32 BULLETIN 275, U. S. DEPARTMENT OF AGRICULTURE. 



Other causes of serious wounds are comparatively rare. Occasion- 

 ally a falling tree will brush off part of the bark of its neighbor. If 

 the wound is large, the exposed sapwood dries out, cracks, and the 

 heartwood becomes exposed. Very rarely a living tree shows signs 

 of early girdling by rodents. Girdled trees as a rule are killed within 

 a short tune. 



With very few exceptions the entrance of the fungus into the tree 

 can be traced to one or more of the wounds just discussed. Occa- 

 sionally, however, a tree showing no wounding at all is found to be 

 decayed. In such cases the only means of entrance for the wood- 

 destroying organism is through knots. 



White fir prunes itself very poorly; the wood of the twigs is tough, 

 hard, and resistant, and the branches do not break off very readily. 

 Later, dead twigs may break off; in the cracks of the wood of the 

 stubs spores of fungi may find proper conditions for germination and, 

 once established, use the pin knot as a bridge from the exterior of the 

 tree through the bark and sapwood into the heartwood. This is par- 

 ticularly true for twigs in which heartwood formation has begun. In 

 this sense the opening afforded to fungi by a pin knot that is not 

 healed over may be likened to a wound. The opening formed by the 

 pin knot, however, is too small to materially influence the chemistry 

 and physics of the heartwood of the tree. 



White fir is not exposed to a great number of heart-rot fungi. 

 Polyporus schweinitzii is not common. Polyporus sulphureus and 

 Trametes pini are rather rare. The parasitism of Fomes pinicola is 

 not fully established, at least not in white fir. The writer has found 

 it on thrifty sugar pine in central California, where it was undoubt- 

 edly parasitic in the sense of attacking the sound heartwood of living 

 trees through an open fire scar and extending toward the sapwood. 

 There would be no incongruity in assuming that it may also occur 

 parasitically on white fir; in fact, a number of observations rather 

 speak for the correctness of this assumption. 



By far the most serious danger to white fir throughout its range 

 comes from Echinodontium tinctorium Ellis and Ev. This fungus 

 seems to be particularly adapted to Abies concolor and does not 

 appear on many other species. In California it is, though not very 

 often, found on Abies magnified sJiastensis and also rarely on Douglas 

 fir. This fungus must therefore be considered as the chief fungus 

 enemy of white fir. The sporophores are easily recognized. They 

 are rather large, from 2 to 10, 12, and more inches in width (measured 

 horizontally from side to side where they are attached to the tree), 

 distinctly hoof shaped, with a black, dull, cracked, rough upper sur- 

 face, and a lighter, grayish, level under surface, which is thickly set 

 with hard, coarse spines. In young specimens the under surface is 

 whitish and rather daedaloid prior to breaking up into spines. The 



