378 BULLETIN OF THE 



increase in number and volume, and are employed for the construc- 

 tion of the cell plate. Their exact signification in the formation of 

 the " Hautschichtplatten " may not warrant his earlier (first edition) 

 conclusions as to the identity of nuclear substance and. " Hautschicht." 

 He is now inclined to believe that there is simply an accumulation 

 of " Hautschichtmasse " between the Kernfaden, especially since the 

 Hautschichtplatte is formed in some places without the assistance of 

 these filaments; the real signification of the latter may, perhaps, sim- 

 ply be to guide the substance necessary for the formation of the plate 

 in the proper courses, and possibly to afford (mechanical 1) support to 

 the plate. From the manner in which the Hautschicht is preformed 

 along the future plane of division in plant cells it is certain that it can- 

 not be compared to the denser layer produced at the surface of liquids 

 by superficial tension. He also thinks the " Einschniirungstheorie " is 

 disproved by this observation. 



Strasburger can hardly be justified in extending the latter conclusion 

 to animal cells, especially since there is clear evidence of an infolding of 

 peripheral substance in cases (e. g. Rana) where pigment, at first limited 

 to the superficial portions of the cell, follows the deepening constriction. 



The splitting of the cell plate ensues certainly under the influence of 

 the two nuclei, perhaps from reasons similar to those which cause a 

 splitting in the nuclear plate. 



Although he claims for the nucleus a controlling influence in the 

 process of cell division, he is compelled to admit in certain cases (spores of 

 Anthoceros, macrospores of Isoetes, etc., where the old nucleus is " pushed 

 to one side and finally dissolved," while the function of division is as- 

 sumed by an " Attractionsmasse " which is individualized near by) that 

 the nucleus has lost its power of division. The explanation given is 

 that new nuclear substance has been collected about the old nucleus, and 

 has assumed the function of the latter.* The necessary phyllogenetic 

 connection of this with the more typical division is at once demonstrated 

 by the fact that the nearest relatives of these plants (indeed, the micro- 

 spores of the same Isoetes plant) exhibit the normal method of cell 

 division in their spores. 



I have no objection to considering, with Strasburger, this modified 

 form of division as the result of independent adaptations (induced, per- 

 haps, by the same causes) in each of the cases which he cites ; but I 

 cannot consider the process so fundamentally different from the typical 



* ** In der That sahen wir diese am Kern angesammelte Masse mitihren Starkeein- 

 schliissen sich ahnUch wie sonst die Substanz der Kerne bei der Theilung verhalten." 



