DISEASES CAUSED BY WOUND FUNGI. 35 



elements to give the lignin reactions. The solution of the middle 

 lamella generally begins near the enlarged pit openings and continues 

 rapidly until the individual fibers fall apart. In the earlier stages of 

 the disease a yellowish substance which is readily soluble in alkalis is 

 present in many of the cells. It is this yellow color which frequently 

 passes outward in advance of the actual destruction of the wood and 

 gives it a darker coloration. In the earlier stages of decay the young 

 mycelium is colorless, but when exposed to the air turns brown. 



PREVENTIVE MEASURES. 



Since Fomes igniarius is a wound parasite, but two methods of pre- 

 vention can be suggested: One of these consists in the prevention of 

 wounds and the other in the removal of the primary sources of infec- 

 tion. On large forest tracts it is at present impossible to deal with 

 individual trees for the purpose of treating wounds. Much can, how- 

 ever, be done in a general way to reduce the chances of natural wound 

 infection. Attention has already been called to the fact that the 

 tendency toward natural pruning in several species of deciduous 

 forest trees, with a consequent rapid healing of the wounds caused by 

 the breaking away of branches, very materially reduces the chances 

 for infection during the early life history of the tree, the period during 

 which the greatest wood development takes place. The growing of 

 straight, clean-stemmed trees results in a healthier stand, in which 

 the chances for infection are very much less than in a similar stand of 

 the same age where the lower branches are left dead on the trees for 

 many years. It is often practicable to assist the natural pruning 

 tendencies of trees, and where this is possible the results will be corre- 

 spondingly great. 



The most practical method "for combating the heart-rot of decidu- 

 ous forest trees at the present time is undoubtedly the removal 

 of the possible sources of infection. This is especially true of more 

 or less circumscribed areas. Wherever the management of forest 

 tracts is undertaken, one of the first things which should be done is 

 to make a careful search for trees already infected and to promptly 

 remove them. 



W Tiere an infected tree is found it should always be cut down. 

 Removing the sporophores from such trees and leaving the trees 

 standing is inadvisable, because when a fruiting body is removed it 

 will soon be renewed, thus necessitating going over the same tract 

 many times, with lessened chances for success. The removal of a 

 diseased tree is furthermore made advisable by the fact that when 

 the sporophores once appear upon such a tree it is a sure sign that 

 the heartwood of that tree is rapidly being destroyed. Where dis- 

 eased trees are cut in the early stages of infection, as evidenced by 



149 



