alba permits considerable variation in moisture1 as is illustrated in ,table ,i4 ,table ,i4--,germination of the pollen of ,melilotus alba in water and in solutions of cane sugar of different strengths4 ---------------------------------------- ---------------------- ,cane sugar in solution 7per cent74 ,pure -------------------------------- ,melilotus alba4 water4 #h #ab #ah #bd #cj #ce #de #ee ---------------------------------------- --------------- ,germination of pollen #cc #bc #fd #df #fj #df #ca #bb #j per cent ---------------------------------------- --------------- ,the results given in ,table ,i represent the average of #ab tests4 ,some of the pollen grains burst in pure water and in the weak cane sugar solutions1 the percentage of bursting being greatest in pure water and decreasing as the percentage of sugar in the solution was increased4 ,there was considerable variation in the percentages of germination in both water and in the solutions of different strengths1 and at times there was very little bursting which was not accompanied by a high percentage of germination4 ,the pollen tubes grew as rapidly in water as in any of the sugar solutions1 some reaching a length of #ajj microns in six hours4 ,as the pollen tubes made no more growth in the solutions of sugar than in water1 it is evident that the sugar is not used as food1 but helps in germination by reducing the rate at which water is absorbed4 ,to judge from ,table ,i1 the pollen of sweet clover can be effective not only under ordinary conditions but also when the flowers are wet with rain or dew or when the stigma is so dry that in order to obtain water from the papill the pollen must overcome a high resistance offered by the sap of the papill1 a resistance that may be equal to the osmotic pressure of a #de per cent solution of cane sugar4 ,this is in accord with results obtained under field conditions2 as flowers that were pollinated while rain was falling set seed satisfactorily1 indicating that a high percentage of humidity in the atmosphere does not check the germination of the pollen sufficiently to interfere with fertilization4 ,neither was the setting of seed affected when the soil about the roots of plants was kept saturated with water1 showing that the excessive quantity of water in the stigmas resulting from an abundance of water in the soil did not interfere with the fertilization of the flowers4 ,no definite counts were made of the germination of the pollen of ,melilotus officinalis in the solutions of cane sugar of different strengths1 but observations show that the moisture requirement of the pollen of this species is approximately the same as that of ,melilotus alba4 ,,cross-,,pollination ,,and ,,self-,,pollination ,,of ,,sweet ,,clover4 ,results published by previous investigators on the cross-pollination and self-pollination of sweet clover do not agree4 ,the experiments of ,darwin 7#d7 show that the flowers are self-pollinated to only a small extent4 ,on the other hand1 ,kirchner 7#ah7 and ,kerner 7#ag7 find that self-pollination occurs generally and that cross-pollination is not necessary for the production of seed4 ,however1 all investigators agree that many different kinds of insects are able to pollinate sweet clover4 ,because of the diverse opinions as to the pollination of sweet clover1 a number of experiments were conducted to determine 7#a7 whether insect visitation was necessary to pollinate the flowers1 7#b7 if necessary1 whether the flowers must be cross-pollinated1 and 7#c7 what insects are active agents as pollinators of sweet clover4 ,,artificial ,,manipulation ,,of ,,sweet-,,clover ,,flowers4#b #b ,the writers wish to acknowledge their indebtedness to ,mr4 ,carl ,kurtzweil for assistance in conducting part of the field experiments at ,ames4 ,experiments were conducted to determine1 if possible1 the effect of various types of artificial manipulation of sweet-clover flowers when in full bloom on the production of seed4 ,only healthy1 vigorous plants growing on well-drained soil were selected for these experiments4 ,before any of the flowers were open1 the individual racemes were covered with tarlatan and labeled4 7,fig4 #e47 ,as soon as part of the flowers opened1 the racemes were uncovered and after removing all flowers that were not open the open flowers were pollinated and the racemes re-covered4 ,if the flowers of sweet clover are not fertilized they will remain open for two to three days1 then wither1 and in a short time drop4 ,but after being fertilized the ovules enlarge very rapidly1 and the corollas usually drop in about seven or eight days4 ,therefore1 all fertilized flowers can be distinguished a few days after fertilization has taken place4 ,counts were made of the number of pods which formed in #aj to #ab days after pollination4 ,an outline of the experiments is given in ,table ,,ii4 ,illustration3 ,fig4 #e4--;,individual racemes of white sweet clover covered with cheesecloth to protect them from insect visitation4 ,table ,,ii4--,treatment of sweet-clover flowers in the artificial-manipulation experiments4 ---------------------------------------- ----------------------------- ,experiment4 ,method of pollinating the flowers4 ---------------------------------------- ----------------------------- ,a ,check--covered4 ,b ,check--open to insect visitation at all times4 ,c ,a separate toothpick was used to spring the keel of each flower on the raceme4 ,d ,one toothpick was used to spring the keels of all the flowers on a raceme4 ,e ,cross-pollinated4 ,f ,raceme rolled several times between thumb and finger4 ---------------------------------------- ----------------------------- ,as insects1 and especially honeybees1 usually visit all recently opened flowers on a raceme1 experiments ,c and ,d were conducted to determine whether more seed would be produced when pollen from other flowers on the same raceme was placed on the stigmas of the flowers than when only the pollen produced by each flower was placed on its own stigma4 ,the effect of pollination when only the pollen produced by an individual flower was placed on its own stigmas was also obtained in experiment ,f1 as by this method of pollination no pollen was transferred from one flower to another4 ,it can not be stated definitely that the seed produced by the cross-pollinated flowers was the result of fertilization with foreign pollen1 as the anthers were not removed from the flowers pollinated because it would be necessary to remove the anthers when the flowers were not more than two-thirds mature1 and in doing this the flowers would be so mutilated that only occasionally would pollination at this time or at a later date be effective4 ,the flowers listed in experiment ,e were pollinated a short time before they opened1 and in each case pollen taken from flowers of other plants was placed on the stigmas4 ,the petals of the cross-pollinated flowers were not mutilated1 and in each case they returned to their original positions soon after pollination4 ,the results obtained in experiment ,b1 where the racemes were simply labeled and left open to the action of insects at all times1 serve for comparison with other experiments where the flowers were protected from insect visitation and were artificially manipulated4 ,martin 7#be7 found the setting of alfalfa seed and ,westgate 7#dj7 found the setting of red-clover seed to be affected by an excessive quantity of moisture in the soil or atmosphere4 ,in order to overcome the possible effect of this or of other detrimental factors1 in each experiment only the flowers on a certain number of racemes were pollinated at one time4 ,all of the experiments were repeated a number of times during the months of ,july and ,august1 #aiaf1 and the results given in ,table ,,iii show the total number of flowers pollinated and the number of pods that formed during the two months4 ,the results presented in ,table ,,iii show that flowers fertilized with pollen transferred from another plant produced a higher percentage of pods than any of the other treatments4 ,the results obtained in experiment ,d1 where the same toothpick was used to spring the keels of all the flowers on a raceme1 show that this method of pollination produced an average of #g4bd pods per raceme more than the racemes in experiment ,c4 where a separate toothpick was used for each flower4 ,these results indicate that pollen transferred from one flower to another on the same raceme is more effective than when the pollen produced by an individual flower is used to fertilize its own stigma4 ,however1 the results of experiment ,c prove that self-pollination is effective in ,melilotus alba4 ,in experiment ,b4 which was the open check1 #d4c per cent more flowers set seed than on the racemes where the same toothpick was used to spring all the keels1 but #aa4eg per cent more seed was obtained than in experiment ,c4 ,spontaneous self-pollination occurs to only a very small extent1 as will be seen from the results of experiment ,a1 in which an average of only #b4i per cent of the flowers set seed4 ,table ,,iii4--,effect of different types of artificial manipulation on the seed production of sweet clover at ,arlington1 ,va41 and at ,ames1 ,iowa1 in #aiaf4 ---------------------------------------- ------------------------ ,total number of-- ,flowers that set seed 7per cent74 ,experi--------------------------------- ----------- ,location4 ment4 ,racemes4,flowers4,pods set4 ,at each station4 ,average4 ---------------------------------------- --------------------- ,arlington ,a #di #c1eaj #add #d4a #b4i ,ames ,a #hd #d1ecf #ib #b4j ,arlington ,b #ajj #e1eii #c1igc #gj4ie #ff4ea ,ames ,b #aif #a1bgf #fjj #dg4jb ,arlington ,c #ej #a1bbi #gja #eg4jc #ed4id ,ames ,c #ge #bhi #acc #df4jb ,arlington ,d #ej #a1dhj #icf #fc4bd #fb4ah ,ames ,d #hh #ege #cdb #ei4dg ,arlington ,e #ca #cgg #cjg #ha4dc #gj4aj ,ames ,e #dh #age #hj #de4ga ,arlington ,f #cj #icc #ebd #ef4af 444444444 ---------------------------------------- --------------------- ,,seed ,,production ,,of ,,melilotus ,,alba ,,under ,,ordinary ,,field ,,conditions4 ,the production of seed of ,melilotus alba under ordinary field conditions varies considerably1 not only in different parts of the country but also on different fields in the same region4 ,a number of factors contribute to this variation1 one of the most important of which appears to be the inability of the plant to supply all the developing seed with sufficient moisture1 causing some of them to abort4 ,as pointed out on page #bb this condition was very marked in certain parts of the country in #aiaf4 ,however1 poor seed production is not always correlated with lack of moisture1 for the seed crop was a failure in #aiae1 where cloudy and rainy weather prevailed much of the time the plants were in bloom4 ,it is believed that the lack of pollination by insects was the principal cause for the failure of seed to set1 as very few insects visit sweet-clover flowers when such conditions prevail4 ,as sweet-clover pollen will germinate in pure water and as plants which have their roots submerged in water set seed abundantly when pollinated1 the failure of the seed crop in #aiae was not due to excessive moisture4 ,as a rule1 thin stands of sweet clover produce more seed to the acre than thick stands and isolated plants more seed than those growing in either a thick or thin stand4 ,the correlation of seed production with the thickness of stand is probably due to the shading and partial prevention of insect visitation to part of the racemes on the lower branches4 ,most of the flowers upon the lower branches of isolated plants are directly exposed to sunlight and to insect visits3 therefore the racemes on these branches produce as large a percentage of seed as the racemes on the upper branches4 ,in a thick stand1 little seed is produced by racemes on the lower branches4 ,a plant approximately #c feet high growing close to the center of a field at ,arlington4 ,va41 in which was an average stand of four sweet-clover plants to the square foot was selected in order to determine the number of racemes produced and the average number of seeds to the raceme4 ,this plant produced #aif racemes1 which contained an average of #bj4d pods each4 ,the racemes varied from #b to #aj cm4 in length1 and the number of pods to the raceme ranged from to #ge4 ,the racemes on the upper and most exposed portions of the plants were larger and the flowers produced a much higher percentage of pods than the racemes close to the bases of the larger branches4 ,many of the small racemes on the lower branches produced less than five pods each4 ,the data obtained from the two plants at ,arlington that were protected from night-flying insects may also be cited here1 as the results of that experiment show that night-flying insects are not an important factor in the production of sweet-clover seed1 and1 further4 because they were growing under the same conditions1 in the same plat1 and were approximately of the same size4 ,these two plants produced a total of #edd racemes1 with an average of #bj4i pods each4 ,the number of pods to the raceme varied from to #hf4 ,,efficiency ,,of ,,certain ,,kinds ,,of ,,insects ,,as ,,pollinators ,,of ,,sweet ,,clover4 ,in order further to test the self-sterility of sweet clover and to determine the relative efficiency of night-flying and of different kinds of day-flying insects as pollinators of the flowers1 a number of cages covered with cheesecloth1 glass1 or wire screen having #ad meshes to the linear inch were placed over plants at ,arlington4 ,va41 and at ,ames4 ,iowa1 in ,july and ,august4 #aiaf4 ,the bases of the cages were buried several inches in the ground1 so that insects could not pass under them4 ,cheesecloth was used to cover most of the cages and was made into sacks of such a size that they could be put on or removed from the frames of the cages without difficulty4 ,it was stretched tightly over the frames and fastened to their bases with laths4 ,a cage having two sides and the top of glass but with ends covered with cheesecloth to permit ventilation was used at ,ames to protect a number of plants from insect visitation at all times4 ,the purpose of this cage was to determine whether the partial shading of the plants in the cages covered with cheesecloth would have any effect upon the setting of seed4 ,the cage covered with wire netting having #ad meshes to the linear inch was used to determine the efficiency as pollinators of sweet clover of insects so small that they could pass through openings of this size4 ,the plants used in the experiments at ,arlington were growing close to the center of a field of sweet clover4 ,volunteer plants in a field that contained only a scattering stand were used at ,ames4 ,the cages were placed over the plants in all of these experiments before any of the flowers opened1 and the work was continued until they were through blooming4 ,,plants ,,subject ,,to ,,insect ,,visitation ,,at ,,all ,,times4 ,a plant subject to insect visits at all times and growing in the same plat as those inclosed in the cages at ,arlington was selected as a check to those inclosed in the cages during their entire flowering period or for only a portion of it4 ,this plant1 which was in bloom at the same time as those inclosed in the cages1 produced #aif racemes with an average of #bj4d pods each4 ,as all of the racemes were collected and as those on the lower portions of the plant were smaller than those on the upper branches1 the average number of seeds per raceme is much lower than it would have been if only the larger racemes had been collected4 ,an isolated plant that was subject to insect visits at all times was selected for a check to the cage work conducted at ,ames4 ,this was necessary in order to get results that would be comparable with those obtained from the plants inclosed in the cages1 as the cage experiments at ,ames were conducted with isolated plants4 ,the plant produced #bci racemes1 with an average of #da4f pods4 ,,plants ,,protected ,,from ,,insect ,,visitation ,,during ,,their ,,entire ,,flowering ,,period4 ,on ,july #c1 #aiaf1 a cage #c feet square and #c feet high1 covered with cheesecloth1 was placed over three sweet-clover plants at ,arlington4 7,fig4 #f47 ,this cage was not opened until ,august #c1 when practically all of the racemes had passed the flowering stage and the few seeds that formed on some of them were practically mature4 ,the three plants inclosed in the cage produced #ijd racemes1 with an average of #j4fc pod each4 ,no pods were produced on #eid racemes1 while #aej produced but one each4 ,none of the racemes produced more than five pods4 ,this experiment was duplicated at ,ames in ,august1 #aiaf1 with the result that the three protected plants produced a total of #ggf racemes1 with an average of #j4ai pod each4 ,illustration3 ,fig4 #f4--;,cage covered with cheesecloth to protect plants from insect visitation4 ,the plants inclosed at ,arlington produced #j4dd pod to the raceme more than the plants inclosed at ,ames1 and the average for the six plants at ,arlington and at ,ames is only #j4db pod to the raceme4 ,results given below for nine plants inclosed in the glass-covered cage show that the pods produced per raceme by different plants varied from #j4a to #j4de1 which is slightly less than the variation in the two cages covered with cheese-cloth4 ,in order to determine whether the shading of the plants in the cheesecloth-covered cages had caused the production of seed to be reduced1 a cage #d feet wide1 #d feet high1 and #aj feet long1 having glass sides and top1 but with ends covered with cheesecloth to permit ventilation1 was placed over nine plants at ,ames in ,august1 #aiaf4 ,the results obtained in this experiment are presented in ,table ,,iv4 ,table ,,iv4--,production of sweet-clover seed by plants protected from insect visitation during their entire flowering period at ,ames1 ,iowa1 in #aiaf4 ,racemes ,pods produced ,average number of ,plant4 per plant4 by all racemes4 pods to the raceme4 ---------------------------------------- ----------------- ,no4 #a #hd #ag #j4bj ,no4 #b #acj #eh 4#dd ,no4 #c #aff #cj 4#ah ,no4 #d #aii #hh 4#dd ,no4 #e #bdc #ce 4#bg ,no4 #f #aca #cf 4#bg ,no4 #g #aai #ac 4#aj ,no4 #h #ahb #hc 4#de ,no4 #i #cdj #adb 4#da ---------------------------------------- ------- ,total #a1eid #eib 4444444 ,average 4#ca ---------------------------------------- ----------------- ,the results given in ,table ,,iv show that an average of #j4ca of a pod to the raceme was obtained from #a1eid racemes and that the variation in seed production of the different plants was from #j4a to #j4de to the raceme4 ,the average seed production for the nine plants is #j4aa seed to the raceme less than the average results obtained from the six plants that were covered with cheesecloth4 ,as this difference is well within the limit of variation for individual plants1 it may be stated that the shading of the plants in the cheesecloth-covered cages did not reduce the production of seed4 ,the results of this experiment show that spontaneous self-pollination does not occur regularly1 as stated by ,kirchner4 ,,flowers ,,pollinated ,,only ,,by ,,night-,,flying ,,insects4 ,in order to determine the importance of night-flying insects as pollinators1 two cheesecloth-covered cages #c feet square and #c feet high were placed over sweet-clover plants at ,arlington on ,july #aj1 #aiaf4 ,the covers of the cages were removed each evening at #g3cj and replaced each morning at #d3cj o'clock4 ,practically all the flowers on these plants had bloomed by ,august #b1 and the seed produced was nearly mature4 ,the few racemes that contained opened flowers or buds were discarded4 ,the three plants in one cage produced #gbc racemes1 with an average of #c4gf pods each1 while the one plant in the other cage produced #bbg racemes1 with an average of #c4eh pods to the raceme4 ,the four plants1 therefore1 produced a total of #iej racemes1 with an average of #c4ga pods each4 ,the only night-flying insect found working on sweet clover while these plants were in bloom was ,diacrisia virginica ,fabr4 ,this experiment was duplicated at ,ames in ,august1 #aiaf1 with the result that one plant subject to visitation only by night-flying insects produced #dhf racemes1 with an average of #af4e pods each4 ,the results obtained in these experiments show that night-flying insects were much more active in pollinating sweet clover at ,ames than at ,arlington4 ,however1 as the results obtained from the plants subject to visitation by day-flying insects only were practically the same as those obtained from plants which were subject to insect visitation at all times1 it is concluded that night-flying insects were not a factor in the pollination of sweet clover at ,arlington or at ,ames in #aiaf4 ,,flowers ,,pollinated ,,only ,,by ,,day-,,flying ,,insects4 ,a cheesecloth-covered cage1 #c feet square and #c feet high1 was placed on ,july #g1 #aiaf1 over two sweet-clover plants at ,arlington1 before any of the flowers opened4 ,as the cover of this cage was removed at #g4cj a4 m4 and replaced at #d4cj p4 m4 each day during the experiment1 the plants were subject to visitation by day-flying insects only4 ,as soon as all of the flowers on most of the racemes had bloomed1 and before any mature pods shattered1 the racemes were removed from the plants and the pods produced by each raceme counted4 ,the two plants produced a total of #edd racemes1 with an average of #bj4i pods each4 ,this experiment was also conducted at ,ames4 ,one plant was protected from insect visitation at night in ,august1 #aiaf1 with the result that it produced #dah racemes1 with an average of #da4aa pods each4 ,,plants ,,protected ,,from ,,all ,,insects ,,that ,,could ,,not ,,pass ,,through ,a ,,wire ,,screen ,,having #ad ,,meshes ,,to ,,the ,,linear ,,inch4 ,it is well known that many small insects1 and especially those belonging to the family ,syrphid and to the genus ,halictus1 frequent sweet-clover flowers1 but no records have been noted that show how important these insects are as pollinators of this plant4 ,in order to obtain data on this subject a cage #ab feet square and #f feet high1 made of wire screen having #ad meshes to the linear inch1 was placed over a few plants at ,ames1 in ,july1 #aiaf1 before they began to bloom4 ,the base of the cage was buried several inches in the soil1 so that no insects could get into it4 ,as these plants were growing in a field where there was a sufficient supply of moisture at all times1 they made a growth of #e to #f feet4 ,for this reason all the racemes were collected from only a portion of one of the plants instead of from the entire plant1 as was done with the smaller ones inclosed in the cheesecloth-covered cages4 ,the branches selected contained #bbd racemes1 with an average of #bd4ec pods each4 ,many insects that were able to pass through the wire netting were observed working on the flowers of the inclosed plants4 ,a check plant1 subject to visitation by all insects and growing within a few yards of the cage1 contained #bfd racemes1 with an average of #bh4bc pods each4 ,this experiment shows that small insects are efficient pollinators of sweet clover and that the plant to which all insects had access produced an average of only #c4g pods to the raceme more than the one inclosed in the cage4 ,as these plants were growing close to a strip of timber and some distance from a field of sweet clover1 it is probable that more small insects worked on the flowers than would have been the case if the cage had been located in the center of a field of sweet clover4 ,though these results show that small insects are able to pollinate sweet-clover flowers freely1 it is very doubtful whether insects of this kind would be numerous enough to pollinate sufficient flowers in a large field of sweet clover for profitable seed production4 ,the honeybee is the most efficient pollinator of this plant1 and it is believed that in many sections it is responsible for the pollination of more than half of the flowers4 ,,summary ,,of ,,insect-,,pollination ,,studies4 ,the data secured in the different experiments where sweet-clover flowers were subject to insect visitation at one time or another are presented in detail in ,table ,v4 ,table ,v4--,summary of the insect pollination studies conducted at ,arlington1 ,va41 and ,ames1 ,iowa1 in #aiaf4 ---------------------------------------- ------------------------------ ,number of-- ,number -------------------------- ,location4 of ,method of treatment4 ,racemes4 ,pods ,pods per plants4 produced4 raceme1 average4 ---------------------------------------- ---------------------------- ,arlington4 #a ,check--subject to insect #aif #d1jac #bj4dg visitation at all times4 ,ames4 #a do4 #bci #i1idc #da4fj ,arlington4 #c ,protected from all #ijd #egg 4#fc insects4 ,ames4 #ab do4 #b1cgj #fec 4#bg ,arlington4 #c ,visited by night-flying #gbc #b1gbj #c4gf insects only 7cage #a74 ,do4 #a ,visited by night-flying #bbg #aeb 4#fg insects only 7cage #b74 ,ames4 #a ,visited by night-flying #dhf #h1jbd #af4ea insects only4 ,arlington4 #b ,visited by day-flying #edd #aa1cig #bj4ie insects only4 ,ames4 #a do4 #dah #ag1ahf #da4aa ,do4 #i ,protected from all #a1eid #ejb 4#ca insects4 ---------------------------------------- ---------------------------- ,the results in ,table ,v show that an average of #j4cg pod to the raceme was obtained from the plants protected from visitation by all insects during the flowering period4 ,as the racemes of ,melilotus alba will average approximately #ej flowers each1 less than #a per cent of them set seed without being pollinated by insects4 ,the results obtained in the cages in which only night-flying insects had access to the flowers show that these insects pollinate sweet clover to a slight extent1 but that the number of pods produced by them is so few that it may be assumed that these flowers would have been pollinated by day-flying insects4 ,this assumption is borne out by the results obtained in the cages where only day-flying insects had access to the flowers1 as the results obtained in these cages at ,arlington and ,ames1 respectively1 are approximately the same as those obtained on the plants subject to insect visitation at all times4 ,it will be noted that the yield of seed on the plants visited by insects at ,ames is much higher than that of the plants subjected to insect visits during the same period at ,arlington4 ,this difference in seed yield may be attributed to the fact that isolated plants were used in the experiments at ,ames1 and at ,arlington the experiments were conducted with plants growing under field conditions4 ,,relation ,,of ,,the ,,position ,,of ,,the ,,flowers ,,on ,,melilotus ,,alba ,,plants ,,to ,,seed ,,production4 ,observations of sweet-clover plants grown under cultivation1 and especially when the stands were thick1 showed that the flowers of the racemes on the upper and exposed branches produced a larger percentage of seed than those on the lower branches which were less exposed4 ,it is thought by some that the failure of the flowers on the lower racemes to be fertilized is due to shading2 but the results obtained in the cheesecloth and glass covered cages do not warrant this belief1 as it is doubtful whether the shading of the flowers on the lower racemes is more than that caused by the cheesecloth4 ,it is probably the lack of pollination that causes this decrease in seed production on the lower branches of plants growing close together1 as a vast number of flowers open each day on portions of the plants which are exposed directly to visitation by insects and are therefore more accessible to them4 ,in order to obtain information upon the number of flowers that produce seed on the upper and lower portions1 respectively1 of sweet-clover plants when grown under field conditions and where the stand contained four to five plants to the square foot1 a number of racemes were labeled on different portions of the plants at ,ames in #aiae and #aiaf4 ,when the pods were partly mature1 records were made of the number of flowers that produced pods4 ,the results obtained are given in ,table ,,vi4 ,table ,,vi4--,relation of the position of sweet-clover flowers on the plants to seed production1 at ,ames1 ,iowa1 in #aiae and #aiaf4 ---------------------------------------- ---------------------------- ,pods formed4 ,number of---------------------------- ,year4,position of the flowers4 flowers4 ,number4 ,percentage4 ,average4 ---------------------------------------- -------------------------- #aiae ,upper half of plants #hab #ceg #dc4i #aiaf do #bfa #aja #ch4g #db4f #aiae ,lower half of plants #cdd #dd #ab4g #aiaf do #baf #ei #bg4c #ah4c ---------------------------------------- -------------------------- ,the flowers on the upper racemes of the plants produced #ca4b per cent more pods than those on the lower racemes in #aiae4 and #aa4d per cent more in #aiaf4 ,these results prove that insects more frequently visit the flowers that are directly exposed and are therefore more accessible4 ,,influence ,,of ,,the ,,weather ,,at ,,blossoming ,,time ,,upon ,,seed ,,production4 ,the seed production of sweet clover is seldom satisfactory when rainy or muggy weather prevails during the flowering period4 ,in order to obtain data as to the relation existing between the visits of insects and the prevailing weather conditions1 a record of insect visits and of the number of flowers that opened each day was kept for a period of nine days at ,ames in ,august1 #aiae4 ,in this experiment the racemes were marked early each morning just above the last flowers which had opened the previous day1 and early the following morning the number of flowers which had opened the previous day was noted4 ,the number of flowers that were pollinated was determined by the number of pods that formed4 ,table ,,vii gives in detail the results obtained4 ,table ,,vii4--,influence of the weather at blossoming time upon the yield of sweet -clover seed1 at ,ames4 ,iowa1 in #aiae4 ---------------------------------------- -------------------------- ,number of ,percentage ,date1 ,weather conditions4 ,insect flowers ,pods of flowers #aiae4 visitors4 that formed4 that opened4 matured4 ---------------------------------------- -------------------------- ,aug4 #af;,cloudy and showery ,very few #ajb #ah #ag4f ,aug4 #ag,rain all day ,none #fi #d #e4g ,aug4 #ah;,cloudy most of the day ,very few #fj #bj #cc4c ,aug4 #ai;,clear and cool ,numerous #id #ec #ef4c ,aug4 #bj,mostly clear and warm do #fa #ch #fb4b ,aug4 #ba;,clear and warm do #ha #dd #ed4c ,aug4 #bb,partly cloudy and warm ,aug4 #bc do do #aha #ajj #ee4b ,aug4 #bd;,cloudy till mid-afternoon ,few #cg #ab #cb4d ---------------------------------------- -------------------------- ,the data given in ,table ,,vii show that the percentage of effective pollination is much higher in clear weather1 when insects are active1 than in cloudy or rainy weather1 when but few insects visit the flowers4 ,,insect ,,pollinators ,,of ,,sweet ,,clover4 ,on account of the ease with which the heavy flow of nectar of sweet-clover flowers may be obtained many insects visit the flowers1 thereby pollinating them4 ,while the useful insect visitors of flowers of red clover are limited to a few species of ,hymenoptera1 those pollinating sweet-clover blossoms are many and belong to such orders as ,coleoptera1 ,lepidoptera1 and ,diptera1 as well as to the ,hymenoptera4 ,however1 in the ,united ,states the honeybee is the most important pollinator of sweet clover4 ,in many parts of the country the different species of ,halictus1 commonly known as sweat bees1 rank next in importance4 ,the margined soldier beetles 7,chauliognathus marginatus ,fabr47 were very active pollinators at ,arlington1 ,va41 in the latter part of ,june and first part of ,july1 #aiaf1 but the woolly bear 7,diacrisia virginica ,fabr47 was the only night-flying insect found working on sweet clover at ,arlington4 ,insects belonging to the genera ,halictus1 ,syritta1 and ,paragus were very active pollinators at ,ames1 ,iowa1 in #aiaf1 and ranked next in importance to the honeybee4 ,in fact1 the results obtained in the cage where the plants were protected from visitation by insects that could not pass through a screen having #ad meshes to the linear inch showed that these small insects were able under the conditions of that experiment to pollinate practically as many flowers as larger insects4 ,the insects listed below were collected while visiting ,melilotus alba and ,m4 officinalis flowers in #aiaf4 ,,at ,,arlington1 ,,va4 ,neuroptera4--,perithemis domitia ,dru41 ,enallagma sp4 ,hemiptera4--,adelphocoris rapidus ,say1 ,lygus pratensis ,linn1 7tarnished plant bug74 ,coleoptera4--,chauliognathus marginatus ,fabr4 7margined soldier beetle71 ,diabrotica #ab-punctata ,oliv4 7southern corn rootworm74 ,lepidoptera4--,pieris protodice ,bd4 7imported cabbage butterfly71 ,heodes hypophleas ,bd41 ,lycaena comyntas ,gdt41 ,hylephila campestris ,bd41 ,scepsis fulvicollis ,hubn41 ,ancyloxypha numitor ,fabr41 ,pholisora catullus ,fabr41 ,pyraustid sp41 ,loxostege similalis ,gn4 7garden webworm71 ,thecla melinus ,hubn41 ,colias philodice ,gdt4 7the common sulphur butterfly71 ,tarachidia caudefactor ,hubn41 ,pyrameis atalanta ,linn41 ,drasteria 7#b species71 ,diacrisia virginica ,fabr4 7the woolly bear74 ,hymenoptera4--,halictus lerouxi ,lep41 ,h4 provancheri 7sweat bee71 ,h4 pectoralis ,sm4 7sweat bee71 ,halictus 7#c unidentified species71 ,h4 legatus ,say1 ,bombus affinis ,cr41 ,b4 impatiens ,harris 7bumblebee71 ,melissodes bimaculata ,lep41 ,polistes pallipes ,lep4 7paper wasp71 ,megachile sp4 7leaf-cutter bee71 ,coelioxys octodentata ,say1 ,xylocopa virginica ,drury 7common carpenter bee71 ,pompiloides sp41 ,apis mellifica ,linn1 7honeybee71 ,philanthus punctatus ,say1 ,sphex nigricans ,dahlb4 7caterpillar hawk71 ,s4 pictipennis ,walsh 7caterpillar hawk74 ,diptera4--,archytas analis ,fabr41 ,chrysomyia macellaria ,fabr4 7screw-worm fly714 ,pollenia rudis ,fabr4 7cluster fly71 ,ocyptera carolinae ,desv41 ,trichophora ruficauda ,v4 ,d4 ,w41 ,eristalis arbustorum ,linn41 ,physocephala tibialis ,say4 ,,at ,,ames1 ,,iowa4 ,hemiptera4--,lygus pratensis ,linn41 ,adelphocoris rapidus ,say1 ,coleoptera4--,coccinella transversoguttata ,fabr4 ,lepidoptera4--,eurymus eurytheme ,bdv41 ,chrysophanus sp41 ,lycaena 7#b species714 ,libythea bachmani ,kirtland1 ,pieris rapae ,linn4 ,hymenoptera4--,angochlora sp41 ,apis mellifica ,linn41 ,colletes sp41 ,halictus lerouxi ,lep41 ,h4 provancheri ,d4 ,j41 ,halictus sp41 ,elis sp41 ,calliopsis andreniformis ,smith1 ,polistes sp41 ,sphex sp41 ,eumenes fraterna ,say1 ,sceliphron sp41 ,isodontia harrisi1 ,fern41 ,cerceris sp41 ,oxybelus sp4 ,diptera4--,syritta sp41 ,paragus sp41 ,chrysomyia macellaria ,desv41 ,syrphid 7#b unidentified specimens74 ,,effect ,,of ,,moisture ,,upon ,,the ,,production ,,of ,,melilotus ,,alba ,,seed4 ,careful inspection of a number of sweet-clover fields in ,iowa and ,illinois in the autumn of #aiaf indicated that many plants were unable to obtain sufficient moisture for the proper development of their flowers4 ,examination of flowers that aborted shortly after reaching their mature size showed that the anther sacs had not burst1 even though the pollen grains were mature4 ,apparently for the same reason many immature pods aborted4 ,the precipitation for ,july1 #aiaf1 in ,livingston ,county1 ,ill41 where the sweet-clover seed crop suffered materially for lack of moisture1 was #c4b inches less than normal1 while the temperature was #d4e ,f4 above normal4 ,in ,august the precipitation was #j4if of an inch below normal and the temperature #d4b ,f4 above normal4 ,at ,ames1 ,iowa1 the precipitation was #c4ed inches below normal and the temperature #e4d ,f4 above normal in ,july4 ,both the precipitation and temperature were about normal at ,ames in ,august1 but most of the precipitation fell before the experiments were commenced4 ,in north-central ,illinois the seed production of sweet clover was very irregular4 ,some fields produced an abundance of seed1 while a large percentage of the pods on the plants in other fields near by1 where the thickness of the stand1 size of the plants1 and conditions in general were approximately the same1 aborted4 ,it was evident that all stands producing a good seed crop were growing on well-drained soil and that those which were not yielding satisfactorily were on poorly drained land4 ,it is well known that sweet clover will produce deep taproots only when the plants are growing in well-drained soil and that a much-branched surface root system will be formed on poorly drained land1 and especially when there is an excess of moisture or a high water table during the first season's growth4 ,during this droughty period in #aiaf the upper layer of soil became so depleted of moisture that the plants with surface root systems were unable to obtain sufficient water to mature their seed4 ,on the other hand1 the lack of precipitation and the high temperatures did not affect the moisture content of the subsoil sufficiently to interfere with the normal seed production of deep-rooted plants4 ,according to ,lutts 7#bb1 p4 #dg7 this same condition was found to be true in ,ohio in #aiaf4 ,as a rule1 under droughty conditions the second crop of sweet clover will produce a higher yield of seed than the first crop1 as the second growth of the plants is seldom more than half as much as the first1 thereby requiring less moisture4 ,however1 if showery hot weather prevails when the first crop is cut1 the end of each stub is very apt to become infected1 usually with a species of ,fusarium1 which kills all the cortex as far back as the upper bud or young shoot and that part of it on the opposite side of this bud to the bud below4 ,if the second bud from the top of a stub is not directly opposite the upper one the decay may extend nearly to the ground4 7,pl4 ,,iv47 ,the destruction of half to two-thirds of the cortex from #b to #d inches below the upper bud materially reduces the quantity of water that can be conveyed to the branch above the base of the dead area4 ,plants thus infected obtain sufficient moisture for seed production only under the most favorable conditions4 ,when the first crop is cut during warm dry weather1 and especially when the first crop has not been permitted to make more than a #cj to #cb inch growth1 the stubble seldom decays1 and in no instance have the plants been observed to decay as far back as the upper buds4 ,an experiment was conducted at ,ames in the latter part of ,august and first part of ,september1 #aiaf1 to determine the effect of watering plants that were aborting a large percentage of their flowers and immature pods4 ,for this purpose several volunteer plants growing in a meadow were selected4 ,a hole #ab inches square and #ad inches deep was dug #h inches from the crown of one plant1 and each evening during the experiment #b gallons of water were poured into the hole4 ,the top of the hole was kept covered1 so as to check evaporation from it as much as possible4 ,another plant of the same size and growing about #ae yards from the watered plant served as a check4 ,on both plants many of the flowers and immature buds were aborting at the beginning of the experiment4 ,the soil in this field was so depleted of moisture that the leaves of the plants wilted during the hottest part of the days preceding the experiment4 ,the foliage on the check plant wilted each day for the first five days of the experiment4 ,on the sixth day #j4if of an inch of rain fell and four days later #j4bc of an inch more4 ,the dropping of the flowers was temporarily checked by these precipitations1 but owing to the dry1 compact condition of the soil the rain was not sufficient to check entirely the fall of flowers and immature pods4 ,at the beginning of the experiment the racemes on both plants were divided into three classes1 according to the development of the flowers1 and labeled4 ,they were collected and the seeds counted as soon as the pods at the bases of the racemes commenced to turn brown4 ,table ,,viii presents the results obtained4 ,table ,,viii4--,effect of water upon the seed production of sweet clover when growing under droughty conditions at ,ames1 ,iowa1 in #aiaf4 ---------------------------------------- ------------------------------ ,plant not watered4 ,plant watered4 ---------------------------------- ,average ,average ,stage of development ,number number of ,number number of,increase when labeled4 of pods per of pods per from racemes raceme racemes raceme watering4 labeled4 that labeled4 that matured4 matured4 ---------------------------------------- --------------------------- ,flowers at the base of the racemes just ready #di #bg4ci #aaj #ee4fc #bh4bd to open4 ,pods #c to #f days old #cj #ba4ac #aab #ci4ha #ah4fh ,pods #i to #ab days old #ce #ae4bc #ej #bi4hf #ad4fc ---------------------------------------- --------------------------- ,the effect of the water was noticeable soon after the first application1 as the leaves and flowers on this plant became turgid and the anther sacs burst at the proper stage of their development4 ,very few flowers fell after the second day4 ,the water decidedly checked the aborting of immature pods1 as is shown by the results obtained on the racemes which were labeled after the pods had formed4 ,the racemes which contained pods #c to #f days old when labeled matured #i4ie pods to the raceme more than those which contained older pods at the beginning of the experiment1 but this was expected1 as most of the aborting which caused this difference had taken place before the racemes were labeled4 ,as very few pods aborted before they were #c to #f days old1 the difference of #i4ie pods to the raceme in favor of the ones labeled when the flowers at their bases were just ready to open was largely due to the dropping of the flowers on the older racemes before the experiment was begun4 ,it will be seen that the production of mature pods on the plant not watered was much greater on the racemes that were labeled before the flowers opened than on the older racemes4 ,this difference is undoubtedly due to the precipitation which fell on the sixth and tenth days of the experiment4 ,it is believed that the yield of #ae4bc pods to the raceme on the ones labeled when the pods were #i to #ab days old is representative of the production of pods per raceme previous to the precipitation and that the other racemes on this plant would have yielded proportionately if conditions had remained the same4 ,in the early spring of #aiaf1 ,melilotus alba was planted in several large pots in the greenhouse of the ,department of ,agriculture at ,washington1 ,d4 ,c4 ,these pots were placed outside the greenhouse in the late spring1 where they remained until the following ,january1 when they were taken into the greenhouse4 ,the plants grew rapidly and began to flower during the latter part of ,april1 #aiag4 ,at this time two pots were placed in a large cage made of screen having #bj meshes to the linear inch4 ,one pot was submerged in a tub of water1 so that the soil was saturated at all times1 while the plant in the other pot was given only sufficient water to keep it from wilting4 ,the pods on a few racemes were self-pollinated and the results obtained are given in ,table ,,ix4 ,table ,,ix4--,effect of moisture on the seed production of ,melilotus alba at ,washington1 ,d4 ,c1 in #aiag4 ---------------------------------------- ---------------------------- ,total number of-- ,flowers that matured 7per cent74 ---------------------------------------- -- ,soil treatment4 ,pods ,racemes4 ,flowers4 formed4 ,total4 ,increase4 ---------------------------------------- --------------------------- ,soil given only a limited #ab #bbg #fe #bh4fc 444444 quantity of water4 ,soil saturated4 #ag #dbe #bce #ee4jc #bf4bb ---------------------------------------- --------------------------- ,the results of this experiment compare favorably with those obtained under field conditions at ,ames in #aiaf4 ,part ,,ii4--,,structure ,,and ,,chemical ,,nature ,,of ,,the ,,seed ,,coat ,,and ,,its ,,relation ,,to ,,impermeable ,,seeds ,,of ,,sweet ,,clover4#c #c ,the writers wish to acknowledge the service rendered by ,mr4 ,h4 ,s4 ,doty1 ,instructor in ,botany1 ,iowa ,state ,college1 ,ames1 ,iowa1 in assisting in the preparation of this article4 ,,historical ,,summary4 ,when agriculturists first began to cultivate wild legumes they observed that many seeds would not germinate within a comparatively short time after planting4 ,thus the problem of impermeable seeds began to demand attention many years ago4 ,however1 impermeable seeds are not confined to the ,leguminos1 as they occur also in the ,malvace1 ,chenopodiace1 ,convolvulace1 ,cannace1 and other families4 ,since the first account of the structure of legume seed coats by ,malpighi 7#bc v4 #a7 in #afhg1 many investigators have contributed to our knowledge of the structure of the coats of seeds belonging to this family4 ,pammel 7#ca7 made an extensive study of legume seeds1 including all the genera in the sixth edition of ,gray's ,manual1 as well as genera not included in that publication4 ,he found that the seed coat uniformly consisted of three layers1 namely1 the outer layer of ,malpighian cells1 the osteosclerid layer1 and the inner layer of nutrient cells4 ,pammel's work included a study of the seed coats of ,melilotus alba and ,m4 officinalis1 and the descriptions and illustrations in his publication agree for the most part with the results obtained in the investigations reported in this article4 ,however1 more variation was noticed in the different layers of the seed coat than he describes4 ,the cause of impermeability in seeds has been investigated by many4 ,it has been found to be due to the embryos in some seeds1 such as the hawthorns1 but in most cases to the structure of the seed coat1 and especially so in the ,leguminos4 ,crocker 7#c7 states that1 exactly opposite to the common view1 the cause of delayed germination generally lies in the seed coats rather than in the embryos4 ,nobbe 7#bi7 thought that the hardness of leguminous seeds was due to the ,malpighian layer1 and in a later publication ,nobbe and ,haenlein 7#cj1 p4 #ha7 state that the absorbent power of many seeds is inhibited or entirely arrested by the cones of the ,malpighian cells and the shields built up between them1 which consist principally of cutin4 ,huss 7#ae7 agrees with ,nobbe and ,haenlein4 ,verschaffelt 7#ci7 found that the impermeability of the seeds of ,csalpiniace and ,mimosace investigated was due to1 the inability of water to pass through the canals of the seed coat4 ,by soaking the seeds in alcohol or other substances which change the capillarity of the pores1 the seed coats were made readily permeable to water4 ,gola 7#f7 states that the cause of the impermeability of seeds is the peculiar character of the ,malpighian cells1 which prevents their infiltration and consequent increase in volume1 while ,bergtheil and ,day 7#b7 found that the hardness of the seeds of ,indigofera arrecta was due to their possession of a very thin outer covering of a substance resistant to water4 ,ewart 7#e1 p4 #ahe7 believes that in most impermeable seeds the cuticle prohibits the absorption of water1 but gives as an exception ,adansonia digitata1 in which the whole integument seems to be permeable to water with difficulty4 ,the following is quoted from ,white 7#db1 p4 #bje73 ,as a general rule in small and medium-sized seeds the cuticle is well developed and represents the impermeable part of the seed coat1 while in the cases of large seeds1 such as those of ,adansonia gregorii1 ,mucuna gigantea1 ,wistaria maideniana1 and ,guilandina bonducella1 the cuticle is relatively unimportant and inconspicuous4 ,in these seeds the extreme resistance which they exhibit appears to be located in the palisade cells4 ,in discussing the seed coat of ,melilotus alba1 ,rees 7#cc1 p4 #djd7 states that the outer layer consists of palisade cells covered1 externally by a structureless membrane1 which1 however1 did not appear to be cuticle but hemicellulose1 as it stained magenta with chloriodid of zinc4 ,the greater part of the walls of the palisade cells also appears to be composed of hemicellulose and the outer ends only were cuticularized4 ,in order to find whether the outer membrane was in itself impermeable to water1 this author treated seeds for short intervals in sulphuric acid to dissolve the outside covering without directly affecting the palisade cells4 ,seeds treated in this manner swelled in water and microscopic examination showed that the ends of the palisade cells were quite intact1 but had separated from each other4 ,from this it was concluded that the outer membrane is instrumental in conferring impermeability on the seed1 although not directly responsible for it1 as is the case with a true cuticle4 ,it is further believed that it probably served as a cement substance by means of which the cuticularized ends of the cells were held together closely1 thus forming a barrier through which water could not penetrate1 but that as soon as this barrier was removed the ends of the palisade cells separated and water passed in between them4 ,more than #bj years ago machines were devised by ,kuntze1 ,michalowski 7#bg1 p4 #hf71 ,huss 7#ae71 and later by ,hughes 7#ad71 to scarify impermeable seeds4 ,other methods have been recommended and employed to some extent for hastening the germination of seeds4 ,hiltner 7#ac1 p4 #dd7 treated seeds of red clover1 white clover1 and alfalfa #aj1 #cj1 and #fj minutes with concentrated sulphuric acid and found that the best germination resulted from the #fj-minute treatment4 ,love and ,leighty 7#ba7 also treated the seeds of various legumes with concentrated sulphuric acid and obtained a better germination in all cases4 ,in their investigations with ,melilotus alba it was found that a #b-;hour treatment resulted in some injury to the seed1 but that a treatment varying from #be minutes to #a hour gave good results4 ,in most cases in our investigations the seed coats of sweet clover became permeable to water after a treatment of #ae minutes in concentrated sulphuric acid1 and within #e minutes all of the ,malpighian cells were destroyed down to the light line4 ,harrington 7#aj7 found that the soil1 season1 climate1 color1 or size of red-clover seeds had no influence upon the percentage of impermeable seeds and that the good germination ordinarily obtained with red clover was due to the scarifying of the seed coats by the rasps of hulling machines4 ,harrington 7#aa7 also studied the agricultural value of impermeable seeds and found that alternations of temperature cause the softening and germinating of many impermeable clover seeds when a temperature of #aj ,c4 or cooler is used in alternation with a temperature of #bj ,c4 or warmer and that the effect of such an alternation of temperature is greatly increased by previously exposing the seeds to germinating conditions at a temperature of #aj ,c4 or cooler and is decreased by previously exposing the seeds to germinating conditions at a temperature of #cj ,c4 ,it is a well-known fact that impermeable seeds which remain in the field over winter germinate readily the following spring4 ,the light line is the most important and interesting feature of the ,malpighian cell1 at least so far as ,melilotus alba and ,m4 officinalis are concerned4 ,but one light line occurs in the ,malpighian cells in most ,leguminos1 although ,pammel 7#cb7 reports two well-developed light lines in ,gymnocladus canadensis1 ,junowicz 7#af7 found three in ,lupinus varius1 and ,sempolowski 7#cf7 two in ,lupinus angustifolius4 ,many investigators have studied the light line1 and different theories have been advanced as to its function1 physical properties1 and chemical nature4 ,schleiden and ,vogel 7#ce1 p4 #bf7 in describing the mature testa of ,schizolobium excelsum in #ahch undoubtedly referred to the light line when they stated that the walls of the ,malpighian cells were not equally thickened4 ,mettenius 7#bf71 in #ahdf1 was probably the first definitely to describe the light line4 ,this author believed it was composed of pore canals1 all appearing at the same height in the cells1 but he was unable to prove this by cross sections4 ,lohde 7#bj7 studied the light line in seeds of ,hibiscus trionum and found it cutinized4 ,hanstein 7#h7 states that the ,malpighian cells are composed of two cell layers and the light line is produced by the adjoining walls of the ends of the cells4 ,later1 this same author 7#i71 according to ,harz 7#ab71 refers to the light line as a perforated disk composed of tissue of strong refracting power4 ,russow 7#cd7 concludes that the light line is produced by neither chemical nor mechanical changes but is caused by a modified molecular structure containing less water than the remainder of the cell wall4 ,hiltner 7#ac7 agrees with ,russow's explanation4 ,harz 7#ab1 p4 #efa7 also agrees with ,russow and adds that he has observed that the light line disappeared in a number of cases after applications of nitric acid4 ,wigand and ,dennert 7#dc7 suggested that the light line is due to a series of erect fissures1 while ,tietz 7#cg1 p4 #cb7 believes it is due to a chemical modification and that the phenomenon results from the exceptionally extreme density of parts of the cellulose membrane4 ,junowicz 7#af7 found evidence of cellulose material4 ,the cell wall at this point was strongly refractive and had a different molecular structure4 ,after studying ,phaseolus vulgaris1 ,haberlandt 7#g1 p4 #ch7 agrees with the ,russow explanation4 ,in the seed of this plant the light line colored blue after being treated with chloriodid of zinc4 ,sempolowski 7#cf71 who investigated the light line in ,lupinus angustifolius1 states that there is not only a difference in the molecular structure but also a chemical modification of the cell wall at this point1 since with iodin and sulphuric acid the cell wall colored blue1 whereas the light line colored yellow4 ,wettstein 7#da71 who studied seeds of ,nelumbo1 agrees with ,russow 7#cd7 and ,sempolowski 7#cf7 that chemical and physical modifications occur4 ,he found that iodin and sulphuric acid colored the ,malpighian cells intensely blue1 the light line at first yellowish1 and then later it gradually became blue4 ,this reaction may be accelerated by heat4 ,iodin produced the same effect1 and the light line colored blue more rapidly4 ,when treated with a water-withdrawing medium the light line was not altered for some time1 but finally disappeared with continued application4 ,cooking for a long time in caustic potash or standing in cold caustic potash caused the cells to swell1 while the light line remained uninjured at first but finally disappeared4 ,he also believed that the absence of pore canals in the region of the light line caused it to be more dense4 ,nobbe and ,haenlein 7#cj7 treated sections of seed coats of ,trifolium pratense with iodin and sulphuric acid and found that the light line colored blue as readily as the thickened ridges that radiate inward from it1 but that the outer processes of the palisade cells projecting from the light line toward the cuticle stained dark brown4 ,they also state that various causes work to produce such unusual lusters in the light line1 the principle one of which is the thickened ridges which radiate inward1 reach their greatest development at this point1 and coalesce in the lumen of the cell4 ,the result is that the light line falls upon a continuously homogeneous medium1 while in the inner portions of the ridges the light passes through media of varying opacity1 such as cellulose1 water1 and protoplasm1 whereby it is progressively subdued in varying degrees by partial reflection4 ,pammel 7#ca1 p4 #adg7 studied the light line in ,melilotus alba and found that it consisted of a narrow but distinct refractive zone below the conical layer4 ,the refractive zone colored blue with chloriodid of zinc4 ,the whole upper part was1 however1 more or less refractive1 while the remainder of the cell wall contained pigment and colored blue with chloriodid of zinc4 ,small canals project into the walls1 in some cases extending beyond the light line4 ,beck 7#a7 found that the light-refracting power of the light line was much greater than that of the undifferentiated membrane and stated that there may be in addition to this a chemical difference which can not be detected with the present microchemical methods4 ,he does not believe that it is cuticularized or that it contains less water than the rest of the cell4 ,marlire 7#bd1 p4 #aa7 gives a physical explanation and states that the true cause of the light line lies in the peculiar structure of the secondary membrane of the ,malpighian cell4 ,tunmann 7#ch1 p4 #eei7 observed that it did not hydrolize in weak acids and therefore decided that it was not hemicellulose4 ,he found that it dissolved in concentrated sulphuric acid more readily than the regions surrounding it and that it was composed of pectin or callose4 ,in our investigations the main portion of the light line of ,melilotus alba and ,m4 officinalis was very resistant to concentrated sulphuric acid1 only the narrow outer portion being attacked4 ,it showed evidence of callose4 ,,material ,,and ,,methods4 ,permeable and impermeable seeds#d of ,melilotus alba and ,m4 officinalis were obtained from commercial samples and also from samples collected in the field4 ,those selected for sectioning were allowed to dry after being removed from the germinator and then embedded on the ends of pine blocks in glycerin gum1 which was made by dissolving #aj grams of powdered gum arabic in #aj c4 c4 of water and adding #dj drops of glycerin4 ,after the glycerin gum had dried for #bd hours1 the seeds were easily sectioned4 ,this method of embedding causes no change in the seed coat4 ,it is more satisfactory than the paraffin method for holding the seeds firmly4 ,the glycerin gum dissolved readily when the sections were mounted in water4 #d ,the term permeable is used in this paper to designate seeds whose coats are permeable to water in two weeks or less at temperatures favorable for germination1 while the term impermeable is used to designate seeds whose seed coats are impermeable to water for this length of time when temperatures are favorable for germination4 ,impermeable seeds are commonly referred to as hard seeds1 and they may become permeable in time4 ,in the microchemical studies ,sudan ,,iii1 alcanin1 chlorophyll solution1 and phosphoric acid iodin were used to test for cutin or suberin2 sulphuric acid and iodin1 chloriodid of zinc1 and chloriodid of calcium for cellulose2 phloroglucin and hydrochloric acid for lignin2 ruthenium red for pectic substances2 and sulphuric acid1 ,congo red1 and aniline blue for callose4 ,where very thin sections were necessary for detailed study of the structure of the seed coat1 pods in various stages of development were collected1 and after the usual preliminary treatment they were embedded in paraffin and sectioned with the microtome4 ,microchemical tests were made with these sections by using various specific stains4 ,safranin was used to test for cutin1 suberin1 and lignin2 haematoxylin and methyl blue for cellulose 2 methylene blue1 methyl violet ,b1 mauvein1 and ruthenium red for pectic substances2 and aniline blue and ,congo red for callose4 ,in studying some points with reference to the pore system of the seed coat1 it was necessary to use free-hand sections of fresh pods4 ,in studying the seed coat in relation to the absorption of water1 both permeable and impermeable seeds were soaked in water solutions of safranin1 gentian violet1 eosin1 and haematoxylin1 then dried and embedded in glycerin gum for sectioning4 ,seeds were soaked in stains dissolved in #ie per cent alcohol to test the penetration of alcohol4 ,it was evident that the seed coats did not act as a filter1 as the stains passed through them with the water or alcohol4 ,,structure ,,of ,,the ,,seed ,,coat4 ,there is very little endosperm present in mature seeds of ,melilotus alba or ,m4 officinalis4 ,that which is present is quite permeable to water and therefore bears no relation to the impermeable seeds of these plants4 ,the outer layer of the seed coat1 which is the modified epidermal layer of the ovule1 is known as the ,malpighian layer4 7,pl4 ,v1 figs4 #a and #b47 ,the cells constituting this layer1 commonly called palisade cells1 are the most highly modified cells of the seed coat4 ,they are very much elongated1 their length varying in the different regions of the coat1 and their outer tangential walls and the outer portions of their radial walls are so much thickened that their lumina are confined to the inner portion of the cells1 sometimes occupying less than half the length of the cells4 ,the inner tangential walls and inner portions of the radial walls are thickened just previous to the death of the cells1 the thickening sometimes being only slight and sometimes so much as to leave only very narrow lumina4 ,there is a very thin layer on the outer surface of the ,malpighian cells which has been called cuticle by previous investigators1 but the chemical composition of this layer and its perviousness to water indicate that there is very little cutin present4 ,this layer is probably the primary epidermal cell wall rather than a deposit on the outer surface of the wall4 ,to determine this a study of the development of the ,malpighian cells is necessary4 ,beneath the so-called cuticle there is the much thickened outer portion of the ,malpighian cells in which there are two rather distinct regions1 one constituting the conelike structures and the other forming a continuous layer over the conelike structures1 separating them from the cuticle and filling in between them4 ,these two regions separate easily1 and in cutting sections the outer region1 called by some the cuticularized portion1 often breaks away1 leaving the entire surface of the cones exposed4 ,the term cuticularized layer will be used to designate all of the thickening covering the cones1 including that around the cones as well as the portion between the cones and the cuticle4 ,this term is not entirely appropriate1 for the region is practically free from cutin1 but for the want of a better term it will be used4 ,there are canals in the cuticularized layer and cones1 which are easily seen when the sections are treated with chloriodid of zinc or sulphuric acid4 ,a surface view of a section showing the cones and cuticularized layer when mounted in glycerin shows the canals as dark lines due to the air inclosed4 ,the canals are most abundant along the lines where the lateral walls of the cells join1 but many are within the cones and in the cuticularized substance between the cones4 7,pl4 ,v1 fig4 #e47 ,the well-developed light line in ,melilotus alba and ,m4 officinalis is found just below the bases of the cones4 ,in some seed coats only a few and in others none of the canals which are common in the cones and cuticularized region cross the light line4 ,a very distinct line of small canals filled with air and thus forming a dark band is present just above the fight line1 thus making the light line more conspicuous4 7,pl4 ,v1 fig4 #c47 ,when the lumina of the cells extend across the light line1 they are exceedingly small4 ,the light line is the most compact region of the ,malpighian layer and is conspicuous because it refracts the light much more than the regions above and below it4 ,just below the ,malpighian is a layer of cells variously modified and known as the osteosclerid4 ,the cells of this layer are often referred to as the hourglass cells on account of their shape4 ,in some regions of the seed coat they are expanded at both ends and their walls are much thickened1 the thickenings forming ridges on the radial walls1 while in other regions only the upper tangential wall and a portion of the radial walls are thickened and the cells are expanded only at the inner end1 thus having the shape of the frustum of a cone4 ,beneath the osteosclerid layer is the nutrient layer4 ,the nutrient layer contains chloroplasts4 ,it varies not only in the number of layers of cells composing it1 but also in the modifications of these cells4 ,this layer ranges from four to seven cells in thickness in the different parts of the seed coat4 ,,plate ,v4 ,illustration ,structure of the ,seed ,coat of ,sweet ,clover4 ,fig4 #a4--,section of the seed coat of ,melilotus officinalis4 #dej4 ,fig4 #b4--;,another section of the seed coat of ,melilotus officinalis1 showing the variation in size and modifications that occur in the three layers4 #dej4 ,fig4 #c4--,section of the ,malpighian layer of a ,melilotus alba seed1 showing a line of canals just above the light zone4 #dej4 ,fig4 #d4--,section of the ,malpighian layer of a permeable ,melilotus alba seed4 #dej4 ,fig4 #e4--,tangential section of the ,malpighian cells cut between the cuticle and tops of the cones1 showing pores4 #ecj4 ,fig4 #f4--,section through the ,malpighian layer of an impermeable ,melilotus alba seed4 #dej4 ,fig4 #g4--,section through the ,malpighian layer of an impermeable ,melilotus alba seed1 showing the region through which water and stains readily passed4 #dej4 ,fig4 #h4--;,cross section of a ,malpighian cell of a permeable ,melilotus alba seed through the region of the light zone1 showing the lumen not entirely closed4 #ecj4 ,fig4 #i4--,section through the ,malpighian layer of a ,melilotus alba seed shaded to show the portions which react to the cellulose and pectose tests4 #dej4 ,fig4 #aj4--,section through the ,malpighian layer of a ,melilotus alba seed which shows the condition of the seed coat after #fj minutes' treatment of concentrated sulphuric acid4 ,that portion above the light zone was destroyed1 and the lumina as small pores through which much of the stain now passed were seen extending across the light line4 ,the lines between the cells were much more distinct1 appearing as small intercellular spaces through which some stain passed4 #dej4 a1 ,cuticle2 b1 cuticularized layer2 c1 conelike portion of the thickening of the ,malpighian cells2 d1 light line2 e1 region of a hard seed coat through which water and stains readily passed2 l1 lumen2 ,m1 ,malpighian cells2 ,n1 nutrient cells2 ,o1 osteosclerid cells2 p1 canals just above light zone4 ,,microchemistry ,,of ,,the ,,seed ,,coat4 ,tests for cutin showed that there was very little present in the seed coat4 ,slight reactions for cutin were observed in the cuticle1 in the outer margin of the cuticularized layer1 and in the basal portion of the cones4 ,these reactions were so slight as to be almost negligible4 ,it is evident that the cuticle and cuticularized layer are not well named in ,melilotus alba and ,m4 officinalis4 ,tests for cellulose showed that it was present in the cuticle1 cuticularized layer1 cones1 the walls of the ,malpighian cells below the light line1 and the walls of the cells of the osteosclerid and nutrient layers4 7,pl4 ,v1 fig4 #i47 ,the reaction for cellulose in the ,malpighian cells was quite distinct in the walls below the light line1 less distinct in the cones and cuticle1 and least distinct in the cuticularized layer4 ,tests for lignin occasionally showed slight traces in the ,malpighian cells below the light line4 ,when treated with reagents for pectic substances1 the cuticle1 cuticularized layer1 cones1 and all cell walls below the light line gave a definite reaction4 ,the reaction of the cones and cuticle was more pronounced than the cuticularized layer4 ,tests for callose gave no reaction except in the upper part of the light line4 ,this part of the light line stained slightly blue with aniline blue and was easily dissolved with sulphuric acid4 ,in cutting free-hand sections of fresh material the ,malpighian layer sometimes broke along this line4 ,the greater part of the light line reacted to none of the tests1 and its chemical nature was not determined4 ,when microtome sections of seeds in different stages of development were treated with various stains1 the results were in accord with those obtained with free-hand sections4 ,thus with safranin the periphery and cones of the ,malpighian cells were slightly stained1 while haematoxylin and methyl blue stained all the seed coat except the light line4 ,the cones and cuticle stained more readily than the cuticularized layer1 but neither stained as deeply as the cell walls below the light line4 ,methylene blue1 methyl violet ,b1 and mauvein stained all above the light line1 indicating the presence of pectic substances2 however1 the staining was more prominent in the cones and cuticle4 ,the difference in reaction of the cones and cuticularized layer to the cellulose and pectose tests probably indicates a difference in density rather than a difference in chemical composition4 ,since the cuticularized layer separates readily from the cones1 there may be a difference in physical properties4 ,with ,congo red the upper part of the light line was only very slightly stained1 but aniline blue had a more pronounced effect4 ,the microchemical tests applied to the seed coat show that in the region above the light line there is only a slight trace of cutin or suberin1 but a considerable amount of cellulose and pectose4 ,all cell walls below the light line are mainly cellulose but contain some pectose4 ,the upper portion of the light line contains callose1 but the remainder of the light line appears to be chemically different from all other parts of the seed coat or else so dense as to resist the attack of the reagents4 ,,the ,,seed ,,coat ,,in ,,relation ,,to ,,the ,,absorption ,,of ,,water4 ,a study of permeable seeds soaked in water containing stains showed that there were no local regions through which the water passed4 ,the stains passed through all regions of the seed coat4 ,coating the micropylar region with vaseline retarded germination1 but had no effect upon the percentage of germination at the end of three days4 ,in seed coats through which the stain had passed1 the light line was not stained4 ,some stain was found in the canals which crossed the light line1 and much more in the cell cavities4 ,there was no evidence that the stain had permeated the substance of the light line4 ,it was able to cross the light line only when pores were present4 ,in impermeable seeds the stains passed readily to the light line4 7,pl4 ,v1 fig4 #g47 ,it was evident that the absorption of water was not prevented by either the cuticularized layer or the cone-shaped structures of the ,malpighian layer1 but by the light line4 ,the region outside of the light line became stained in a few hours1 but there was no trace of the stain within the light line after the seeds had remained a week in the stains4 ,alcohol did not penetrate the seed coat more readily than water4 ,a ,,comparison ,,of ,,permeable ,,and ,,impermeable ,,seed ,,coats4 ,no difference in chemical structure was found between the coats of permeable and impermeable seeds4 ,the principal differences were in the character and amount of thickening of the cell walls4 ,in many of the permeable seeds some of the canals were found to extend across the light line1 but this was not true for all permeable seeds4 7,pl4 ,v1 fig4 #h47 ,oblique sections of permeable seed coats showed that the cell cavities1 although reduced to mere pores by the thickening of their radial walls1 extended across the light line into the base of the cones1 thus forming a passageway through which the stains passed to the larger portions of the cell cavities below the light line4 7,pl4 ,v1 fig4 #d47 ,in the coats of the impermeable seeds the light line was usually broader1 the ,malpighian cells thickened more below the light line1 and the main cavities of the ,malpighian cells were more reduced and farther below the light line than in the coats of permeable seeds4 7,pl4 ,v1 fig4 #f47 ,no canals except occasionally a few very small ones were seen crossing the light line in impermeable seeds4 ,cross and oblique sections showed that the lumina of the ,malpighian cells were closed in the region of the light line4 ,thus it was found that permeable and impermeable seeds differ mainly in the amount of thickening which occurs in the walls of the ,malpighian cells4 ,in the impermeable seeds the thickening which begins at the outer tangential wall of the ,malpighian cell extends farther toward the inner tangential wall1 leaving the cell lumina smaller and farther below the light line than in permeable seeds4 ,the thickening is also more complete in impermeable seeds1 leaving fewer and smaller canals across the light line as well as closing the cell lumina in the region of the light line4 ,,the ,,action ,,of ,,sulphuric ,,acid ,,on ,,the ,,coats ,,of ,,impermeable ,,seeds4 ,impermeable seeds were soaked in concentrated sulphuric acid 7sp4 gr4 #a4hd7 for #ae1 #cj1 and #fj minutes2 then washed and put in the staining solutions4 ,after they had swollen1 they were removed from the staining solutions1 dried1 and embedded in glycerin gum4 ,a study of these seeds showed that the acid had eaten away all of the material outside of the light line and that the stain had passed through all regions of the seed coat4 7,pl4 ,v1 fig4 #aj47 ,when observed under the microscope1 it was seen that the action of the acid was rapid1 destroying the cuticle1 cuticularized layer1 and cones in about #e minutes4 ,after #ae minutes treatment with acid the light line1 aside from the presence of canals and pores not previously visible1 seemed to be very little affected4 ,the division lines along which the lateral walls of the ,malpighian cells were joined now became much more distinct across the light line1 thus indicating that there was some swelling in this region4 ,when a close examination of the path of the stain was made the cell lumina1 and occasionally very small pores1 were found to extend across the light line4 ,the presence of the stain in the pores indicated that they were paths of the stain across the light line4 ,some of the stain passed along the lines between cells and through the occasional canals crossing the light line1 but judging from the intensity of the stain in the lumina the canals appeared to be the principal passageways4 ,the action of the acid in opening the cell cavities across the light line was not determined4 ,it may be due to the swelling of the light line or to the removal of substances closing the pores4 ,no seeds were exposed to the acid for longer than an hour1 but at the end of this period the light line was still intact4 ,as compared with other portions of the ,malpighian layer1 it is extremely resistant to concentrated sulphuric acid4 ,since all cell walls below the light line are mainly cellulose1 the resistance of the light line prevents the acid from destroying the entire seed coat and reaching the embryo4 ,,literature ,,cited4 7#a7 ,beck1 ,gunther4 #ahgh4 ,vergleichende ,anatomie der ,samen von ,vicia und ,ervum4 ,in ,sitzber4 ,k4 ,akad4 ,wiss4 ,vienna1 ,math4 ,naturw4 ,kl41 ,bd4 #gg1 ,abt4 #a1 p4 #ede-egi1 #b pl4 7#b7 ,bergtheil1 ,c1 and ,day1 ,d4 ,l4 #aijg4 ,on the cause of hardness in the seeds of ,indigofera arrecta4 ,in ,ann4 ,bot41 v4 #ba1 no4 #ha1 p4 #eg-fj1 pl4 #g4 7#c7 ,crocker1 ,william4 #aijf4 ,role of seed coats in delayed germination4 ,in ,bot4 ,gaz41 v4 #db1 no4 #d1 p4 #bfe-bia1 #d fig4 ,literature cited1 p4 #bij-bia4 7#d7 ,darwin1 ,charles4 #ahhe4 ,the effects of cross and self fertilisation in the vegetable kingdom4 #dhb p4 ,new ,york4 7#e7 ,ewart1 ,alfred ,j4 #aijh4 ,on the longevity of seeds4 ,in ,proc4 ,roy4 ,soc4 ,victoria1 v4 #ba1 pt4 #a1 p4 #a-bjc4 ,literature1 p4 #c-d4 7#f7 ,gola1 ,guiseppe4 #aije4 ,ricerche sulla biologia e sulla fisiologia dei semi a tegumento impermeabile4 ,in ,mem4 ,r4 ,accad4 ,sci4 ,torino1 s4 #b1 t4 #ee1 p4 #bcg-bgj1 #a pl4 7#g7 ,haberlandt1 ,g4 #ahgg4 ,ueber die ,entwickelungsgeschichte und den ,bau der ,samenschale bei der ,gattung ,phaseolus4 ,in ,sitzber4 ,k4 ,akad4 ,wiss4 ,vienna1 ,math4 ,naturw4 ,kl41 ,bd4 #ge1 ,abt4 #a1 p4 #cc-dg1 #b pl4 ,hanstein1 ,johannes4 7#h7 #ahfc4 ,erluterung des ,nardoo genannten ,nahrungsmittels der ,urbewohner ,australiens1 einer ,marsilea-,frucht1 nebst ,bemerkungen zur ,entwicklung dieser ,gattung4 ,in ,monatsber4 ,k4 ,preuss4 ,akad4 ,wiss4 ,berlin1 #ahfb1 p4 #ajc-aai1 #a pl4 7#i7 #ahff4 ,pilulariae globuliferae generatio cum ,marsilia comparata4 #af p4 ,bonnae4 ,dissertation4 ,harrington1 ,george ,t4 7#aj7 #aiae4 ,hard clover seed and its treatment in hulling4 ,u4 ,s4 ,dept4 ,agr41 ,farmers' ,bul4 #fgf1 #h p4 7#aa7 #aiaf4 ,agricultural value of impermeable seeds4 ,in ,jour4 ,agr4 ,research1 v4 #f1 no4 #bj1 p4 #gfa-gif1 #f fig41 pl4 #ajf4 ,literature cited1 p4 #gif4 7#ab7 ,harz1 ,c4 ,d4 #ahhe4 ,landwirtschaftliche ,samenkunde4 #acfb p41 #bja fig4 ,berlin4 7#ac7 ,hiltner1 ,l4 #aijb4 ,die ,keimungsverhltnisse der ,leguminosensamen und ihre ,beeinflussung durch ,organismenwirkung4 ,in ,arb4 ,k4 ,gesundheitsamte1 ,biol4 ,abt41 ,bd4 #c1 ,heft #a1 p4 #a-ajb1 #d fig4 7#ad7 ,hughes1 ,h4 ,d4 #aiae4 ,making legumes grow4 ,in ,farm and ,fireside1 v4 #ch1 no4 #ai1 p4 #g1 illus4 7#ae7 ,huss1 ,mathias4 #ahij4 ber ,quellungsunfhigkeit von ,leguminosensamen und ,mittel zu deren ,abhilfe4 #gc p4 ,halle4 ,dissertation4 7#af7 ,junowicz1 ,r4 #ahgh4 ,die ,lichtlinie in den ,prismenzellen der ,samenschalen4 ,in ,sitzber4 ,k4 ,akad4 ,wiss4 ,vienna1 ,math4 ,naturw4 ,kl41 ,bd4 #gf1 ,abt4 #a1 p4 #cce-ceb1 #b pl4 7#ag7 ,kerner von ,marilaun1 ,anton4 #ahia4 ,pflanzenleben4 #b ,bd4 ,leipzig4 7#ah7 ,kirchner1 ,o4 #aije4 ber die ,wirkung der ,selbstbestubung bei den ,papilionaceen4 ,in ,naturw4 ,ztschr4 ,land-u4 ,forstw41 ,jahrg4 #c1 ,heft #a1 p4 #a-af2 ,heft #b1 p4 #di-fd2 ,heft #c1 p4 #ig-aaa4 ,literatur-verzeichnis1 p4 #aaj-aaa4 7#ai7 ,knuth1 ,paul4 #aijf-h4 ,handbook of flower pollination1 based on ,hermann ,mller's work upon ,the fertilisation of flowers by insects1 transl4 by ,j4 ,r4 ,ainsworth ,davis4 #c v41 illus4 ,oxford4 ,bibliography1 v4 #a1 p4 #bab-chj4 7#bj7 ,lohde1 ,georg4 #ahgd4 ,ueber die ,entwicklungsgeschichte und den ,bau einiger ,samenschalen4 #db p41 #a pl4 ,naumburg4 ,dissertation4 7#ba7 ,love1 ,harry ,h41 and ,leighty1 ,clyde ,e4 #aiab4 ,germination of seed as affected by sulphuric acid treatment4 ,n4 ,y4 ,cornell ,agr4 ,exp4 ,sta4 ,bul4 #cab1 p4 #bic-ccf1 fig4 #gh-he4 7#bb7 ,lutts1 ,f4 ,m4 #aiag4 ,sweet clover1 advantages of the crop for soil improvement4 ,in ,ohio ,agr4 ,exp4 ,sta4 ,mo4 ,bul41 v4 #b1 no4 #b1 p4 #de-dg1 illus4 7#bc7 ,malpighi1 ,marcello4 #afhg4 ,opera omnia1 seu thesaurus locupletissimus botanico-medico-anatomicus 444 ,new ed4 #b v41 pl4 ,lugduni ,batavorum4 7#bd7 ,marlire1 ,h4 #ahig4 ,sur la graine et spcialement sur l'endosperme du ,ceratonia siliqua4 ,in ,cellule1 t4 #ac1 fasc4 #a1 p4 #e-fj1 #b pl4 7#be7 ,martin1 ,j4 ,n4 #aiae4 ,relation of moisture to seed production in alfalfa4 ,iowa ,agr4 ,exp4 ,sta4 ,research ,bul4 #bc1 p4 #cja-cbd1 #b fig4 7#bf7 ,mettenius1 ,georg4 #ahdf4 ,beitraege zur ,kenntniss der ,rhizocarpeen4 #fe p41 #c pl4 ,frankfurt am ,main4 7#bg7 ,die ,hohenheimer ,samenritzmachine4 #ahid4 ,in ,braunschweig4 ,landw4 ,ztg41 ,jahrg4 #fb1 ,nr4 #ai1 p4 #hf4 illus4 7#bh7 ,mller1 ,hermann4 #ahhc4 ,the fertilisation of flowers1 transl4 by ,d',arcy ,w4 ,thompson4 #ffi p41 #ahf fig4 ,london4 ,bibliography1 p4 #eii-fcj4 7#bi7 ,nobbe1 ,friedrich4 #ahgf4 ,handbuch der ,samenkunde4 #fca p41 #cci fig41 #a pl4 ,berlin4 7#cj7 --------1 and ,haenlein1 ,h4 #ahgg4 ,ueber die ,resistenz von ,samen gegen die usseren ,factoren der ,keimung4 ,in ,landw4 ,versuchs ,sta41 v4 #bj1 p4 #ga-if1 #ac fig4 ,pammel1 ,l4 ,h4 7#ca7 #ahii4 ,anatomical characters of the seeds of ,leguminosae1 chiefly genera of ,gray's ,manual4 ,in ,trans4 ,acad4 ,sci4 ,st4 ,louis1 v4 #i1 p4 #ia-bge1 pl4 #g-ce4 ,bibliography1 p4 #bbd-beg4 7#cb7 #ahhf4 ,on the structure of the testa of several leguminous seeds4 ,in ,bul4 ,torrey ,bot4 ,club1 v4 #ac1 no4 #b1 p4 #ag-bd1 pl4 #eb-ec4 7#cc7 ,rees1 ,bertha4 #aiaa4 ,longevity of seeds and structure and nature of seed coat4 ,in ,proc4 ,roy4 ,soc4 ,victoria1 n4 s41 ,v4 #bc1 pt4 #b1 p4 #bic-dad1 pl4 #gi-ha4 7#cd7 ,russow1 ,edmund4 #ahgb4 ,vergleichende ,untersuchungen betreffend die ,histiologie 7,histiographie und ,histiogenie7 der vegetativen und sporenbildenden ,organe und die ,entwickelung der ,sporen der ,leitbndel-,kryptogamen1 mit ,bercksichtigung der ,histiologie der ,phanerogamen1 ausgehend von der ,betrachtung der ,marsiliaceen4 ,in ,mm4 ,acad4 ,sci4 ,st4 ,petersb41 s4 #g1 t4 #ai1 no4 #a1 #bjg p41 #aa pl4 7#ce7 ,schleiden1 ,m4 ,j41 and ,vogel1 ,j4 ,r4 ,th4 #ahdb4 ber das ,albumen1 inbesondere der ,leguminosen4 ,in ,nova ,acta4 ,acad4 ,caes4 ,leop4 ,carol4 ,nat4 ,cur41 v4 #ai1 pt4 #b1 p4 #ea-if1 pl4 #dj-de4 ,reprinted4 7#cf7 ,sempolowski1 ,anton4 #ahgd4 ,beitraege zur ,kenntniss des ,baues der ,samenschale4 #eg p41 #c pl4 ,leipzig4 ,dissertation4 7#cg7 ,tietz1 ,a4 ,o4 ,q4 #ahgf4 ber die ,keimung einiger ,coniferen und ,laubhlzer bei verschiedenen aber constanten ,temperaturen4 #dd p41 #h pl4 ,reudnitz-,leipzig4 ,dissertation4 7#ch7 ,tunmann1 ,o4 #aiac4 ,pflanzenmikrochemie4 #fca p41 #acg fig4 ,berlin4 7#ci7 ,verschaffelt1 ,e4 #aiab4 ,le traitement chimique des graines imbibition tardive4 ,in ,rec4 ,trav4 ,bot4 ,nerl41 v4 #i1 livr4 #d1 p4 #dja-dce4 7#dj7 ,westgate1 ,j4 ,m41 and ,coe1 ,h4 ,s4 #aiae4 ,red clover seed production3 ,pollination studies4 ,u4 ,s4 ,dept4 ,agr4 ,bul4 #bhi1 #ca p41 #g fig4 ,literature cited1 p4 #bi-ca4 7#da7 ,wettstein1 ,richard von4 #ahhh4 ,beobachtungen ber den ,bau and die ,keimung des ,samens von ,nelumbo nucifera ,grtn4 ,in ,verhandl4 ,k4 ,k4 ,zool4-,bot4 ,gesell4 ,wien1 ,bd4 #ch1 p4 #da-dh1 pl4 #a4 7#db7 ,white1 ,jean4 #aijh4 ,the occurrence of an impermeable cuticle on the exterior of certain seeds4 ,in ,proc4 ,roy4 ,soc4 ,victoria1 v4 #ba1 n4 s4 pt4 #a1 p4 #bjc-baj1 #b pl4 7#dc7 ,wigand1 ,albert1 and ,dennert1 ,e4 #ahhh4 ,nelumbium speciosum ,w4 ,eine monographische ,studie4 #fh p41 #f pl4 ,cassel4 7,bibliotheca ,botanica1 ,heft #aa47 7#dd7 ,young1 ,w4 ,j4 #aijf4 ,the embryology of ,melilotus alba4 ,in ,proc4 ,ind4 ,acad4 ,sci4 #aije1 p4 #acc-ada1 #ej fig4 ,bibliography1 p4 #acf4 ,,additional ,,copies ,,of ,,this ,,publication ,,may ,,be ,,procured ,,from ,,the ,,superintendent ,,of ,,documents ,,government ,,printing ,,office ,,washington1 ,d4 ,c4 ,,at #ae ,,cents ,,per ,,copy 99 99 99 99 99 ,transcriber ,note ,minor typos may have been corrected4 ,illustrations were moved to prevent splitting of paragraphs4 ,content produced from files generously provided by the ,,usda through ,the ,internet ,archive and all resultant files are placed in the ,public ,domain4