THE CiREEN ALUM 



477 



Fiu. 307. — Wall-stain Alga {Plcurococcus vuloaris. Wall-stain Family, 

 Plcurococcacece).^ Plants showing fission in various directions, ^t"- 

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

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



Fig. 308. — Grape Desmid {Cosmarium Botrys, Desmid Family, Desmidiacew.) 

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

 fresh water. 





Fig. 309. — Grape Desmid. .1, first stage in conjugation; the two halves of 

 the celi-wall (6) 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 (e, b) empty. D, E, F, stages 

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

 tective wall from which numerous projections finallv arise, ^1'*- (De- 

 Bary.) 



