456 A TEXTBOOK OF BOTANY [On. X 



perithecia extend long, hyphal branches ending in hooks 

 of characteristic forms : and the different species are marked 

 by a striking variety in details of the ends of these branches. 

 The perithecia remain in place until the leaves fall, after 



FIG. 318. Microsphcera Alni. 



Left, a perithecium, with the characteristic appendages, and right, a 

 perithecium releasing the asci ; X 200. Above, an ascus, with ascospores ; 

 X400. 



which, in the next spring, the ascospores are released by the 

 decay of the hard inclosing walls. 



ORDER 4- PLECTASCALES : THE BLUE AND GREEN MOLDS. 

 These plants are well described by their common name, for 

 while superficially they resemble the true, or Black, Molds 

 already considered under Zygomycetes (page 437), they 

 produce bluish or greenish, instead of blackish, spore masses. 

 They occur among the Black Molds, but extend more widely 

 than they, to almost all kinds of damp organic bodies, - 

 including cheese, leather, wall paper, and 1 nearly anything 

 that will "mold" in dampness. Some 250 species are 

 known, all saprophytes of minor economic importance. 



