24 BULLETIN 871, IT. 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 appears 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 
hyphte. The fact that the Trametes 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 sap wood. 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) ignzarius, 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 (EcJiinodontium tine- 
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; 7 ' (2) the 
critical age, which "marks the point after which a combination of 
pronounced suppression and heavy wounding generally results in 
distinct 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. 
