A STUDY OF HEART-ROT IN WESTERN HEMLOCK. 31 



natural weakness in healing injuries, producing resin, etc., combined 

 with environmental factors is responsible for the intensive and 

 extensive fungous activity within this species of tree. At the same 

 time it must be borne in mind, especially in the case of hemlock, 

 that such a natural trait as the absence of any great amount of 

 protective resin must be considered as playing an important part 

 in the entrance of the disease. The foregoing data have clearly 

 shown that one fungus is responsible for almost the entire amount 

 of heart-rot found in western hemlock, that the river-bottom type 

 exhibits more decay than the other (comparing the youngest age 

 class), that this type also exhibits a remarkably early decay, and 

 that as a whole a large amount of heart-rot is found in hemlock at 

 early periods in its life. 



Dense stands growing in moist, poorly drained soils develop a 

 large number of suppressed or low- vigor trees. This is more com- 

 monly the case when the stand is overtopped by older trees of 

 other species. The low vigor due to the overshading of the lower 

 crown causes " the early and numerous formation of shade-killed 

 branches. These in time produce branch stubs which are believed 

 to be responsible for most infections by Echinodontium tinctorium. 

 The shading of the crown, especially the lower crown, not only 

 causes the eventual formation of branch stubs but produces a moisture 

 and shade condition favorable to the germination and entrance of 

 the fungus. As a theory of infection for hemlock types, this is 

 corroborated by the fact that in thinnings made by cutting out the 

 more merchantable species the secondary crowns formed rapidly and 

 vigorously by an enlargement and thickening of the regular crown. 

 This fact, coupled with the observation that very few living sporo- 

 phores were found 10 years after the thinning, strengthens the theory. 



DISCUSSION OF RESULTS. 



As a preliminary to the discussion of the main points brought out 

 in the foregoing pages, it is essential to review briefly the main 

 silvicultural characteristics of the tree in question. It will then be 

 easier to point out the importance of the various factors influencing 

 decay and to arrive at certain conclusions regarding the action of 

 the fungus Echinodontium tinctorium during its life history on the 

 host. 



The western hemlock, as indicated by its distribution, requires a 

 cool and moist climate for its development, and an important fact 

 in this connection is its splendid maximum development along the 

 western slope of the coast ranges, where it receives an annual rain- 

 fall of from 70 to 100 inches.^ 



1 Allen, E. T. The western hemlock. IT. S. Dept. Agr., Bm-. of Forestry Bui. 33, p. 10. 1902. 



