Carter . — The Cytology of the CladopJioraceae. 4 . 75 . 
the vacuoles diminishing as the chloroplast becomes more and more 
distended (Text-fig. i,a). 
In Ctadophora it is quite certain that these starch-grains which accumu- 
late in the chloroplast had their origin in the pyrenoids, as explained by 
Timberlake ( 1901 ), since they correspond fairly well with the starch-grains 
of the starch-sheaths in size and shape, and are often seen grouped in circles 
round the pyrenoids, having just been thrown off. In Rhizoclonimn , however, 
this is not quite so clear, for most of the grains lying free in the chloroplast 
are somewhat smaller in size than the large and peculiar grains which make 
up the sheaths of the pyrenoids. 
Division of the Nucleus. 
Division of the nucleus was observed in Ctadophora gtornerata , var. 
simplicior , Kiitz., and also in Rhizoclonimn hieroglyphicum , and was found to 
be very similar in both species. The resting nucleus is a more or less 
spherical body with one or more deeply staining karyosomes (Figs. 9, 23, 
and 24). 
In the particular form of Ctadophora examined the nucleoli were often 
particularly numerous, as many as three to five being present in some of the 
nuclei (Figs. 24 and 25). The nuclear reticulum contains practically no 
chromatin. 
The beginning of division is marked by the gradual disappearance of 
the nucleoli, the chromatin becoming dispersed through the whole nucleus* 
finally becoming associated into a spireme which in both species is very 
long, thin, and convoluted (Figs. 10-12 and 25-28). The contraction of 
the spireme was particularly clear in the case of Rhizoclonimn (Figs. 12-14). 
The shortened and thickened spireme was later observed to have split 
into a number of chromosomes which arranged themselves on an equatorial 
plate (Figs. 15, 29, and 30). The chromosomes are in both cases rod-like 
structures and are so numerous that it is almost impossible to count 
them. Division of the chromosomes evidently takes place whilst they are 
on the equatorial plate, for in the next stage two still very large groups of 
chromosomes are seen being pulled to opposite poles by the fibres of the 
nuclear spindle (Figs. 16-18 and 31). 
The telophase of the division is characterized by the gradual separation 
by constriction of the daughter nuclei. This is accomplished by the con- 
traction of the spindle in the region of the equator, some of the fibres being 
still visible for some considerable time (Figs. 18-20 and 32-34). 
Thus the daughter nuclei remain connected by a bundle of fibres which 
gradually diminishes in thickness and finally disappears altogether, leaving 
the two nuclei quite isolated (Figs. 21 and 35). 
Meanwhile, within the daughter nuclei themselves the chromosomes 
lose their identity and the chromatin rearranges itself, forming first a rather 
