A STUDY OF HEART-ROT IN WESTERN HEMLOCK. ) 
always indicate the true condition. Moist sites of various slopes 
and exposures are generally found to produce a greater development 
of decay, and invariably the older trees in such stands are badly 
infected. This is indicated by the data secured from lumbermen 
given in the pages that follow. The early formation of branch stubs 
through the premature dying of the lower crown due to overshad- 
ing can always be depended upon as an indication of existing decay, 
and it will usually be found that the center of infection is located in 
that portion of the trunk bearing the largest number of dead branches 
or branch stubs. The presence of many branch stubs, the presence of 
branch stubs show- 
ing unmistakable rot 
colorations, the ap- 
pearance and num- 
ber of sporophores, 
Many injuries (in- 
cluding frost cracks), 
old age, and unmis- 
takable signs of re- 
duced vigor are all 
very reliable indica- 
tions upon which a 
marking officer may 
learn to base his judg- 
ment for the deter- 
mination of decay in 
western hemlock. 
GENERAL CHARACTERIS- 
TICS OF THE ROT. 
The spores of 
E E i Fic. 6.—Cross section of a young hemlock, showing heart-rot at a 
Echinodontium tinc- whorl ofbranch stubs. In this case there are five dead branch stubs, 
torium upon germi- all of which were possible agencies in conveying the disease into 
é the heartwood. 
nation penetrate the 
host mainly through the dead broken branches or branch stubs 
(figs. 6 and 7). This has been confirmed by the data taken in the 
study of the relation of injuries to decay. A few infections are trace- 
able to fire and logging scars, frost cracks, or other injuries.- In a 
few instances, on areas other than those upon which data were 
secured, it has been found that the burls on hemlock caused by 
Razoumofskya tsugensis were points of infection. 
The hyphz on germinating follow the central nonresinous heart- 
wood zone of the branch stubs and continue inward to the main 
heartwood of the tree (fig. 8), spreading more or less uniformly up 
and down the trunk from the point of infection. The decay is char- 
63424°—18—Bull. 722-2 
