366 



Conjugate 



etc., there may be many pyrenoids in' each chloroplast 1 . In certain cases 

 pyrenoids are subject to variation in number and disposition, but in the 

 great majority of Desmids they are remarkably constant in their relative 

 position. In many instances they have a conspicuous starch sheath (consult 

 fig. 231 A D) and Lutman (10) has shown that all the starch found in the 

 cell of Closterium is originally formed around the pyrenoids. 



Fig. 230. A, Spirot&nia condensata Brb. with a parietal, spirally twisted, band-like chloroplast, 

 x 334. B, Sp. obscura Kalfs, with an axile chloroplast furnished with spirally twisted ridges, 

 x 435. C", zygospore of Sp. truncata Arch., x 250 (after Archer). D, Mesotseniiim De Greyi 

 W. B. Turner, x 435. E and F , M. macrococcum (Kiitz.) Eoy & Biss., x 334 ; note the plate- 

 like chloroplast seen from the flat side in F and from the edge in E. G, zygospore of 

 M. ehlamydosporum De Bary, x 334. H and I, Cylindrocystis Brebissonii Menegh.; H, 

 vegetative cell; I, zygospore; x 435. J, Cosmarium diplosporum (Lund.) Liitkem., x 435. 

 K, Netrium Digitus (Ehrenb.) Itzigsh. & Kothe, showing axile chloroplasts with radiating 

 serrated plates, x 435. 



If Desmids are kept living in small glass vessels for some time, and therefore under 

 abnormal conditions, curious cytological changes occur, resulting in the formation of large 

 vacuoles which previously did not exist. These vacuoles generally contain numbers of 

 minute moving granules which are somewhat different in appearance from those normally 

 present in the apical vacuoles of Closterium. As many as six large vacuoles have been 



1 In a few Desmids, among which may be mentioned Spirotsenia acuta Hilse, Cosmarium 

 subtile (W. & G. S. West) Liitkem. and Cosmocladium constrictum (Arch. Josh., there may be 

 only one pijrenoid in each cell. 



