FUNGI AND FUNGOUS DISEASES OF PLANTS 259 



245. Different forms and habits of mushrooms. While the 

 types of mushrooms already discussed and shown in the illus- 

 trations are probably most common of all, others are almost 



equally abundant. A common form 

 is Polyporus (many pores) (fig. 182), 

 which appears in shelf -like outgrowths 

 from bodies of trees within which 

 its mycelium grows. It is commonly 



FIG. 201. [Basidia and spores 

 of a mushroom 



Magnified 370 diameters. After 

 A. H. R. Buller 



spoken of as one of the 

 tree-destroying fungi. 

 The mycelium is able to 

 penetrate through woody 

 tissues and to extend for 

 great distances within 

 the host plant. It may 

 infect a living tree when 

 a broken limb or other 

 injury offers an entrance, 

 live within it during the 

 life of the tree, and 

 thereafter help to bring 

 about the decay of the 

 tree. The shelf-like re- 

 productive "porETon, in- 

 stead of bearing gills 

 on the under surface, 



has many small pores within which spores are formed. The 



number of these spores is very great ; one authority 1 estimates 



1 Buller, A. H. R., Researches on Fungi. Longmans, Green & Co., 1909. 



FIG. 202. Puffballs 



Two species of puff balls of the genus Lycoperdon. 



Those above are one half natural size ; that 



below is two ninths natural size 



