32 BULLETIN 722, U. S. DEPARTMENT OF AGRICULTURE. 
Its moisture requirements seem to be the principal limiting factor 
of its distribution, since it is found growing on a variety of soils. 
lts altitudinal range extends from sea level in Alaska, British Colum- 
bia, Washington, and Oregon to an altitude of 6,000 feet, and in 
Idaho and western Montana it is found at a maximum altitude of 
5,000 feet. Itis always at its best in cool moist draws or north slopes. 
Regions with a relatively high humidity favor its development, 
although at some of the higher altitudes the humidity is much less 
than in the bottom-land sites. 
A very tolerant species, it is found to thrive in Idaho and Montana 
in the white-pine type, generally in a mixed stand. Referring to its 
tolerance, Sudworth ‘ says it is ““very tolerant of shade throughout 
life, especially in seedling stages. In later life vertical light is neces- 
sary for best growth. Allowed overhead light, it recovers remarkably 
well from long suppression and renews rate of growth. Prolonged 
suppression in dense shade greatly checks growth. It thrives in cool, 
open, humid places with abundant soil moisture.” 
No natural thinning takes place under normal conditions, and in 
mixed stands the pruning of the lower branches is a slow and imper- 
fect process. Shade causes the lower branches of the crown to die, 
and these remain on the trunk until broken by wind, windfalls, or 
other causes. This condition leaves the tree with a large number of 
branch stubs open to infection by fungous spores. ‘ 
Hemlock in its green condition contains 40 to 60 per cent of its own 
dry weight of moisture,? a relatively large amount compared to the 
other trees of the region. This fact has a direct bearing upon the 
action of the fungus in the heartwood and accounts for the water- 
logged condition of the base of the tree which is often encountered in 
stands growing on poorly drained soils. 
In summing up the points brought out by this study the most pro- 
nounced results are found in the variations in the action of the decay 
in the two types studied. A glance at the plat descriptions given for 
each type (Table I) will show the variation in slope and exposure as 
well as the marked difference in soil and atmospheric moisture. The 
river-bottom type, growing as a dense suppressed stand on a heavy 
undrained soil in close proximity to the river and to its numerous 
sloughs, presupposes its greater susceptibility to the attack of the 
fungus. In the absence of trees of an older age class it can only be 
assumed that the rot percentage would increase with age. The fact 
that the rot percentage in the older age class was lower does not 
invalidate this assumption in view of the small number of trees it 
1 Sudworth, G. B. Forest trees of the Pacific Slope, p. 95. 1908 Published by U.S. Depariment of 
Agriculture, Forest Service. 
2 Hanzlik, E. J., and Oakleaf, H. B. Western hemlock; its forest characteristics, properties, and uses. 
In Timberman, rv. 15, no. 12, 1914, p. 235-33, tab. 3. 
