ADDENDA 



SINCE the foregoing pages were printed off a number of papers have 

 appeared to which it is desirable to make some reference. 



In the Myxophycese the cytology of the Chroococcaceae has been very 

 carefully studied by Miss Acton (Ann. Hot. xxviii, 1914) who states that 

 ' there is a gradual transition in the structure of the cell from an almost 

 undifferentiated condition in the lower types to a somewhat specialized one, 

 of which Chroococcus macrococcus represents the highest type examined, and 

 Merismopedia elegans an intermediate stage.' In Chroococcus macrococcus 

 there is a definite incipient nucleus and cytoplasm. Miss Acton suggests 

 that the evolution of the 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 protein metachrornatin 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 physiologically and morphologically 

 separated on account of its function in connection with division.' This 

 area is called by the present author the 'incipient nucleus' (consult p. 7). 

 Miss Acton goes on to state that ' at a later stage the " nucleus " became 

 stable and was always present, as in Chroococcus macrococcus.' 



The cytology of Glaucocystis Nostochinearum has been investigated by 

 Griffiths (Ann. But. xxix, 1915) who states that ' Glaucocystis is probably 

 a member of the Cyanophycea? owing to the presence of an " open " nucleus 

 at one stage ; the tendency of cytoplasmic division to take place independently 

 of nuclear division ; and to the presence of phycocyanin in the chromoplast. 

 The very high differentiation of the nucleus in the dividing stage ; the 

 elaborate chromoplast to which the phycocyanin is confined ; the formation 

 of daughter-cells very similar to those of Oocystis ; and the cellulose character 

 of the cell-wall, are features which separate Glaucocystis from all the rest of 



