THE GREEN ALGA4 477 
Fic. 307.—Wall-stain Alga (Pleurococcus vulgaris, Wall-stain Family, 
Pleurococcacee). Plants showing fission in various directions, *#2. 
(Wille.)—Growing commonly upon moist rocks, bricks, and tree- 
trunks, forming extensive green-stains, throughout the world. 
Fic. 308.—Grape Desmid (Cosmarium Botrys, Desmid Family, Desmidiacee.) 
I-III, stages of fission, 232. (DeBary.)—Bright green. Common in 
fresh water. 
Fic. 309.—Grape Desmid. 4, first stage in conjugation; the two halves of 
the cell-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 (f) leaving the old cell-walls (e, 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, 292 (De- 
Bary.) 
