24 BULLETIN 871, U. S. DEPARTMENT OF AGRICULTURE. 



Hence, on account of the failure to find any microscopical evidence 

 of fungous action in purple wood, the presence of dry-rot outside the 

 area of purple coloration in certain trees, the frequent occurrence of 

 extensive coloration in trees free from dry-rot, combined with the 

 usual presence of the purple coloration in wood badly enough decayed 

 by Polyporus amarus to cause a noticeable reduction in the merchant- 

 able contents of the individual tree, while it may be more often absent 

 in light infections, the conclusion appeal's obvious that purple colora- 

 tion is not a result of the action of the fungus, but, on the contrary, 

 if it bears any relation whatever to the dry-rot, is merely a condition 

 of the heartwood inducing favorable development of the vegetating 

 hvphas. The fact that the Trarnetes pini decay is more often unac- 

 companied by the coloration is offset by such infections usually being 

 superficial and following wounds which probably exert a profound 

 influence on the heartwood. No relation was found between the 

 purple coloration and the width of the sapwood. Trees with sap- 

 wood varying from very narrow to very broad alike had the colora- 

 tion in the heartwood. 



RELATION OF DRY-ROT TO AGE AND CONDITION OF THE TREE. 



From previous hints in the literature (22, p. 403-406; 23, p. 520; 

 16, p. 18-19, footnotes), Meinecke's preliminary study on incense 

 cedar and his later work on white fir (16), it was reasonable to assume 

 that some relation should exist between dry-rot and the age and 

 condition of the tree; i. e., the degree of dominance and suppression. 



Munch (22, p. 405), working with artificially infected red beech, 

 found suppressed trees more susceptible to decay by Polyporus 

 (Fomes) igniarius, P. (F.) fomentarius, Stereum rugosum, and S. pur- 

 pureum than thrifty, dominant ones and explains this by the theory 

 that the wood of suppressed trees contains a greater amount of air, 

 consequently more oxygen, than thrifty dominants. In previous 

 experiments the same investigator (19, 20, 21) had brought out the 

 strongly favorable influence of oxygen in the host tissues on the 

 development of wood-inhabiting fungi. Meinecke (16, p. 48) recog- 

 nizes three periods in the life of white fir in its relation to the stringy 

 brown-rot caused by the Indian-paint fungus (Echinodontium tinc- 

 torium): (1) The age of infection, at which " the infection rarely leads 

 to more than negligible decay unless the tree is handicapped by quite 

 unusually severe conditions, such as very large old wounds;" (2) the 

 critical age, which "marks the point after which a combination of 

 pronounced suppression and heavy wounding generally results in 

 di-tinct decay;" and (3) the age of decline, "when even dominant 

 (that is, thrifty) trees become subject to extensive and intensive 

 decay." The relation between decay and suppression is brought out. 



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