460 Smith.—Cyiological Studies in the Protococcales. Ill, 
nucleole and nuclear membrane, while the chromatin is indistinct. As the 
cell grows there is an increase in the size of the nucleus, the chromatin 
granules becoming more distinct but never standing out sharply in the 
resting nucleus. In favourable preparations faint linin threads may be 
seen connecting the chromatin granules. 
I have been able to follow the details of nuclear division more fully in 
this alga than in any other member of the Protococcales that I have studied. 
The first indication of nuclear division is a decided increase in the size of 
the nucleus, while certain f granules’ become very prominent. This may be 
seen by comparing PI. XV, Figs. 7 and 8, or 22 and 23. The proper inter¬ 
pretation of these ‘ granules ’ is a matter of doubt. A fairly definite spireme 
thread may be seen in the nuclei of certain cells (Fig. 9). These ‘ granules ’ 
may be chromosomes that have been derived by a segmentation of this 
spireme, or they may be chromatin granules which have become more 
distinct. In dealing with such small nuclei there is great danger of forcing 
an interpretation based upon our general knowledge of the process of 
karyokinesis in other plants; so that it is better to leave the nature and 
origin of these nuclear ‘ granules ’ an open question. In the equatorial plate 
stage the spindle is distinctly bipolar, the two ends gradually tapering from 
the mass of chromosomes on the equatorial plate. Little can be said con¬ 
cerning its origin, although the hyaline area surrounding the spindle in 
Fig. 10 suggests that it is of intranuclear origin. In some preparations 
there are prominent granules at the poles of the spindle, but no polar radia¬ 
tions (Fig. 33). These polar granules were only noted during the meta¬ 
phases. The chromosomes are densely aggregated on the equatorial plate 
and can only be studied in a polar view of the spindle, when about eight can 
be seen (Figs. 24, 32). The chromosomes move from the equatorial plate 
in a dense mass (Fig. 20), and remain bunched after they reach the poles 
(Fig. 16). Details are lacking concerning the reconstruction of the daughter 
nuclei. 
The cytoplasm of the young cells is densely granular. Occasionally 
there are vacuoles in growing (Fig. 2), or mature cells (Fig. 8), but this is 
the exception rather than the rule. Lagerheim ( 1 ) has shown that there 
is a definite parietal chloroplast in T. minimum . This stands out quite 
sharply in living cells, but is difficult to observe in stained preparations. 
The chloroplast is denser than the rest of the cytoplasm (Fig. 7), which is 
sometimes very finely reticulated. 
Pyrenoids, about the size of the nucleole, are present in the youngest 
cells. The triple stain is best for differentiating their presence, since the 
pyrenoid always stains a bright red. I have found that more than one of 
these organs in the cells of Characium ( 5 ) and Pediastrum (6) is not 
uncommon, whereas in Tetradesmus ( 3 ) and Scenedesmus ( 4 ) it is very rare. 
In this respect Te true dr on resembles Tetradesmus and Scenedesmus, since not 
