382 BULLETIN OF THE 



related to this process of free cell-formation, — which is to a certain ex- 

 tent intermediate between cell division and the latter. I refer to the 

 formation of nuclei (by division) in homogeneous masses of protoplasm 

 which do not at once (perhaps never) respond to the nuclear division by a 

 division of their substance, — e. g. segmentation in Eupagurus Prideauxii 

 (P. Mayer, '77). Such potential cells (autoplasts, Lankester ; entoplasts, 

 Whitman,) differ, as regards their origin, from the free-formed cells in 

 that their nuclei demonstrably arise by division. It seems to me not 

 impossible that the free cell-formation of botanists may ultimately be 

 found to be much more restricted than at present believed ; that it may 

 be possible, namely, to demonstrate the existence of stages of division 

 in the nucleus which have hitherto been overlooked or mistaken for its 

 dissolution. I strongly suspect that such is at least the case with 

 Strasburger's observations on the cell division of Isoetes. The excep- 

 tional cases with Ascomycetse point in the same direction. If such a 

 restriction of free cell-formation should be realized in plants, the differ- 

 ences in the secondary modifications of "cell division in plants and ani- 

 mals would not be so divergent as they at present appear. 



Strasburger takes occasion, in considering Auerbach's views of the 

 nature of the nucleus, to expand his own ideas. He practically distin- 

 guishes three sorts of " Kernsubstanz " : one is an active kind, which is 

 collected at the "poles," and is thereby divided into two antagonistic 

 portions ; another is repelled by these poles, and collects as a median 

 nuclear plate ; and a third kind, not repelled by the substance of the 

 poles serves, in the form of filaments, to join the latter with the median 

 plate. The maximum removal of the poles from the nuclear plate seems 

 to be soon attained ; but as the poles continue to repel each other, it re- 

 sults that the nuclear plate is thereby divided into halves. He concludes 

 that the nuclear plate plays a passive role, since a median portion of the 

 same is drawn out in the form of fine [interzonal] filaments. 



I do not fully agree with these conclusions. Strasburger himself 

 grants that the "nuclear poles "are "in stofflicher Beziehung von der 

 iibrigen Kernmasse verschieden," in that they are more highly refractive. 

 It is therefore an assumption when he says the " poles " consist of nuclear 

 substance. It is unsatisfatory to assume that the substance of the nu- 

 clear plate acquires its equatorial position in virtue of a repulsive influ- 

 ence exercised on it by the " poles," since it leaves unexplained how it 

 is that the same substance subsequently approaches these " poles." The 

 nuclear fibres are probably not exclusively nuclear substance, since it is 

 demonstrable that they in some cases arise outside the nucleus, and it 



