MORPHOLOGY 



79 



also noticed that the frequent yellow coloration of phytomonads in 

 moorland pools is due to a development of carotin in the chro- 

 matophores as a result of deficiency in nitrogen. Johnson (1939) 

 noted that the haematochrome granules of Euglena rubra become 

 collected in the central portion instead of being scattered through- 

 out the body when sunlight becomes weaker. Thus this Euglena 

 appears green in a weak light and red in a strong light. 



Flagella 



Stigma 

 Pyrenoids 



Chromotophores 



— Nucleus — 



Shell 



Chromatophores 



Pyrenoids 



Fig. 31. a, Trachelomonas hispida, X530 (Doflein); b, c, living and 

 stained reproductive cells of Pleodorina illinoisensis, XlOOO (Merton); 

 d-f, terminal cells of Hydrurus foetidus, showing division of chromato- 

 phore and pyrenoid (Geitler); g-i, Chlavujdomonas sp., showing the di- 

 vision of pyrenoid (Geitler). 



In association with the chromatophores are found the pyrenoids 

 (Fig. 31) which are usually embedded in them. The pyrenoid is a 

 viscous structureless mass of protein (Czurda), and may or may not 

 be covered by tightly fitting starch-envelope, composed of several 

 pieces or grains which appear to grow by apposition of new material 

 on the external surface. A pyrenoid divides when it reaches a certain 

 size, and also at the time of the division of the organism in which it 

 occurs. As to its function, it is generally agreed that the pyrenoid is 

 concerned with the formation of the starch and allied anabolic prod- 

 ucts of photosynthesis. 



