CHAPTER II 



CYANOPHYCEAE 



^INTRODUCTION 



This order used to be known as the Myxophyceae, but as this name 

 was originally applied to a very heterogeneous group of organisms 

 it is now customary to employ the name Cyanophyceae. The 

 members of the group are characterized by a bluish green colour 

 which varies greatly in shade, depending upon the relative pro- 

 portions of chlorophyll a, /^-carotin, myxoxanthin, phycocyanin and 

 sometimes xanthophyll and phycoerythrin. The internal structure 

 of the cell is extremely simple because a true nucleus and chromato- 

 phores are absent. Some authors have reported the presence of a 

 nucleus with rudimentary chromosomes which undergo a form of 

 mitosis, but these structures cannot be regarded as clearly esta- 

 blished. The protoplast possesses two regions, a peripheral one 

 containing the pigment together with oil drops and glycogen, and a 

 colourless central area which contains granules. Two kinds of 

 inclusions have been recognized. The metachromatic or a gran- 

 ules that lie in the colourless central area and which are nucleo- 

 proteic in nature since they give a Feulgen reaction. These granules 

 have probably been mistaken by some workers for chromosomes, 

 especially since it is found that they can divide by simple fission, 

 although some authorities do not consider that this is even a primi- 

 tive form of mitosis. The material of the central area is regarded by 

 such workers as equivalent to the cytoplasm in the cells of higher 

 plants. The other type of granule is known as the cyanophycin or 

 jS granule and occurs in the peripheral region. They are in the nature 

 of a protein reserve, and their presence is probably dependent to a 

 considerable extent upon the external environment. 



The protoplast is normally devoid of vacuoles, and this fact may 

 explain the great resistance of the plants to desiccation and of the 

 cells to plasmolysis. In some forms, principally species which are 

 planktonic, pseudo-vacuoles may be found, and it is supposed that 

 these contribute towards their buoyancy. The protoplast is sur- 

 rounded by an inner investment which has been shown to be a 



