THE FUNGI 



273 



smooth or greatly roughened surfaces, but in the more common 

 species they line pores on the under side of the shelflike fruit 

 body. Since these pores open 

 out on the under surface of the 

 fungus, the spores are readily 

 disseminated, as in the mush- 

 room, by being shot off from 

 the basidia into the open space 

 of the pores, from which they 

 fall downward into the open air. 

 The bracket fungi are often 

 very hard and woody, but sec- 

 tions cut from the plant body 

 show that it is composed en- 

 tirely of thickened hyphse. 

 The feeding mycelium pene- 

 trates and absorbs food from 

 rotten logs and stumps in the 

 saprophytic species, but in the 

 parasitic forms, which are so 

 destructive to forest trees, the 

 mycelium penetrates into the 

 living tissues of the tree and 

 destroys it (Fig. 152). This 

 penetration of the hyphse into 

 the hard wood of trees usually 

 begins at a wound on the ex- 

 posed surface of the trunk or 

 branches, and its entrance into 

 the tree is effected by the se- The fi s ure shows the m y celium of Pol v- 



* porus squamosus penetrating and break- 



cretion of Cellulose and wood ing down the wood-cell walls by digestion, 

 ferments, which digest a pas- From Duggar's "Plant ^ Diseases." After 



sage for the hyhse. Once within 



the tree, these hyphse branch within its tissues and not only 

 break down the wood-cell walls but attack the living cells of 

 the tree and their stored food. The bracket fungi thus destroy 

 living forest trees and logs, railroad ties, and lumber. 



FIG. 152. Destruction of wood by 

 fun s us 



