A STUDY OF HEAET-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 immis- 

 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 o f 

 EcTiinodontium tinc- 

 torium upon germi- 

 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 

 Uazoumofskya tsugensis were points of infection. 



The hyphse 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 



Fig. 6. — Cross section of a young hemlock, showing heart-rot at a 

 whorl of branch stubs . In this case there are five dead branch stubs, 

 all of which were possible agencies in conveying the disease into 

 the heartwood. 



