TREES AND TIMBER 427 



The point of attack is always the root, through the heart 

 of which invasion is made into the trunk. This often leads 

 to one-sided decay of the trunk's heartwood. The wood is 

 rendered very brittle, yellow, and later of cheesy character, 

 so that it tan readily be cut cross grain when wet or re- 

 duced to a powder when dry. 



The pore-bearing sporophores, which appear in July or 

 August, are from 10-35 cm. across, growing either from the 

 roots or the trunk. If from the trunk, they are sessile ; 

 from the roots, stalked. The fresh spore layer is rose-col- 

 ored, and turns dark red if bruised. 



This disease is very common throughout northern for- 

 ests. In Europe, where it is greatly dreaded, it is cus- 

 tomary to prevent its spread by trenching. Groups of 

 infected trees and trees near them may be cut to advan- 

 tage to protect other trees. 



Root rot, ozoniose {Ozonmm omnivorum Shear). — 

 Elm, basswood, oak, cottonwood,' mesquite, china tree, 

 mulberry, apple, and pear are affected by this rot, which 

 has been described and discussed on page 401. 



Root rot, dematophorose {Dematophora necatrix Hartig). 

 — A disease described on page 172 affects a large number 

 of species of trees, among them mulberry, fig, apple, pear, 

 and cherry, as well as many wild species. 



Thelephorose (Thelephora galactina Fr.) . — Noted in 

 the Ozarks primarily upon the oak, but attacking fruit 

 trees as well, this rot much resembles dematophorose. 



DECAY OF DEAD TREES OR DEAD PARTS 



While decay of dead trees cannot be regarded strictly 

 as a condition of disease, but rather as a post-mortem 



