580 TEXTBOOK OF BOTANY 



of "fleshy " fungi. They may destroy the heartwood, the sapwood, or both 

 ( Fig. 262 ) . Changes in the color and texture of the wood usually accom- 

 pany the growth of the fungi. The internal mycelium is of course the 

 destructive agent through its fonnation of wood-digesting enzymes. 



Fig. 262. Cross section of a stem of white ash in which a saprophytic fungus 

 has destroyed a part of the heartwood. The obvious mycehum pictured on the cut 

 surface grew after the section was removed from the tree and placed in a moist 

 chamber. From U. S. Department of Agriculture. 



The external fruiting bodies (Fig. 247), popularly known as "conks," 

 produce numerous spores, which are carried to other trees primarily by 

 wind. Living trees are infected through wounds, as well as by the 

 direct growth of the fungus from infected stumps into the heartwood 

 of trees in sprout forests. 



It is practically impossible to control wood rot in forests. The infec- 

 tion of orchard trees mav be avoided by careful treatment of wounded 

 trees, and by the eradication of all infected ones. Telephone poles, 

 railroad ties, and other timbers in contact with soil may be protected 

 for long periods of time by appropriate treatment with coal-tar creosote, 

 tar, crude oil, or certain salts of zinc. 



