MUSEUM OF COMPARATIVE ZOOLOGY. 387 



plate and cellulose membrane are formed. He says (p. 28) : "(1.) The 

 cell plate, formed in the ' cask ' between the two young nuclei, grows 

 at its edges until it touches the walls of the cell on all sides. (2.) Never 

 have I seen the cell plate formed in the cask completed by a ring ema- 

 nating from the cell wall ; neither have I ever seen an annular membrane 

 of cellulose rise up to encounter the cell plate." Thus the role of the 

 nucleus is much more important than Strasburger admits. It is by the 

 direct intervention of the young nuclei that the whole cell plate, and 

 consequently the whole of the cellulose membrane, is formed. 



From a consideration of all his own observations he concludes that 

 the filaments and striations in or between the nuclei (nuclear fibres and 

 interzonal filaments) are of secondary importance, at least in the cell 

 division of the higher plants. 



2. Maturation. 



The fate of the germinative vesicle has been a matter of ardent dis- 

 cussion since 1850, yet it is only within a very recent period that suffi- 

 ciently varied methods of investigation have been employed to make the 

 attainment of a final decision probable. But increased facilities of study 

 have not led to unanimity of opinion among those who have carefully 

 followed the changes which overtake this structure. 



It is now very generally conceded that the germinative vesicle, like 

 the nucleus of an ordinary cell,* suffers a remarkable metamorphosis. 

 By some observers this metamorphosis is claimed to be only a rather 

 fundamental rearrangement of the constituents of the vesicle, without 

 their general dispersion ; by others, that it is so radical as really to in- 

 volve a total dissolution and a distribution of the nuclear matter. To 

 this latter conception the term metamor'phosis can be applied only in its 

 broadest sense ; on the other hand, the first conception is not held to 

 entirely preclude either the loss of old, or the acquisition of new matter 

 in the process of transformation. 



* A general discussion of the morphological value of the germinative vesicle can- 

 not be attempted here, especially since the origin and growth of the ^gg^ which has 

 formed no part of my studies, must of necessity constitute an important portion of the 

 evidence to be considered in such a discussion. I may state, however, in this connec- 

 tion, that quite recently a view, which at one time obtained ver}'' general acceptance, 

 has been revived by Brandt, Villot, and others. They claim that the germinative 

 vesicle is entitled to rank as a cell rather than as a nucleus. 



Without attempting to refute at length their position, I wish to empliasize the fact 

 that the germinative vesicle sustains the same relation to the first maturation spindle 

 that an ordinary nucleus does to the sjnndle which takes its place. 



