10 



Myxophyceae 



the nuclear functions are localized. The mere fact that division of the 

 protoplast may begin by the ingrowth of a ring-shaped septum before 

 there is any indication of division in the primitive nucleus seems to show 

 that that structure has not yet acquired all the physiological attributes 

 of a true cell-nucleus. 



THE PIGMENTS AND THE CYTOPLASM. In the majority of the Myxo- 

 phyceae the cells are of a rich blue-green colour, the pigments being located 

 in the peripheral zone of the protoplast which surrounds the incipient 

 nucleus. There are three pigments of importance, viz. phycocyanin, 

 chlorophyll, and carotin, of which the first is generally the most abundant 

 and to a great extent masks the chlorophyll. It is the combined effect 

 of the phycocyanin and chlorophyll which gives the characteristic 'blue-green' 

 colouration to the cells. Some forms are reddish-pink in colour and others 

 violet ; the former colouration is due to the predominance of carotin, and the 

 latter to the predominance of both phycocyanin and carotin over the 



Fig. 8. Synechocystis aquatilis Sauvageau, showing various stages of cell-division. 

 Very highly magnified (after Gardner). 



chlorophyll. One form of carotin has been named polycystin by Zopf; 

 and another form, which is identical with Sorby's pink phycocyanin, has been 

 named myxophycin by Choclat. All these pigments can be extracted by 

 appropriate methods (consult Lemmermann, '07, p. 9). The phycocyanin 

 is soluble in water, and after rapidly killing the cells, may be easily obtained 

 as a brilliant blue solution from which it can be crystallized. 



It has long been known that the Myxophycese occurring in deep water 

 are for the most part tinted red, and Gaidukov ('04 '06) has suggested 

 that this is a complementary chromatic adaptation due to the fact that 

 the quality of the light is affected by the depth of the water through which 

 the sun's rays have to pass. He found that a species of Oscillutoria changed 

 its colour when grown behind coloured glass or coloured solutions, and that 

 the change was always in the direction of taking on the colour comple- 

 mentary to the light in which it was placed. This complementary colour was 

 only assumed after a series of colour changes, and when once acquired 

 was retained for months after the Alga had been restored to white light. 



