STRUCTURE AND LIFE HISTORIES 
264. Other Sac -fungi. Between 25,00x5 and 30,00x3 
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 
