Chapter X 



MYXOPHYCOPHYTA 

 MYXOPHYCEAE 



* Introduction 



This class has also been known as the Cyanophyceae, but of recent 

 years Myxophyceae has become more generally adopted. The 

 separate plants, which individually are all microscopic, are 

 characterized by a bluish-green colour which varies greatly in 

 shade, depending upon the relative proportions of chlorophyll a, 

 ^-carotene, myxoxanthin, myxoxanthophyll, phycocyanin and 

 phycoerythrin. The internal structure of the cell is extremely simple 

 because true nucleus and chromatophores are absent. The proto- 

 plast possesses two regions, a peripheral one containing the pig- 

 ment, together with oil drops and myxophycean starch (or glycogen), 

 and a colourless central area that contains granules. Two kinds of 

 inclusions have been recognized. The first are the metachromatic 

 or a granules that He in the colourless central area : these are nucleo- 

 proteic in nature since they give a feulgen reaction. Whilst many 

 consist of metachromatin, the feulgen reaction indicates that true 

 chromatin is also present. In the past they have probably been 

 mistaken by some workers for chromosomes, especially since it is 

 found that they can divide by simple fission, though this does not 

 necessarily indicate a primitive form of mitosis. The other type of 

 granule is known as the cyanophycin or /8 -granule and occurs in 

 the peripheral region. They are in the nature of a protein reserve, 

 and their presence is dependent to a considerable extent upon the 

 external environment. 



The protoplast is normally devoid of vacuoles, except in old 

 moribund cells, and this is a major factor contributing to 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 by virtue of the gas that they are said to 

 contain. The protoplast is surrounded by an inner investment, 



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