128 A MANUAL OF FORESTRY 



stands thinnings are advisable to reduce the proportion of 

 diseased trees and strengthen those that remain. The practice 

 which has been inaugurated by some lumbermen of leaving for 

 seed purposes trees diseased with red rot is unsafe because it 

 tends to perpetuate the disease, not through the seed of the old 

 trees, but by the fungus upon them. 



Poly porn s schweinitzii . 



This fungus is common on balsam, red and white spruce, 

 white pine and arborvitae; it attacks living trees of all ages and 

 causes extensive losses. 



The fungus first enters underground, through the root system, 

 but soon spreads to the trunk, up which it may extend its growth 

 for forty feet or more. Diseased trees are ordinarily found in 

 groups, because the fungus spreads from tree to tree through 

 the ground. As the disease progresses the root system and 

 trunk become weakened and finally the tree is uprooted or 

 broken off near the base. 



Like Trametes pini this fungus destroys the lumber value of 

 the infected portion. Probably the greatest loss is found in 

 the balsam, of which species nearly all the older trees are 

 attacked. 



Wood attacked by Polyporus schweinitzii 1 has a cheesy con- 

 sistency, is yellowish in color and is easily powdered when 

 dry. In the last stages of decay it is very brittle. These char- 

 acteristics of the diseased wood and the large, brightly colored 

 fruiting bodies are the best means of field identification. The 

 fruiting bodies when young are a yellowish-brown color, but in 

 a few days become reddish brown. The underside is some- 

 times rose colored, and if bruised, quickly turns dark red. They 

 take the form of brackets, ordinarily several in number, fastened 

 one above the other, usually arising from the roots of the tree, 

 near the base of which they may be seen growing, in the months 



1 For a more detailed description of tin- fun^u* see Bull. 25, U. S. Division of 

 Vegetable Physiology and Pathology, entitled, "Some Diseases of New England 

 Conifers," by Von Schrenk. 



