THE GREEN ALG.E 



479 



Fig. 310. — Grape Desmid. Germination of zygospore: A, protoplast 

 emerging; B, protoplast beginning to divide in half; C, division nearly 

 complete; D, division complete within the thin temporary cell-wall; 

 E. the two desmids escaped from the wall; F, one of them dividing by 

 fission; G, the fission nearly complete, ^f. (DeBary.) 



Fig. 311. — Pond-scum {Spirogyra sp., Pond-scum Family, Zygnemacece). 

 1, segments of two thread-like plants beginning to conjugate by the 

 protrusion of adjacent cell-walls toward each other. 2, later stages 

 resulting in the formation of a zygospore (6). Much magnified. (Ker- 

 ner.) — Pond-scums abound on the surface of ponds, forming masses 

 of bright green color through the summer which turn brownish toward 

 spring when conjugation takes place. 



