Acton. — Observations on the Cytology of the Chroococcaceae. 449 
masked iron and organic phosphorus, and are therefore nuclein compounds, 
but states that they are not true chromatin. 
Fischer denies the nuclein nature of these granules, and says they 
are simply accumulations of a carbohydrate reserve to which he gives 
the name { anabaenin \ It is quite possible that in some forms, and at 
certain times in other species, the granules in the central region are entirely 
carbohydrate in composition. The plasmatic microsomes served probably 
first of all as centres for the accumulation of the excess of food-material 
elaborated by the pigment in the peripheral region. This would naturally 
be in the first place of a carbohydrate nature. But as evolution proceeded 
we might expect that the central region would become a centre for further 
metabolic activity, and so gradually nuclein compounds would be found as 
reserve, and finally true chromatin would be evolved. It would be some- 
where about this stage that such a form as Chroococcus targidus arose. 
A few of the plasmatic microsomes in the central region may consist of true 
chromatin, but this has not been definitely proved. 
The difference in staining capacity shown by various parts of the 
ground substance at certain times has still to be considered. These deeply 
staining areas correspond in arrangement sometimes to the chromatin 
shown by Gardner (’ 06 ) in his Figs. 4, 5, 9, but the arrangement is not 
constant ; it varies from numerous small areas to one or two large ones, 
as though the smaller areas gradually merged into each other. They 
do. not stain nearly as intensely as chromatin should, and they are not 
a constant feature, so that there is no reason to regard them as nuclear 
structures. 
It would appear that when the accumulation of reserve material 
reaches its maximum the central granules begin to diffuse into the ground 
substance. A similar diffusion of the central granules into the ground 
substance has been mentioned by Gardner, 1 and diffusion of both volutin 
and chromatin into the cytoplasm has been described by Wager and 
Peniston 2 in the Yeast-plant. 
The majority of the cells showing this diffusion are in a state of active 
division, and so the dissolved material would gradually be utilized in 
growth. Then, possibly, a resting period occurs in which nuclein material is 
again stored up in the central granules. When this accumulation reaches 
its maximum, active division again sets in, and so eventually the formation 
1 These granules (a granules) disappear before the spore reaches maturity. 1 They do not 
disappear at once, but become gradually smaller and finally disappear entirely.’ The a granules 
probably give up their material either to form chromatin or to form the /3 granules, and the former 
is more likely, since they are so closely united to the chromatin. 
2 ‘ It is possible that in the yeast-cell there is a constant interchange of chromatin between 
nucleus and cytoplasm.’ Speaking of volutin granules, he states : * there can be no doubt that they 
become dissolved in the cytoplasm, which becomes intensely stained with methylene blue just at this 
stage.’ 
