CYANOPHYCEM 193 



at the nodal points. These were termed " plasmatic microsomes,'* 

 and served as centres for the accumulation of reserve material 

 elaborated by the pigmented parts of the protoplast. In the 

 greater number of species that were investigated there was no 

 clear differentiation into central and peripheral region, but the 

 plasmatic microsomes in the centre of the cell accumulated meta- 

 chromatin, while those at the periphery accumulated cyanophycin. 

 This is best exemplified in Chroococcus turgidus. In Gleocapsa 

 many of the cells showed a deeply staining network in the central 

 region, somewhat simulating the spireme stage of normal mitosis. 

 Merismopedia elegans showed the presence of a definite central 

 body at the time of division. This, however, was not of the same 

 nature as the nucleus of the higher plants, but was apparently an 

 accumulation of chromatin or allied material at the nodal points 

 of a small and definite area in the centre of the cell. Chroococcus 

 macrococcus showed the highest type of central body. This 

 central body was definitely nuclear in nature, and the cell contents 

 could therefore be differentiated into nucleus and cytoplasm. 

 Only the peripheral portions of the central body stained with the 

 usual nuclear stains and showed a fine reticulum of chromatin at 

 the nodal points. There was a sap-vacuole in the interior of this 

 nucleus. According to Acton, the evolution of the so-called 

 nucleus in this group has taken place along the following, lines : 

 excess of food material elaborated by the pigment of the proto- 

 plast was first stored by the plasmatic microsomes as the carbo- 

 hydrate, cyanophycin. As, however, more and more material 

 was elaborated, the reserve in the centre of the cell became more 

 complex in nature and the protein metachromatin granules were 

 formed. In the course of time this accumulation of nucleo-protein 

 was restricted to a particular area in the cell, and at first this 

 restriction only occurred at division (Merismopedia). In this way 

 a portion of the cell came to be physiologically differentiated on 

 account of its function in connection with division. This area is 

 the nucleus. At a still later stage this incipient nucleus became 

 stabilised and was always present. C. macrococcus exhibits the most 

 primitive stage in the evolution of the Cyanophycean nucleus. The 

 central body here divides and there is no evidence of mitosis. It 



R.A.M. 7 



