448 Acton. — Observations on the Cytology of the Chroococcaceae 
It is also possible that Chr. macrococats is identical with a Chroothece 
described by Hansgirg (’84). Hansgirg’s description of Chroothece Richteria- 
num is in exact agreement with the characters of Chr. macrococcus , except 
as regards colour. He finds in the cell an orange-coloured, rarely blue-green 
‘ chromatophore ’ with ray-like processes spreading into the periphery of 
the cytoplasm. The apparent star-shaped orange 4 chromatophore ’ can 
often be seen in Chr. macrococcus , but it has never been described as blue- 
green. He finds in the older cells of Chroothece a one-sided development of 
the cell-wall on damp earth, but not in the younger cells, nor in the water 
forms. As the colour of Chr. macrococcus is very variable, it seems not 
unlikely that the two species are the same. 
VII. Summary. 
It is not surprising that in many of the Chroococcaceae there should be 
no nucleus, not even a primitive one. In the course of evolution there must 
have been a stage in which there was no nucleus, or in which the cell was all 
nucleus, depending upon the point of view, and we should expect to find this 
condition in some of the more primitive unicells. The Cyanophyceae are 
undoubtedly a very primitive and ancient group, and it is not unlikely that 
some of the early stages in the evolution of the nucleus may be shown 
in these plants. The type represented by Chroococeus turgidus may 
be a very early stage, in which the difference in function between the inner 
and outer region of the cell has not yet produced any morphological 
differentiation. 
There is in this species a protoplast consisting of a matrix or ground 
substance traversed by a reticulum of delicate threads, and at the junctions 
of these threads small granular thickenings occur. There is no difference 
in the size of the mesh of the reticulum in any part of the cell. Thus there 
is no differentiation in form. But there is a difference in composition. In 
the portion immediately beneath the cell-wall the plasmatic microsomes 
do not stain deeply with any stains except cytoplasmic ones, and seem to be 
of the same nature as the reticulum. Further inwards, the plasmatic micro- 
somes appear to contain accumulations of material, and stain deeply with 
brilliant blue, and in the central region the microsomes contain accumula- 
tions of metachromatin, which, although it is not true chromatin, is 
undoubtedly allied to it. The close connexion between the metachromatin 
granules and chromatin has probably been the cause of much confusion 
in the earlier papers on the Cyanophyceae. They react with most chromatin 
stains, though not all, 1 and Macallum (’99) has shown that they contain 
1 Iodine-green-fuchsin, which invariably stains the nuclei intensely blue and the cytoplasm red 
in other forms which may be found on the same slide, such as Desmids and Frotozoa, never seems 
to give more than a purplish tint to the central granules. 
