FUNGI: SAC FUNGI 



26 S 



become centers in the protoplasm for the formation of eight 

 ascospores. 



Fig. 225. 



Contact of antheridium 

 and carpogonium (car- 

 pogonium the larger 

 cell); beginning of fertili- 

 zation. 



Fig. 226. 



Disappearance of con- 

 tact walls of antheri- 

 dium and carpogonium, 

 and fusion of the two 

 nuclei. 



Fig. 227. 



Fertilized egg sur- 

 rounded by the envelop- 

 ing threads which grow 

 up around it. 



Figs. 225-227. Fertilization in Sphaerotheca; one of the powdery mildews. (After 

 Harper.) 



427. The black fungi (Sphaeriales). The black fungi 

 include a vast number of the sac fungi, with many genera and 

 species. The fruit bodies (perithecia) 

 are black or dark brown; they occur 

 singly, in- troops or in masses, and 

 sometimes are imbedded in a black 

 stroma (a compact sterile fungus 

 tissue). Many are saprophytes and 

 many others are parasites on other 

 plants, causing leaf spots, blights, 

 rots, cankers, knots, etc. Many of 

 these produce serious diseases of 

 vegetables, farm crops, orchard and 

 forest trees. Many of them have 

 " imperfect " stages on which asexual 

 spores (called conidia) are borne on 

 free hyphae of a great variety of form Fi s- 228 - 



. . . Black knot of plum (Plowrightia 



and association, or in Other Cases morbosa), showing deformities of the 



stems. 



the asexual spores are borne on snort 



hyphse enclosed in bottle-shaped or oval cases resembling the 



sac fruit bodies. The perfect stage is represented by the true sac 



