272 



STRUCTURE AND LIFE HISTORIES 



264. Other Sac -fungi. — Between 25,000 and 30,000 

 species of sac-fungi have been described. Some of them 

 are filamentous, like the lilac-mildew, while some are 

 fleshy, like the common "cup-fungi" (Fig. 196). The 

 edible morel, Morchella esculenta, (Fig. 197) is an Asco- 

 mycete, and the common yeast referred to in the chapter 

 on fermentation (Fig. 60) is also classed here because, in 

 one of its methods of reproduction the unicellular plant 



Fig. 197. — The morel, Morchella esculenta. (Photo by W. A. Murrill.) 



body functions as a spore-mother-cell, the protoplast 

 becoming organized into spores (ascospores) , and the wall 

 of the mother-cell serving as an ascus. 



A "RUST" FUNGUS (WHEAT RUST) 



265. Importance. — One of the most important, as well 

 as most difficult, fungi to understand is the wheat rust 

 {Puccinia graminis). This fungus is important because 



