SCIENCE 



NEW YORK, JUNE 23, 1893. 



(Sttitzzelle or Tiagerin — b^). To make this more intelligible, the 

 author's diagram is inserted here: — 



A STUDY ON PLANT FECUNDATION. 



BY H. J. WEBBER, SUBTROPICAL LABORATORY, EUSTIS, PLA. 



The phenomena of fecundation in obscure plants are in them- 

 selves probably uninteresting to the general reader. In so far, 

 however, as they bear on the problem of heredity, which has 

 been popularized by the works of Weismann and others, they be- 

 come of interest to a wide circle of readers and thinkers. This 

 extended interest makes it desirable that the results of important 

 studies should be brought to general notice. 



In the study of fecundation in plants, the most important works 

 which have appeared for several years are the studies of Guig- 

 nard ' and Treub.^ These have been summarized in the Botanical 

 Gazette and American Naturalist. 



Shortly after the publication of Guignard's studies there ap- 

 peared a study by Klebahn ' on the " Fructification of CEdogonium 

 Boscii," an alga of which numerous relatives occur in our Ameri- 

 can ponds. The article is in no sense revolutionary, yet contains 

 much of interest and value. 



A discussion of the occurrence of polar bodies in plants occu- 

 pies a large part of the paper. This was true also of Guignard's 

 paper mentioned above. Zoologists found polar bodies to be a 

 very general, if not universal, accompaniment of the animal egg, 

 and they came to be looked upon as having an important role in 

 the process of fecundation. Botanists now, it appears, discovered 

 that in order to make the theories correspond they must find 

 polar bodies in plants. Following this apparent necessity, for 

 years, every fragment of protoplasm, every small cell or nucleus, 

 anywhere in the region of the egg-cell, for which no other use 

 could be positively affirmed, has been diligently pointed out as 

 probably having the function of polar bodies. To clear up this 

 probable rubbish must now occupy a great share of the attention 

 of botanists writing on related subjects. 



Klebahn's study was completed before the publication of Guig- 

 nard's article demonstrating the presence of .attractive spheres 

 (asters) in plants, hence this interesting feature in fecundation is 

 not mentioned. 



In the male filament the nucleus lies in the upper end of the 

 ceU, the cap end, where the ring and the disunion in the mem- 

 brane form. In mitosis the upper cell, forming the antheridium, 

 receives only a small amount of protoplasm with the nucleus. 

 After this mitosis the lower nucleus returns to the resting stage, 

 still remaining in its old position, and shortly passes to a new 

 mitosis. This role is continued till the n umber (four or five) of 

 antheridium cells are formed. The sterile remainder of the 

 mother cell, after the last mitosis, remains as the lower cell of 

 the series. The protoplast of each antheridium cell divides into 

 two portions, which become the antherozoids. The nuclei of 

 the antherozoids are smaller than those of the vegetative or female 

 cells and have no apparent nucleolus. 



In the formation of the oogone a cell of the female filament di- 

 vides into two daughter cells, an under (a) and an upper (&). 

 These two daughter cells divide again, producing four cells (a j, 

 Oj, 61, 62). The upper one of these (bj) is the oogonium mother 

 cell. This divides again, and the upper daughter cell of this divi- 

 sion is the oogonium (B), and the lower the supporting cell 



' Leon Gulgnard, " Nouvelles Etudes sur la Fecondation," Ann. des Scl. 

 NatureUes Bot., xlv. (1891), pp. 163-288. 



> M. Treub, " Sur les Casuarinees et leur place dana le Syst^me Naturel,'i 

 Ann. du Jardlu Bot. de Bultenzorg, i., pp. 145-231. 



5 H. Klebahn, " Studlen uber Zygoten. II., Die Befruolitung von (Edogonlum 

 BOBCll," Prlngshelma Jahr. fur wlssenschaflltcbe Botanlk.," Bd. xxlv., pp. 

 235-267, 1 Taf. 



«! tta bi 63 B 



In most cases four sterile cells accompany each oogone, but 

 occasionally the cell (a,) becomes also an oogonium mother cell, 

 the division of which forms an oogonium, A, and its supporting 

 cell (Oj). In this case only two sterile cells accompany each 

 oogone. 



The nucleus of the oogonium (B) and of the oogonium mother 

 cell (&2) are of about the same size and constitution as the nuclei 

 of the vegetative cells. The difference between the nuclei of the 

 oogonium and of the sterile accompanying cells, (6j) and (63), is 

 of especial interest. In the latter the nuclei are much smaller 

 and the nucleolus is always absent. The author especially en- 

 deavored to count the number of chromatin bands passing to each 

 nucleus, hoping to obtain some light on Weismann's theoretic 

 reducing division supposed to occur in the formation of the polar 

 bodies. Unfortunately it was found impossible to be sure of the 

 number. 



After the oogone has taken its definite form, an opening forms 

 in the upper part for the entrance of the antherozoids. The open- 

 ing, however, remains closed by an especially developed mem- 

 brane until the protoplasm of the oogonium draws together into 

 the mature egg-cell ready for fecundation. The nucleus of the 

 oogone meanwhile lies in the upper part of the egg-cell near the 

 point of activity, without, however, dividing or in any evident 

 way giving off substance. The closing membrane now disappears, 

 leaving the way open for the entrance of the antherozoids. Of 

 the numerous cases examined, in no place was anything observed 

 indicating a separation or throwing off of any part of the proto- 

 plasm or nucleus. On the contrary, the closing membrane is still 

 present when the protoplast of the oogonium draws together. 

 Nothing in the opening process of the oogonium of this species 

 can be analogized to the formation of polar bodies, and in no 

 stage in the course of fecundation and maturation of the oogone 

 is there anything similar developed. 



The antherozoids, passing through the opening in the wall of 

 the oogonium, approach the egg, one fusing with it. Before 

 fusing with the egg-nucleus the male nucleus enlarges from 

 about four to six /i. No other change in structure is noticeable. 

 After the fusion of the nuclei has taken place, the fecundated 

 nucleus is still easy to recognize ; the coarser chromatin elements 

 of the male nucleus still forming a well differentiated group. 

 Very soon, however, these marks disappear, the male chromatin 

 becoming distributed till it is wholly unrecognizable. The nu- 

 cleus of the egg is finally only slightly more strongly granular 

 than the unfecundated. Many antherozoids enter the oogone 

 cavity, but only one enters the egg. Eleven were counted in one 

 case in an oogonium cavity. 



The author reviews at considerable length the probable cases of 

 polar bodies in plants, mentioned in literature. Jhe conclusion 

 reached is that at least they do not possess the importance and 

 necessary role in plants that is assigned to them in the animal 

 kingdom. 



It may be possible that in CEdogonium boscii the two cells, &i 

 and &,, accompanying the oogonium are to be considered the 

 equivalents of polar bodies. These, with the oogone (B), are de- 



