228 THE SAC FUNGI 



of these discharging sporangia, it would become ' infested and 

 later, branches of the hyphae would project from its body and 

 repeat the process of sporangia formation. 



CLASS B. ASCOMYCETES OR SAC FUNGI 

 82. General Characters. The Ascomycetes are the largest and 

 most variable group of the fungi. They are illustrated by the 

 powdery mildews which affect the leaves of a variety of plants; 

 the brown and blue moulds that occur on preserves, decaying 

 fruit, old leather, etc. (Fig. 138); the cup fungi and morels 

 (Figs. 139, 141); the black knot of the cherry and plum trees 

 (Fig. 149), and the ergot of rye, etc. 



The plant body or mycelium resembles in structure that of 

 preceding orders, but its hyphae are composed of numerous cells 

 instead of being tubular or with few cross walls as in the Phyco- 

 mycetes (Fig. 138). The sporangia (Fig. 152) are reduced in 



FIG. 138. The green mould, Penicillium, one of the most common of the 

 Sac Fungi. The hyphae of the branching mycelium is composed of cells 

 and the spores or conidia are formed in chains that are arranged in brush- 

 like clusters at the ends of the erect hyphae. 



size and contain but a single spore each, which is never dis- 

 charged from the sporangium. This body will be referred to 

 in the future as a spore or conidium (plu. conidia). 



The gametangia are suggestive of those noted in the red algae 

 (Fig. 140), though in many forms they appear to be greatly re- 

 duced or even lacking. The fusion of the gametes results in the 

 formation of a gametospore which germinates at once, forming in 



