38 DISEASES OF DECIDUOUS FOREST TREES. 



The fruiting bodies of Polyporus sulphureus usually occur in some 

 large knot hole on the side of the tree trunk; they are, however, 

 frequently found on stumps and fallen branches. The mycelium of 

 the fungus is capable of living in the dead wood of a tree for many 

 years, and when the proper conditions recur the fruiting bodies con- 

 tinue to form each year, or with a marked periodicity in alternate 

 years. A large branch was broken from a chestnut tree which had 

 been diseased by the sulphur polyporus for many years, and accu- 

 rate observations were made upon this branch for five years. It 

 was found that in July or August large masses of the fruiting bodies 

 developed from this branch. The fruiting bodies of the sulphur 

 polyporus form on trees and stumps during the middle or latter part 

 of the summer and, as stated, can be found for only a short time. 



The destruction which Polyporus sulphureus brings about in the 

 heartwood of trees is very similar for all of the host trees upon which 

 it grows, irrespective of whether they are coniferous or deciduous 

 species. The decayed wood resembles a mass of red-brow T n charcoal. 

 There are various degrees of coloration, depending upon the host, 

 being darker in most of the species of oak and lighter in chestnut 

 and walnut. The decayed wood is characterized by a series of con- 

 centric and radial cracks extending irregularly through it. (PI. IV, 

 fig. 2.) These cracks develop as the wood is destroyed, and are 

 caused by the decrease in volume of the affected wood. The fungus 

 forms thin, leathery sheets in the cracks. In wood which is badly 

 decayed a blow with a hammer will cause the decayed wood to drop 

 out in the form of fine powder, leaving the thin sheets, consisting of 

 densely interwoven threads of the fungus, as a skeleton framework. 

 The decay of the wood itself is a very uniform one; in other words, 

 there is no localized decay, but the wood is uniformly converted into 

 a brown, brittle substance which readily crumbles into a fine powder 

 when rubbed between the fingers. The red-brown coloration, the 

 presence of large white sheets extending throughout the mass of the 

 decayed wood, and the presence of numerous large and small eracks 

 extending radially, tangentially, and transversely through the mass 

 of decayed wood readily enable one to recognize wood destroyed by 

 the sulphur polyporus. In the oaks the broad medullary rays persist 

 longest. 



The age at which trees are attacked by this fungus varies consid- 

 erably with the region in which they are growing and the conditions 

 under which they are situated. Healthy, rapidly growing trees which 

 heal their wounds quickly remain free from the disease much longer 

 than stunted, poorly grown trees. The youngest trees in which the 

 red heart-rot was found were about 50 years old. 



Preventive measures consist of essentially the same treatment as 

 is suggested for Fomes igniarius. In view of the fact that the myce- 



141) 



