A STUDY OF HEART-ROT IN WESTERN HEMLOCK. 



21 



more liable to insect and fungus attack. An old tree has many 

 vulnerable points, such as old branches and wounds/' and naturally 

 these injuries open the tree to more and greater infections. Hartig ^' 

 does not believe that old age is a natural inherent condition, but says: 

 "In itself, the feebleness of old age is not a natural condition attribu- 

 table to internal causes. The older a tree is, so much the more 

 numerous are the dangers through which it has had to pass, and so 

 much the greater is the number of its injuries and wounds through 

 which parasites and saprophytes can find an entrance into its inte- 



PiG. 12. — Diagram showing the relation of various factors to the age classes of western hemlock on plats^ 



of the southwestern-slope type. 



rior." From the data secured by questions sent to a large number 

 of lumbermen in the Northwest, it was found that a majority of the 

 answers received indicated that the older age classes of hemlock were 

 very much more defective than the younger. Moller ^ has shown 

 that, with the increase of age in stands infected with Trametes pini, 

 there was a corresponding increase in the percentage of trees infected, 

 and the data given in Table III and figures 11 and 12 also show 

 plainly that with increasing age there is a definite increase in the 

 amount of decay. 



1 Hirtig, R. Textbook of the Diseases of Trees. Translated by William Somerville, p. 7. London 

 and New York, 1894. 



2 Moller, A. IJber die Notwendigkeit und Moglichkeit wirksamer Bekampfung des Kiefembaum- 

 schwammes Trametes piiii (Thore) Fries. In Ztsehr. Forst. u. Jagdw., Jahrg. 36, Heft 11, p. 677-715, 

 2pl. (partly col.). 1904. 



