452 Ac ton. — Observations on the Cytology of the Chroococcaceae . 
probably a sap vacuole. The cytoplasm is simply the ground substance of 
the former types broken up by cell-sap vacuoles, which give it a coarsely 
reticulate appearance. The fine reticulum is present but is very much 
distorted, except in the neighbourhood of the ‘nucleus’. The plasmatic 
microsomes are very small and indistinct. 
12. It is suggested that evolution of nucleus and cytoplasm has taken 
place along the following lines : The excess of food-material elaborated by 
the pigment was first stored in the plasmatic microsomes as a carbohydrate — 
cyanophycin. As more and more material was elaborated, the reserve 
in the central region became more complex, and the proteid metachromatin 
granules were formed. In time, the accumulation of nucleo-protein became 
restricted to a very limited area in the cell, so as to ensure its equal 
distribution on division, and this restriction only occurred on division, 
as in Merismopedia elegans . In this way, part of the cell became physio- 
logically and morphologically separated on account of its function in con- 
nexion with division. This area may be called the ‘ nucleus ’. At a later 
stage the ‘ nucleus ’ became stable and was always present, as in Chroococcus 
macrococcus. The ground substance also altered in character, forming 
a definite cytoplasm as described above. 
In conclusion, I wish to express my thanks to Prof. G. S. West 
for suggesting the investigation, for continual help and encouragement in 
the work, and for providing the greater part of the material examined. 
Botanical Laboratory, 
University of Birmingham. 
Literature cited. 
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F rscHER, A. (’05) : Die Zelle der Cyanophyceen. Botan. Zeitung, Bd. Ixiii, 1905, p. 51. 
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Hansgirg, A. (’88) : Ueber Bacillus muralis , Tomaschek, nebst Beitragen zur Kenntniss der 
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Hassall, A. H. (’ 45 ) : British Freshwater Algae. I, 1845, p. 324. 
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