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) 



266. 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 



