H 



OUTLINES OF PLANT LIFE. 



zag chains, or even branched filaments {h, i, fig. ii). 

 Other sorts may be attached singly or in clusters by a gelati- 

 nous stalk {e, fig. ii). In all cases the jelly, like the rest 

 of the cell-wall, is a product of the protoplasm. The slow 

 gliding movements of some free diatoms are due to the pro- 

 trusion of strands of protoplasm through slits in the valves. 



Fig. 13.— Various desmids. a, Micrasterias : i, Cosmarium : c, Xanthidium : 

 d, Clasterium : t, Staurastrum ; f, Aptogonum. Magnified about aoo diam. 

 —After Kemer. 



19. The desmids. — These form another group of one- 

 celled green algae. They have neither the brownish color 

 nor siliceous wall characteristic of diatoms, but are bright 

 green cells of remarkably diverse and often beautiful forms. 

 As a rule the cell is flattened and is divided almost into two 

 by a deep constriction near the middle {a, b, c, e, fig. 13). 

 Often the body of the cell is covered with warts or spine-like 



