THE FUNGI 



253 



on account of their economic importance. Forms differ- 

 ing enormously in general appearance, size, and life habits 

 are included in this class. 



Here belong two genera of large, edible fungi, the morel 

 (Figs. 176, 177) and the truffle. Many injurious genera 

 are found, some of them saprophytes 

 and others parasites. Best known 

 among the former are the green and 

 the yellow molds, more properly 

 called mildews (Fig. 175). A few ex- 

 amples of the latter are the grape- 

 vine mildew, the black-knot fungus of 

 plum and cherry trees, the peach-curl 

 fungus, the bitter rot of apples, the 

 brown rot of peaches, and the plum 

 pocket fungus. 



LICHEXS, SAC FUNGI AS MESS- 

 MATES AVITII ALG.E 



327. Definition, Occurrence. 



— Lichens (Figs. 178, 179) were 

 formerly supposed to be a dis- 

 tinct class of plants, and it is less 

 than forty years since their real 

 nature began to be understood. 

 A lichen is a combination of tiro 

 plants. The green cells, called the gonidia (Fig. 180, g), be- 

 long to some species of alga, and the remainder, the larger 

 portion of the growth, is a fungus (usually a sac fungus) 

 parasitic upon that alga. The groups of lichens correspond 

 in structure to certain groups of fungi, but the genera are 



Fig. 177. A Vertical Section of 

 the Spore-Bearing Surface of 

 Fig. 176. (x 240.) 



u, asci, or spore-sacs; m, myce- 

 lium ; p, paraphyses, or sterile 

 filaments. 



