i84 PLANT DISEASES 



converted into cellulose and used by the fungus as food. 

 Hartig states that in the Scots fir the disease does not pass 

 from the root up into the trunk ; this is considered to be 

 due to the abundance of resin, more especially in the lower 

 part of the stem, which prevents the upward extension of 

 the mycelium, whereas in the spruce and Weymouth pine, 

 which contain but little resin, the rot extends high up the 

 trunk. During the progress of the disease flat sporophores 

 are formed on the underground roots ; whereas, after the 

 tree is dead, more highly developed sporophores develop 

 on and around the base of the stump. 



The sporophore is extremely variable in size and form ; 

 sometimes, as already stated, resembling a thin white cake, 

 half to one inch across, with the white hymenium upper- 

 most. 



In the above-ground condition the fungus resembles a 

 white crust attached to, and following the irregularities of, 

 the wood, producing here and there a free, projecting 

 portion, or several of these overlapping. The upper surface 

 is brown, and very irregularly tuberculose and wrinkled, 

 the white hymenium being situated on the under surface 

 of such free, projecting portions. The pores are minute 

 and rounded. The whole fungus is woody and hard, and 

 sometimes reaches to six inches across. 



Preventive Means. — Diseased trees should be removed 

 at once, and the site isolated by a narrow trench, taking 

 care to include within the trench all roots of the diseased 

 tree, as Hartig has demonstrated that where the root of a 

 healthy tree is in contact with a diseased root, the fungus 

 can pass from one to the other. 



The sporophores should be collected and burned when- 

 ever they appear, as their frequent occurrence on roots 



