99 6 Gates . — Somatic Mitoses in Oenothera. 
progressively thicker and more conspicuous. This is accompanied in some 
threads by an intensification of the moniliform character, while other por- 
tions of the threadwork become thicker and quite homogeneous in appear- 
ance (Fig. 3), having a rather loose texture and presumably formed by the 
fusion of several threads. This is, frequently at least, accompanied by 
a movement of material towards the periphery of the nucleus, for the 
thicker threads are usually more conspicuous in this region. They are also 
more strongly moniliform, thus giving the periphery of the nucleus a more 
densely chromatic appearance. 
At a slightly later stage than that of the last figure the chromosomes 
begin to be sufficiently definite so that they can be counted approximately. 
There is some variation at this time in the manner of their first appearance 
as definite chromosome bodies. Sometimes they first appear as very long 
and narrow, deep-staining, twisted threads in the nucleus (Fig. 4). In this 
figure only a portion of the chromosomes are drawn, in order to show the 
complete outlines of certain ones. In other cases the bodies which are 
destined to become chromosomes are shorter and thicker, and much less 
twisted when they can first be observed (Figs. 3, 5, and 6). 
The formation of the body of the chromosome seems, therefore, to 
be the result of progressive parallel fusion of numbers of strands in the 
original reticulum. The threadwork is thus swept up into a few thick 
strands which from the first show a marked tendency to occupy the periphery 
of the nucleus. The finer threads visible in Figs. 5 and 6 finally all dis- 
appear, presumably by absorption into the denser masses, and the chromo- 
somes meanwhile continue to shorten and thicken progressively. In Fig. 7 
this process has proceeded farther than in Figs. 5 and 6, and the chromosome 
number can now be definitely counted — 15. 
During these processes the nucleoli remain unchanged, floating freely 
in the nuclear cavity until the nuclear membrane disappears, when they are 
suddenly dissolved and vanish. 
It will be seen from the preceding figures that nothing even remotely 
resembling prochromosomes is to be found in the resting nucleus* I have 
sought for these bodies, using a Variety of depths of stains, and am convinced 
there are no such bodies present in the resting nucleus. The nucleoli and 
the bead-like thickenings of the threads of the nuclear reticulum are 
the only dense bodies to be observed. The latter are very numerous, and, 
as can be seen from Figs. 1-3, a number of them occur along any length of 
thread equal to that of the chromosome. I can only conclude that there is 
no evidence whatever for the persistence of denser chromosome centres or 
prochromosomes in the completely resting nuclei of these cells. The 
passage into a moniliform threadwork or reticulum is complete, no denser 
aggregations except the easily recognizable nucleoli, which are usually only 
3 or 4 in number, remaining in any part of the nucleus. 
