Divisio7i in the Root of Vicia Fab a. 175 



substance — (this becoming the more evident during the aggre- 

 gation) — and not, according to my preparations, as Dr. Mont- 

 gomery states, merely wound around its surface. The 

 nucleolus is the centre around which the aggregation of 

 nuclear substance, which leads to the formation of the thread, 

 occurs. 



Nucleolar Divisioii. — This is a very common feature. The 

 rounded nucleolus (Fig. i) loses its form, becomes elongate 

 (Fig. 2), then dumb-bell shaped and finally a constriction 

 occurs and two equal nucleoli are to be seen (Fig. 3). 

 But the interesting feature lies in the fact that this nucleolar 

 division occurs and is often complete before the slightest trace 

 of any nuclear aggregation occurs, /. e., before any trace of a 

 nuclear division (Fig. 4). Frequently, nucleolar division 

 occurs during the aggregation. This can probably best be 

 explained by regarding the two nucleoli as centers, around 

 which aggregation occurs. There is apparently no regular- 

 ity as to the exact time for nucleolar division. 



The nuclear thread is now of a bluish crimson color. It is 

 a thin, long, almost continuous thread, irregularly wound 

 through the nucleus. It consists of linin material, with the 

 more deeply stained chromatin granules disposed at intervals 

 along its course. At one or at several points this thread can 

 be seen to dip into the nucleolus (Fig. 6). This is not to be 

 regarded either as an exceptional phenomenon or one difficult 

 to see. Every preparation of the bean root, which shows 

 division at all, shows many such figures (Figs. 7, 8, 9, 10). 

 This relation is retained as long as any trace of a nucleolus is 

 present. The nucleolus now begins to transfer its contents 

 into the nuclear thread. During the early formation of this 

 thread it seems to be in connection with the nucleolus at 

 many points. But as the smaller masses unite to form the 

 long, almost continuous thread, it is usual to see this thread 

 dip intc^the nucleolus at one point, though it is not uncom- 



