b. DISEASES OF COITISSROUS TRESS. 



The natural forests of the greater part of the western United 

 Stu.t '-o consist almost entirely of coniferous trees. The annual 

 lose from wood-rotting fungi in the national forests amounts to % 

 very large item. An average of 2 to 10 per cent of the mature 

 trees in all the forests are attacked and rendered worthless. In 

 some localities certain species, for example Pinus monticola, Tsuga 

 heterophylla, Abies grandis, A. lasiocarpa, and Pseudotsuga taxi- 

 folia suffer to the extent of 50 to 75 per cent of the total stand 



in lumber feet. 



The most destructive disease of the hear two od of conifers is 

 caused by Trametes pini (3rot.) IT. This fungus is not equally 

 prevalent in all localities on the same species. It probably at- 

 tacks nearly all species of conifers in the United States, except 

 the junipers. The progress of the rot through the tree trunks is 

 not very rapid, but the final effect is certain, as in the end it 

 usually destroys the whole heart of the trunks and of portions of 

 the limbs. In some instances trees are killed outright, but in 

 the majority of cases they are so weakened by the fungus that they av, 

 broken off by the wind. This fungus rots the lieartwood of the roots 

 of trees also, and sometimes is communicated from tree to tree 

 underground, where large roots of separate trees are in direct con- 

 tact, thus passing from a diseased root to a healthy one. 



The following species of trees are attacked by Trametea P : 

 or its subspecies: Abies balsamea, A. concolor, A. lasiocarpa , 

 A. nobilis, Larix laricina, L. occidental, Picea enfeelmanni, 

 P. mariana, P. rubens, P. sitchensis, Pinus contorta, P. echinata 



