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AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
surrounding young pockets to a distance of 4 mm., and sparingly to 8 mm. 
in a horizontal direction," while he found scattered mycelium vertically 
beyond the last decay pocket to a distance of 7.8 cm. Meinecke (1914) 
found the advance rot of Echinodontium tinctorum on Abies concolor to 
extend vertically from 2 to 6 feet beyond the typical rot. Weir and Hubert 
(1918), working with the same fungus on Tsuga heterophylla, report ad- 
vance rot recognizable at from I to 5 feet. In these cases a trained ob- 
server can usually recognize the advance made by the fungus by slight 
irregularities in color by streaks. Miinch (1910) working with a sap-rot, 
Stereum piirpureum on poplar, perceived that the advancing hyphae pre- 
ceded the zone of browning to some extent. 
Hartig (1894), speaking of cut timber, suggested long ago that mycelium 
might be expected in. the apparently sound regions of such wood. In the 
lilac. Von Schrenk (1914) emphasizes the sharpness of the line between 
"sound" and completely destroyed wood, and all observers know that this 
is a frequent condition on gross examination. Fomes igniarius on poplar, 
occurring along tamarack swamps in Michigan, shows this contrast most 
markedly. In other heart-rots like that produced by Folyporus hispidus 
and Fomes fraxmophilus on ash, dried-out logs often show a rather in- 
distinct demarcation. But although no generalization can be attempted 
from the one case studied by us, it would seem that others of the heart-rots 
found in the hardwoods might be expected to show advance rot, and perhaps 
to an unsuspected linear extent. The economic importance of this point 
grows in proportion to the scarcity of sound trees, and the temptation to 
inspectors of timber to pass slightly decayed stuff is only too well known by 
our lumber-using manufacturers. If the weakening of the apparently 
sound wood surrounding a narrow core of rot in a large log of valuable 
timber were only half what our test figures show, it might still be of serious 
significance when used for certain structures. 
A very interesting academic question remains to be solved in connection 
with the majority— or at least many — of the heart-rots. What becomes of 
the mycelium in the rotten core inside the black zone? For years, the 
senior writer has had his class in forest pathology attempt to locate mycelium 
in sections of recently cut trees with various heart rots, but in most cases 
the observations ended negatively, even with most persistent efforts. 
Mycelium seems to be lacking in most cases in the advanced stage of the 
rot, or remains only in pockets or cracks as "nests" or "punk," while the 
rotten tissues seem to be free from it. Hypha-holes and corrosion of the 
elements in various degrees are easily observed. As noted in detail, this 
was the situation in the locust tree studied. This, of course, is not true of 
timber attacked by fungi after cutting, nor apparently of sap-rots, working 
from without inwards. But even here our data are not very complete. 
Brown (1915), however, speaking of rot caused by Hymenochaete, says that 
"in an advanced stage of decay only the openings are left as the hyphae 
