404 BOTANICAL GAZETTE . [DECEMBER 
Preliminary to mitosis, the delicate network becomes some- 
what coarser and the thread somewhat broader, and gradually in 
many different parts the chromatin granules appear in irregular 
rows as chains of beads of different lengths. There are about 20 
of these chains, as illustrated in jigs. 2a—2c, which represent three 
sections of the same nucleus. They are the beginnings of the chromo- 
somes, similar to the prochromosomes described by Overton (58) 
in the presynaptic stage in the pollen mother cells of Thalictrum and 
three other species of flowering plants. The material which accumu- 
lates in these prochromosomes must come from the chromatin gran- 
ules imbedded in the linin thread, for it is evident that the nucleolus 
does not contribute any material directly to their formation. This 
behavior is therefore similar to the process of chromosome formation 
in higher plants, and is very different from the condition reported by 
Wo tre (86) for Nemalion, where the chromosomes are described as 
coming out from the nucleolus. The nucleolus of Polysiphonia 
remains unchanged while the prochromosomes are being formed. 
These prochromosomes gradually become more pronounced, increase 
in breadth, and the bead-like structure is transformed into the more 
homogeneous rod-shaped chromosomes that become distributed 
through the whole nuclear cavity attached to a linin thread, as shown 
in figs. 3a and 3b, which represent two sections of the same nucleus. 
The nucleolus may remain undivided or fragment into two at this time. 
The cytoplasm around the resting nuclear membrane appears at 
first homogeneous, but during prophase there is a gradual accumu- 
lation on the two opposite sides of the nucleus, and finally two deeply 
staining centrosome-like bodies appear, forming the poles of the more 
slightly elongated nucleus (fig. 4). While these changes in the cyto- 
plasm are going on without the nucleus, some important events take 
place within. The chromosomes become thickened and more com- 
pact and gather in the middle region of the nuclear cavity, with linin 
threads still attached to their ends, and at last they are arranged in 
the equatorial plate (fig. 5). The nuclear membrane is still present 
when the spindle is developed (jig. 5), so that the latter is conse- 
quently intranuclear. 
It is very interesting to compare this stage with the previous one 
(fig. 4), taking into consideration the kinoplasmic centers, the shape 
