456 



THE FUNGI WHICH CAUSE PLANT DISEASE 



but sometimes thin or even lacking; gills touching broadly or 

 running down the stem, whitish or yellowish; spores elliptic or 

 rounded, 7-10 m- 



This is a common wound parasite of conifers and deciduous 

 trees, causing a root-rot. It also causes a potato disease in Aus- 

 tralia.'"* The abundant mycelium is white and extends a meter 



Fig. 324. — Pleurotus ostreatus. After Clements. 



or more through the wood and bark, aggregating imder or on the 

 bark to form shining hard gray-black intertangled cords (rhizo- 

 morphs) 1-2 mm. in diameter often reaching out to great distances 

 through the earth. Fig. 326. Sheets of white felt also occur. 



The young mycelium grows into the cambium layer, attacking 

 living cells and often encircling the tree. In the living cortex it 

 presents a characteristic fasciated skin-like appearance. 



