22 FOREST TREE DISEASES. 



are always suspicious, and while the decay which they 

 very commonly indicate may not in all cases extend 

 very far, it must not be left out of consideration. Decay 

 very frequently extends down the trunk from dead 

 limbs and dead tops. How far the decay extends 

 through the trunk depends very much upon the species 

 of tree and the species of fungus inhabiting it. The 

 resinous pines suffer least; in spike-topped Douglas 

 firs, white firs, and red firs usually one or more upper 

 logs are decayed. In judging a tree every slight swell- 

 ing and depression on the trunk has to be considered, 

 as well as the appearance, color, and quality of the 

 bark. This involves, of course, a thorough knowledge 

 of normal conditions. 



Heartrot is not a disease in the proper sense of the 

 word; the heartwood is dead and thus can not be said 

 to be diseased. Heartrots, however, are extremely im- 

 portant from an economic point of view, and are 

 therefore usually treated as timber diseases. It is often 

 very difficult to diagnose typical heartrot from the out- 

 side. In very many cases the tree outwardly appears 

 to be perfectly healthy, while the heartwood is almost 

 completely destroyed. In seemingly sound white fir 

 logs it is often possible to diagnose decay from the 

 Indian paint fungus by the presence of branch stubs 

 which show the characteristic rusty-red color produced 

 by this fungus ("rusty knots"; see p. 51). 



In our semiarid mountains, many stools (conchs or 

 fruiting bodies, p. 25) of the fungi which cause heart- 

 rot are produced during fall, winter, or spring, and 

 with exception of the harder, more woodlike forms, 



