IMAGE EVALUATION TEST TARGET (MT-3) 1.0 1.1 ^|2£ |25 m 2.2 Its tli 1 40 12.0 1^ lll'-^ II '-6 < 6" ». Hiotographic Sciences Corporation 23 WfST MAIN STRIET WIBSTM.N.Y. MSUd (716;S72-4S03 '^ ,> Us CIHM/ICMH Microfiche Series. CiHIVi/ICIViH Collection de microfiches. Canadian Institute for Historical Microreproductions / Institut Canadian de microreproductions historiques ihhhA Tachnicai and Bibliographic Notaa/Notaa tachniquaa at bibliographiquaa Tha Inatituta haa anamptad to obtain tha baat original copy availabia for filming. Faaturaa of thia copy wliicti may ba bibliographieally uniqua. which may altar any of tha imagaa in tha raproduction. or which may significantly changa tha uaual mathod of filming, ara ehackad balow. HColourad covara/ Couvartura da coulaur rn Covafa damagad/ D D EZ] D a Couvartura andommag^ Covara raatorad and/or laminatad/ Couvartura raataurAa at/ou paiiiculAa r~~1 Covar titia miaaing/ La titra da couvartura manqua □ Colourad mapa/ Cartaa giographiquaa mn coulaur Colourad ink (i.a. othar than blua or black)/ Encra da coulaur (i.a. autra qua blaua ou noira) I — I Colourad plataa and/or iiluatrationa/ D Planchaa at/ou iiluatrationa an coulaur Bound with othar matarial/ Ralii avac d'autraa documanta Tight binding may cauaa shadowa or diatortion along intarior margin/ La rB liura sarria paut cauaar da I'ombra ou da la diatorsion la long da la marga intAriaura Blank laavas addad during rastoration may appaar within tha taxt. Whanavar possibia, thasa hava baan omittad from filming/ II aa paut qua cartainaa pagas blanchas ajoutias lora d'una raatauration apparaiaaant dana la taxta, mais, toraqua cala Atait posaibia, caa pagaa n'ont paa «t« film^aa. 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Las details da cat axamplaira qui sont paut-Atra uniquas du point da vua bibliographiqua. qui pauvant modifiar una imaga raproduita. ou qui pauvant axigar una modification dana la mithoda normala da filmaga sont indiquia ci-daaaoua. rn Colourad pagaa/ n Pagaa da coulaur Pagaa damagad/ Pagaa andommagiaa Pagaa raatorad and/oi Pagaa raataurAas at/ou palliculias Pagaa discolourad. stainad or foxa< Pagaa dicolortes. tachattes ou piques Pagaa datacnad/ Pagaa ditachtos Showthrough/ Tranaparanca Quality of prin Quality inigala da I'imprassion Includaa supplamantary matarii Comprand du matirial supplimantaira Only adition availabia/ Saula Mition disponibia pn Pagaa damagad/ pn Pagaa raatorad and/or laminatad/ r~7] Pagaa discolourad. stainad or foxad/ r~n Pagaa datacnad/ r~7 Showthrough/ |~n Quality of print variaa/ rn Includaa supplamantary matarial/ I — I Only adition availabia/ Pagaa wholly or partially obscured by errata slips, tissuaa. etc.. hava baan rafilmed to ensure the best possible image/ Lea pages totalement ou partieilement obscurcies par un fauillet d'errata. una pelure. etc., ont itt filmies k nouveau da faqon d obtanir la mailleure image possible. This item is filmed at tha reduction ratio checked below/ Ce document eat film* au raux da rMuction indiqu* ci-deaaoua. 10X 14X 18X 22X 26X 30X y 12X lex aox 24X 28X 32X Th« copy fiimMl h«r« has lM«n r«produc«d thanks to ths gsnsrosity of: New Brunswick MuMum Saint John L'sxamplairs filmi fut rsproduit grl^ea i la fljinirosit* da: Now Brunswick IMuscum Saint John Tha imagas appaaring hara ara tha bast quality possibia eonsidaring tha condition and lagibillty of tha original copy and in kaaping with tha filming contract spacificationa. Laa imagaa suhrantaa ont 4ti raproduitas avac la plua grand soin, eompta tanu da la condition at da la nattatA da raxamplaira filmA. at •» conformity avac laa condltiona du eontrat da filmaga. Original copiaa in printad papar eovars ara filmad baginning with tha front covar and anding on tha last paga with a printad or illuatratad impraa- sion, or tha back covar whan appropriata. All othar original copiaa ara filmad baginning on tha first paga with a printad or illuatratad impraa- sion, and anding on tha laat paga with a printad or iliustrstad imprassion. Laa axampiairaa originaux dont la couvartura an papiar aat imprimte sont fiimis an commandant par la pramlar plat at an tarminant soit par la damiira paga qui comporta una amprainta d'Impraasion ou d'illustration, soit par la sacond plat, salon la cas. Tous las autras axampiairaa originaux sont filmto an commandant par la pramlAra paga qui comporta una amprainta dlmpraaaion ou d'illuatration at •n tarminant par la darniAra paga qui comporta una talla amprainta. Tha laat racordad frama on aach microficha shall contain tha symbol —^(moaning "CON- TINUED"), or tha symbol y (moaning "END"), whichavar appiiaa. Un daa symbolaa suivants apparaftra sur la darniAra imaga da chaqua microficha. salon la caa: la symbols — »• signifia "A SUiVRE". la symbols ▼ signifia "FIN". Mapa. plataa. cliarts. ste.. may ba filmad at diffarant raduction ratioa. Thoaa too larga to ba antiraly includad In ona axpoaura ara filmad baginning in tha uppar laft hand comar, laft to right and top to bottom, aa many framaa aa raquirad. Tha following diagrama illustrata tha mathod: Laa cartaa. planchaa. tabiaaux. ate. pauvant Atra filmte A daa taux da reduction diffirants. Loraqua la documant ast trop grand pour Atra raproduit an un saul clichA. il ast filmA k partir da I'angia aupAriaur gaucha. da gaucha k droita. at da haut an bas. an pranant la nombra d'imagas nAcassaira. Las diagrammas suivants illustrant la mAthoda. 1 2 3 1 2 3 4 5 6 ' ii I " ' Hi' I !' I i, III 1 VOLUME XX\ BOT UPON POL Many cas widely separa in i860, rec thirteen gene Strasburger w logical basis, tions have be notably Dode frey (1895), works, in so f marized belov bryony hithe which Engelr figured {p/. 2^ case was cite suggests that in Opittiiia gin hence polyene explained as this family, I embryonic, at VOLUME XXV NUMBER 4 Botanical Gazette APRIL 1898 ^6%^^.X,f&ff,CSt^, upon polyembryony and its morphology opuntia vulgaris. \V. F. G A N O N (i. in kmyLtJ^ (with plate XVI ) Many cases of polyembryony are now known, occurring in widely separated groups, Braun, in his summary of the subject in i860, recorded twenty-one cases in twelve families and thirteen genera, which number has been added to by others. Strasburger was the first to thoroughly investigate its morpho- logical basis, and since his paper in 1878 important contribu- tions have been made to the subject by several investigators, notably Dodel (1890), Overton ( 189 1 ), Tretjakow (1895) , Jef- frey (1895), ^^^ Hegelmaier (1897). The results of these works, in so far as they touch this subject, will be found sum- marized below. In the Cactaceae, the only case of polyem- bryony hitherto known has been that of Opuntia tortispitta, which Engelmann, in his Cactace.t of Whipple's expedition figured (//. 2j,fig.4^ as having two embryos in one seed. This case was cited by Braun (p. 155, //. 5, figs. 18-20), who also suggests that the four cotyledons which he had himself noticed in Opuntia glaucophylla may indicate a fusion of two embryos and hence polyembryony, though he points out that it may also be explained as fasciation. While studying the seedling stages in this family, I have found that Opuntia vulgaris is markedly poly- embryonic, and I may here add that although I have worked 221 222 BOTANICAL GAZETTE [aI'RII. over the seedlings of some seventy-five species in this family I have seen no other case of it. The plants from which my seeds were taken have been grow- ing and flowering luxuriantly for at least four years in the Botanic Garden of Smith College. They agree with the char- acters given in books for that species, but the source from which they came into the garden is unknown. They set seed every year in great abundance. When the seeds are planted, from many, perhaps a half, of them more than one seedling comes up, and there is the greatest variation in the number, size, and degrees of union with one another of these seedlings. This variety is best made evident by the figs, i to 5, typical cases drawn the natural size, and of course there are all stages between. I have not tried to follow them further, but what 1 have noticed seems to show that the larger of a set crowds out the others. It is now important to ascertain the morphological origin of this polyembryony. The ovule of Opuntia vulgaris is at first amphitrcpous, but in its development it becomes elongated and bent, at the same time turning around in such a way that the funiculus makes a complete turn around it, so that finally it simulates a cam- pylotropous condition {fig. 6). Its development in other spe- cies of this genus, together with the development of other species of other genera in this family, has been described by d'Hubert, and his account fits this species fairly well. Inside of the funiculus are the integuments, made up of three distinct layers of cells, and inside of these is a nucellus, which becomes absorbed, except for a small portion (at x,fig. 6), by the embryo as the seed ripens. Finally there is the distinct embryo sac, in which there forms after fertilization an abundant endosperm, which consists of protoplasts without cellulose walls, the whole of course absorbed by the growing embryo. In ripe seeds one finds usually a large embryo nearly filling it, with others much smaller and pressed to one side. In half- ripe seeds one finds such a condition as is shown in fig. 8, where there is one larger embryo with several smaller ones, and usually 1898.1 POLYEMBRYON.Y AND ITS MORPHOLOGY 223 the larger comes not from the microj)ylar extremity of the embryo sac, but from some point on its wall a little removed. In other cases one sees a single embryo springing from the micropylar end and one or more from the walls, as '\vi fig. 7. Or again, though rarely, there is a single embryo at the micropylar end, as in fig. g. There is a close resemblance between these figures and those given by Strasburger for Citrjis Aurantium {fig. jy). If now these be examined in a still younger stage, it becomes clear thcit the embryos come from two different posi- tions : first, from a rather irregular mass of tissue which lies at the micropylar end of the embryo sac, and extends thence along its wall ; and second, directly from the wall itself. Both of these conditions are well shown in fig. 10. It is imjjortant to notice, however, that some cases seeming to belong to the latter category belong really to the former, as is illustrated hy fig. 1$, where the wall-standing embryos are shown to spring really from the mass at the micropylar end, but this is not the case with all of the wall-standing embryos, for sections show that in many cases, i. c^ fig. 10, these are entirely independent of that mass. It is probable that the irregular embryos come as a rule from the micropylar mass, while the regular ones are from the walls, for all I have seen in that position have regularly two cotyledons. So far, in tracing backwards the origin of the polyembryony, everything is plain, and it is easy to find plenty of cases such as are here figured. At this stage, the entire distinctness of the micropylar mass from the nucellus beneath {sec figs. 10 and //) and its close resemblance to that described and figured by Jef- frey which he traced to its origin in a fertilized egg cell, would lead one to suppose that we have here a similar case ; while in the wall-standing embryos, which are so sharply distinct from the nucellus {fig. 11) that an origin from nucellus seems excluded, only an origin from an endosperm cell would appear possi- ble, a condition which is yet unknown.' But the earlier stages show that both of these suppositions are incorrect. In a great ' This was my own opinion in both cases at the time this paper was read before tiii; 324 BOTANICAL GAZETTE [aI'KII. abundance of material which shows the ovules in all stages before and at the time of fertilization, and also all staji^es after that represented in fig, to, I was able to find, after prolonged and careful search, only three cases which show the origin of the embryos, but happily they leave no doubt on the subject. I think this stage must be passed through very rapidly, and per- haps at night, when none of my material was collected. In stages earlier than fig. lo, the pollen tube can usually be seen in the micropylar region of the nucellus, but an egg cell cannot be detected. Instead there regularly lies in its position a crumpled mass of protoplasm {fig. 12, 14, pr.), shrunken in my material by the weak alcohol used to preserve it. I think the egg cell disappears early in the development of the ovule, a point which will be cleared up by a complete study of the devel- opment of the embryo sac, now being made by one of my students. At all events there is certainly no egg cell present in any of my preparations at the period when the embryo building begins. The nucellus cells near the pollen tube arc rich in con- tents, and in one case {fig. 12) I have found these beginning to bud out into the embryo sac. That these represent the begin- ning of the formation of the micropylar mass, I think there can be no question. It is precisely in this way that the adventi- tious embryos originate in P'unkia and other cases, as described so fully and clearly by Strasburger. In another case {fig. /?) there are present not only the richly protoplasmic nucellus cells near the pollen tube, here, however, not budding, but also other nucellus cells a little removed and separated by a space filled with cells rather poor in contents; and these cells with rich con- tents are also distinctly budding out {fig. /?, x). Now these, I believe there can be no doubt, are the beginning of the wall- standing embryos ; it is quite probable that at first they are con- tinuous with those near the pollen tube, but are removed from them by the growth in length of the embryo sac, which at this time is very rapid. At all events they are nucellus cells. The Society for Plant Morphology and Physiology, Dec. 29, 1897. 1 had not then found the three cases next to be desciibed, which prove the origin to be different. 1898] POl.VEMfiRYOiVY AND ITS MORPHOLOGY til third case I have found is represented in fig. /./, which is more advanced thany?^. /j, and where the differentiation of the richly protoplasmic cells of the embryonic mass from the nearly empty cells beneath it is fairly sharp, but nevertheless the rela- tions of the two kinds are still sufficiently close to show the origin of the one from the other. Another section of the same specimen shows a similar connection of the other mass of embryonic tissue with the nucellus. From these cases it is clear that in this species the embryos of both positions arise from the nucellus, and in this respect agree with Funkia.Nothoscordum, Citrus, and others, the usual method. A synopsis of the modes of origin of polyembryony is given by Tretjakow, which in synopsis, with the additions made by others, and excluding cases due to branching of the nucellus, union of two ovules, presence of two or more embryo sacs in one nucellus, etc., are as follows : From cells of nucellus near the micropyle, Ftinkia and others (Strasburger) ; from a second egg cell, Santalum, or from its doubling Sinningin (Strasburgcr) ; from sy nergids. Mimosa Denhartii ( Guignard) , Iris Sibirica ( Dodel ) , and perhaps in Lilitim Martagon (Overton) ; from the antipodals and synergids. Allium odortim (Tretjakow) ; from the branching of a mass of tissue derived from the fertilized egg cell (Jeffrey) ; finally, Hegelmaier points out the occurrence in Allium odorum of embryos from e.^'g cell, synergids, antipodals and nucellus cells, all in the same species and individuals. There still remain as possible origins, endosperm and integument. In all known cases, except Ccelebogyne, the production of the new embryos takes place only after fertilization, or at all events after the entrance of the pollen tube. A question of great interest now arises as to the significance of polyembryony. Strasburger, though he mentions that it recalls apogamy, then recently discovered by Farlow, contents himself with referring to the extra embryos as " Adventivknos- pen" or "vegetative Adventivkeime." Pfeffer'' has suggested that it is but a case of budding, and that the specific conditions ' Pflanzenphysiologie i : 29. 1897. aa6 HO TANICAl. GA/.E TTE Iaprii. in the embryo sac determining the form of the sexually pro- duced embryo, jj[ive the same form to the adventitious embryos. Tretjakow suggests that the development from the antipodals represents a|)ogamy, the anti|)odals being homologous with the vegetative cells of the prothallus, but this explanation will not a[)ply to the origin from nucellus cells. Jeffrey has nothing to say on this point, while Ilegelmaier concludes his paper thus: Die vcrlialtiiissiniUsi^e Scltenhcit dcr deni Kinpparat cntspriiiK'ciuicn I'olycnibrvoiiie hci //. ottonim ciiierseits uiid das oftere ^elc^cntlichu Vor- koininen dicscr Form l)ei vcrschiedciicn andereii IMIaii/cn aiidercrseits koiintc viflleiclu y.ii dcr AufTasstin^ flUiren, class ihr V^)rkniiiiiieti bei unsercr I'tlan/e Uhcrhatipt nicht in dieselbe Kcihc niit dem V'orkoiiiinen dcr andercti Koriiicn von Folycnil)ryonic bei ihr zu stellcn iind ihr /iissannncntrcffcn mit diescn and- crcn Korincn mchr nur ein /ufiiiliges sei. Aber mindcstcns fUr diesc Ictzti-rcn ist doch wohl die Annahnie iinahweisbar, das irgcndwelchc gemcinschaftlichcn Ursachen vorhandcn sein miisscn, flir dercn Krkenntniss durch ein Spiel mit niorphologischen Honiologien nichts zu gewinncn sein wllrde. In general for a new feature one of three origins may be supposed. First, it may be some incidental growth or functional condition. Mere comes the explanation of budding, and Pfef- fer's explanation of the assumption of the embryo form through specific (jualitics of the embryo sac. But polyembryony seems too distinct and elaborate a process to be thus explained. Sec- ond, it may be a relic of some older condition now disappear- ing. Hut its very different morphological origins arc against this. Here comes its explanation as apogamy, but this does not explain the origin from the nucellus. Third, it may be the early stages in the development of something new. It can hardly yet be of any service to the plants, for many of the embryos are absorbed before the seeds are ripe, and in other cases usually but one develops, though perhaps one of the smaller may some- times take the place of the leader if this is destroyed. Its origin in several distinct groups and by several distinct methods seems to imply that there is some virtue in the development of the extra embryos, and that their appearance is controlled by that influence, whatever it may be, which is much more powerful than mere morphological inertia, and which elsewhere forms new I8q8] roi.YI.MHKYONY ANH ITS MOKniOl.OCY 327 Structures from the most different morphological origins. In its independent appearance in distinct group}" it is comparable with the appearance of heterospory, but whether polyembryony like heterospory will lead to some higher condition remains lo be seen, though we shall not see it. 6.MITH CoilKCK, NORIMAMI'TON, MASS. BIMLIOC.RAl'HY. Hkaun, a. — Ucber I'olycnibryonie und Keiimin>< von Cu-'lcboKyne. i860 IIkcki.maikk, F. — Zur Kenntnissilur I'olyenibryonie \v>\\ Allium oilorum L. Hot. Zeit. 55 : 133. i8y7. IIuiu:kt, K. I)'.- - Rechercbt's siir Ic sue cnibryoniiaire lasm of endiryo sac. Figs. i. 2, 3, 4, 5, each showing the embryos from a single seed, nat- ural size. Fui. 6. Median section through an ovule of Opuntia vult^niris, some- what diagrammatized, six times natural size:/- funiculus; a — attach- ment of funiculus to ovule ; .r = portion of nucellus not absorbed when seed is ripe. Fig. 7. Embryo sac showing three embryos, one from the micropylar end and two from the wall. X 18. F'iG. 8. Embryo sac showing one large embryo on the wall and several smaller from the micropylar end. X 18. Not a section, but a half seed laid open. 028 BOTANICAL GAZETTE [aprm. Fig. 9. Embryo sac showing a single embryo from the micropylar end. X 35- Fio. 10. Embryo sac showing embryos on the wall together with the branching mass from the micropylar end. Nucellar cells drawn nearly exactly ; those of embryos exact on the outside but only approximate in the interior. X go. Fig. II. An embryo on the wall; to show the connection of cells of embryo to those of nucellus ; a microtome section. X 90. Fig. 12. Beginning of budding from nucellus cells near the micropyle. X 90. Fig. 13. Cells of nucellus beginning to grow out at x into an embryo. X 90. Fig. 14. Embryonic mass separating from the nucellus. The section is cut diagonally through the apex of the embryo sac. X 90. Fig. 1 5. a, b. Two sections from one embryo sac to show that some apparently wall-embryos are really from the micropylar mass. X i8. BOTANICAL GAZETTE, XXV. PLATE XVL M GAXONG on POLYKMHRYOXV.