THE GREEN ALG^E 



477 



Fig. 307. — Wall-stain Alga {Plcurococcus vulgaris, Wall-stain Family, 

 Pleurococcacea;) . Plants showing fission in various directions, ^i^. 

 (Wille.) — Growing commonly upon moist rocks, bricks, and tree- 

 trunks, forming extensive green-stains, throughout the world. 



Fig. 308. — Grape Desmid (Cosmarium Botrys, Dcsmid Family, Desmidiacece.) 

 I-III, stages of fission, ^l"-. (DeBary.) — Bright green. Common in 

 fresh water. 



il .7 



■f . A 



kJ.-^^1 



Fig. 309. — Grape Desmid. A, first stage in conjugation; the two halves of 

 the celi-wall (b) have been broken apart by the protruding protoplast 

 (c). B, later stage; the protoplasts of two plants are coming together. 

 C, final stage; the two protoplasts have fused into one mass to form a 

 zygospore (/) leaving the old cell-walls (c, b) empty. D, E, F, stages 

 in the ripening of the zygospore which surrounds itself with a pro- 

 tective wall from which numerous projections finally arise, ^^ (De- 

 Bary.) 



