THE GREEN ALG 479 
Fic. 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, 422. (DeBary.) 
Fic. 311.—Pond-scum (Spirogyra sp., Pond-scum Family, Zygnemacee). 
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 (b). 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. 
