254 University of California Publications. [Botany 



marily upon the nucleus of Tolypothrix lanata, but he says on 

 p. 177 : ' ' Der Verlauf der mitotischen Kernteilung ist nun genau 

 derselbe bei den beiden scillatoria- Arten wie bei Tolypothrix." 



Zacharias, who has done much work on the cytology of the 

 Cyanophyceae, states that through the kindness of Dr. Kohl he 

 has been permitted to examine these preparations, and after do- 

 ing so, fails to agree with his conclusions. He remarks concern- 

 ing these preparations that "Die starker gefarbten, mannigfach 

 gestalteten Teile der Zentralkorper, wie sie die Praparate und die 

 Figuren der Autoren zeigen, halte ich nicht fur chromosomen, 

 sondern fur (teilweise auch durch das Praparations-verfahren 

 deformierte) Vorspriinge, Leisten, etc., der Zentralkorper." 



Judging from preparations treated in like manner, I agree 

 with Zacharias that these projections, etc., are not chromosomes 

 as ordinarily understood. 



Phillips has a more complicated scheme for mitosis than Kohl. 

 In fact, he has two methods, both of which he says may occur in 

 thp same species. It would be exceedingly interesting to learn 

 under what condition these two processes take place, and why one 

 should occur at one time, and another at another time. 



In either case, the resting condition of the cell is described as 

 having the chromatin distributed within the nucleus in the form 

 of hollow vesicles, and, when nuclear division begins, the first 

 .step is the transformation of these chromatin vesicles into a dif- 

 fuse mass throughout the nucleus. This diffuse mass now collects 

 into a network of threads along which, particularly at the junc- 

 tion of the threads, are arranged chromatin granules, which in- 

 crease in number by division in a plane perpendicular to the 

 thread. At this stage one of two things may happen. The net- 

 work is either constricted in the middle into two parts after being 

 drawn to the "equator of the cell," or it is resolved into a spi- 

 reme thread. If the former case prevails, the two masses are 

 drawn into the daughter cells and separated from each other by 

 the ingrowing cross-wall. Of their subsequent history nothing is 

 said. 



If the other process prevails, after the orientation of the spi- 

 reme in the direction of the long axis of the cell, it breaks up into 

 a number of "segments" or "chromosomes." At this juncture 



