ELEMENTS OF MICROBIAL CYTOLOGY 



21 



the lower forms, no mitochrondria seem to exist, but the chloroplastids 

 take on certain special characteristics. Instead of small scattered 

 corpuscles is found one, or occasionally several, large chloroplastids 

 filling most of the cell. They are in various shapes ribbons, spirals, 

 nets, etoilated bodies (Fig. 12), etc. but all appear to be made up of 

 a mitochondrial substance. Their physiological role is much more 

 general than in the chloroplastids of higher plants. They produce 

 not only the chlorophyl, but other pigment bodies, the starch or para- 

 mylum, metachromatic corpuscles, and globules of fat. Conse- 



I 



S^J 



FIG. ii. FIG. 12. 



FIG. ii. A cell from the root of a bean in which the rod-mitochondria (ch) 

 form in the course of their development amyloplasts from which (p) spring grains 

 of starch (a). 



FIG. 12. A, Euglena viridis with its star-like chloroplasts (chl.) at the center 

 of the organism, the pyr6noid body (Py) surrounded by grains of paramylum (Par), 

 eye-spot (0), contractile vacuole (v), flagellum (/), nucleus (n). (After Dangeard.) 

 B, Microglena punctifera, with two elongated chromatophores arranged longitudinally. 

 (After Stein.) 



quently the complex chloroplastids of the algae with their general 

 function have been considered as a special form of chondrium which, 

 instead of being scattered in the cytoplasm as a number of small 

 structures, finds itself gathered in very compact masses. 



The Cyanophycea are the only microorganisms in which the chon- 

 drium has not been found. In the Cyanophycea the chlorophyl and the 

 blue pigment (phycocyanin) associated with it are diffused throughout 

 the cytoplasmic area surrounding the nucleus. The very primitive 

 structure of the algae explains to some extent this absence of an im- 

 portant structure of the cell. 



