436 Acton,— Observations on the Cytology of the Chroococcaceae. 
would seem to correspond to that of the chromatin in the more advanced of 
Gardner’s diffuse type ; but Guilliermond describes this reticulum as con- 
sisting of an achromatic ground substance containing granules of chromatin. 
He thinks that it ought to be considered as a true chromatic network, and 
compares it with the ‘ appareil chromidial ’ described by zoologists in 
certain Protozoa. Division is amitotic. There is no spireme nor chromo- 
somes, neither do the chromatin granules divide. The only suggestion 
of mitosis is that in some more highly developed species the threads of the 
network tend to become drawn out in parallel lines, though the anastomoses 
do not disappear and the reticulum is not broken. 
The cortical layer does not constitute a true chromatophore, but 
contains the pigment in a state of solution. In the central body he 
observes {a) ‘corpuscules metachromatiques ’ (Kohl’s central granules); 
(b) ‘ corps nucleoliformes ’ of A. Meyer ; and in the cortical cytoplasm 
cyanophycin granules. 
Swellengrebel (’10), who has investigated only one species, Calothrix 
fusca , describes a central body consisting of an alveolar achromatic ground 
substance in which are embedded granules and filaments of chromatin. 
There is no very marked distinction between the groundwork of the central 
body and the surrounding cytoplasm, and sometimes the chromatin is 
diffused throughout the whole cell, so that the distinction between central 
body and cytoplasm seems to be lost. Division is amitotic. 
Brown (’ll) in a species of Lyngbya finds a nucleus which, in the 
stages between division, resembles the resting nucleus of higher plants, except 
for the absence of a limiting membrane. It contains a mesh of fine fibres, 
along which small granules are scattered ; the fibres are embedded in 
a clear substance resembling nuclear sap. 
Dobell (T2) in a paper on Spirochsetes briefly mentions three species of 
Blue-green Algae, and states that there is a definite central body in these 
species. 
It will be seen from the foregoing account that, with the exception of 
Fischer, all investigators since 1902 conclude that there is a definite nucleus. 
Since, however, none of them agree on the details of its structure even when 
examining the same species, the value of these conclusions seems somewhat 
questionable. The evidence in support of the theory of a nucleus which 
divides mitotically is certainly inconclusive. With regard to the structure 
of a nucleus which divides amitotically there seems to be more agreement. 
Judgingfrom figures, the achromatic ground substance of Guilliermond and 
the chromatin of Gardner occupy similar positions in the cell. Both stain 
more deeply than the surrounding cytoplasm, yet Guilliermond believes 
the substance to be achromatic, while Gardner thinks it is chromatin. As 
stated before, it is difficult to believe that there is as much chromatin 
present as Gardner describes. 
