Acton. — Observations on the Cytology of the Chroococcaceae. 441 
the plasmatic microsomes in the central region have the characteristic 
reactions of metachromatin. They stain deeply with haematoxylin, Loeffler’s 
methylene blue, &c., and take on a reddish blue tint with iodine-green- 
fuchsin. 
The latter stain does not appear to differentiate very clearly the various 
granules in the cell. Even the large metachromatin granules can often only 
be recognized because they are refractive. 
Kohl (’03) states that the metachromatin granules are not stained with 
this combination, and that chromatin should stain green blue to blue violet. 
I find that metachromatin is often uncoloured, but at times gives the colour 
reactions which Kohl ascribes to chromatin. In Fig. 6 the dark granules 
stained a distinct green blue, yet they correspond in size and number to the 
metachromatin granules in other cells of this collection. Many of them 
contained very little metachromatin. At the same time the author does 
not deny the possibility of these granules being true chromatin, especially 
considering the position of the chromatin in those forms which have a distinct 
central body. 
The large irregular, apparently hollow, metachromatin granules were 
found to be simply large accumulations of metachromatin, or, perhaps more 
correctly, clusters of metachromatin granules filling up a whole mesh of the 
network (Fig. 2 ). The granules are very refractive and thus give a dark 
edge on focusing, causing the appearance of a darkly stained rim (Fig. 2 ). 
Possibly these correspond to the hollow granules of Kohl and others. 
It is possible that these clusters of granules, taken in conjunction with 
the imperfectly observed network, may have given rise to the statement of 
Phillips (’04) that ‘ The chromatin is aggregated in hollow vesicles in the 
resting cell. These vesicles give out chromatin to the net spireme very 
much like the nucleolus of the higher plants, and they may represent it.’ 
He also describes on division a network of threads connecting chromatin 
granules. It will be shown that the metachromatin does actually diffuse 
into the ground substance. 
It has been stated before that the number of metachromatin granules 
in the central region varies with the condition of the material. When the 
number is large, the groundwork seems to stain equally in all parts, but if 
the number of deeply staining granules is comparatively few, the ground 
substance differs in parts in its capacity for staining. This is especially 
well shown in slides stained with methylene blue. Certain parts of the 
ground substance stain more deeply than the rest, but they do not stain 
nearly as deeply as the metachromatin granules. Plasmatic microsomes, 
faintly stained like the remainder of the ground substance, can be seen in 
the central region. 
These deeply staining areas are generally circular or elliptical in shape, 
and sometimes appear to be surrounded by a colourless rim. There may be 
