Graham . — Nuclear Division of Preissia commutata . 675 
The spindle lies in a space almost free from cytoplasm, plastids, &c. The 
poles of the spindle are broad and blunt, though there may be a multipolar 
diarch (Fig. 14). 
As the chromosomes draw towards the poles (Figs. 14, 16) some are 
often in advance of the others. At this stage the chromosomes are plainly 
two-pointed (Fig. 17), a condition described and figured by Overton (’ 09 ) 
and others. As the chromosomes reach the poles (Fig. 18) they are 
grouped together, but do not, at least at the early telophase, lose their 
individual outline. In cross-section the cell plate appears as a line across 
the equator of the spindle at the time the chromosomes have reached the 
poles (Fig. 18). 
The reconstruction of the daughter nuclei of the heterotypic division 
takes place very quickly. The wall separating the two daughter nuclei of 
the first division is scarcely formed, when they begin to show signs of early 
prophase preparatory to the formation of the four spores. No sections 
showing the steps between the grouped chromosomes at telophase and 
a daughter nucleus with a reticular content, a nucleolus, and a nuclear 
membrane (Fig. 19) were found. The reconstruction of the daughter nuclei 
is evidently passed over very quickly. After a short time the nuclei enlarge 
(Figs. 20, 21) and the chromatin strands thicken. The nucleolus also 
enlarges and chromatin bodies appear (Figs. 20, 21). 
In the second mitosis of the spore mother-cell the daughter nuclei 
divide simultaneously. In Fig. 23 three newly formed nuclei are repre- 
sented ; the other one and the first wall laid down in the spore mother-cell 
are in another section. 
Spindle fibres, so difficult to obtain in the first division of the spore 
mother-cell, are most conspicuous in the early prophase of the daughter 
nuclei. Whether they are preceded by a cap of hyaline cytoplasm, as is 
the case in the somatic cells of Preissia , was not determined. At the 
earliest prophases of the spore mother nuclei in the heterotypic division 
hyaline caps are closely applied to the nuclear membrane (Figs. 22, 24, 25). 
In an effort to understand the origin and function of these caps, sections were 
cut 5 [jl thick. This is too thin a section to study the nuclear phenomena, 
but Figs. 22 and 24 are probably both in the reticulum stage. The form of 
the hyaline cap varies, as a comparison of Figs. 22 and 25 shows. Their 
position against the nuclear membrane also varies ; they may lie on opposite 
sides of the nucleus, or there may be a greater distance between them on 
one side of the nucleus than on the other side (Fig. 22). Coarse strands of 
cytoplasm may extend over the hyaline caps from a group of plastids to 
the nuclear membrane. Whether the outer spindle fibres are developed 
from these hyaline caps, as is the case in the somatic cells, or whether the 
spindle fibres are developed from a zone of fibres circling about the nucleus, 
as is the case in Seed Plants, the present investigation does not prove. 
