INCENSE CEDAR. 29 
ENEMIES. 
DISEASE. 1 
Incense cedar is subject to few diseases, but three of these are 
very common. They are caused by a mistletoe (Phoradendron juni- 
perinum Ubooedri), a rust fungus (Gymnosporangiurw blasdalea- 
num), and the dry-rot fungus (Polyporus amarus). The only seri- 
ous damage to merchantable trees, however, is due to the latter. 
Polyporus amarus attacks the heartwood of mature living trees 
only, trees below the age of 140 years being more or less im- 
mune. Thrifty growing trees in damp, rich soils seem to be less 
affected than slow-growing ones on dry, poor sites; and trees with 
large wounds are far more likely to be pecky than intact ones. 
The large annual fruiting bodies (sporophores or conchs) of Poly- 
porous amarus invariably grow out of branch holes or pin knots, never 
through the bark. The mature conch has the shape of a bell cut 
lengthwise in halves. The upper side is light tan in color, the under 
side a brilliant yellow, turning brown with age. Spores are formed 
in enormous numbers and are carried by air currents to other trees. 
They germinates only when they land on a wound or opening lead- 
ing to the heartwood. Thus fire scars and branch stubs very often 
offer them an easy entrance. The fungus attacks the heartwood, 
honeycombing it with cavities from one-quarter inch to an inch in 
diameter by from an inch to several feet in length. These cavities 
are filled with a dry, brown, charcoal-like substance which char- 
acterizes this defect and gives it its name of " dry" or "brown" rot. 
The wood between the cavities is usually sound. 
It is often impossible to detect the presence of dry-rot from the 
outward appearance of the tree, but there are certain infallible signs 
by which we can tell that the timber is infected. The presence of 
a fruiting body of Polyporus amarus, of course, indicates beyond a 
doubt that the fungus is at work in the heartwood. But the fleshy 
annual fruiting bodies are devoured eagerly by squirrels and the 
larvae of a small moth that afterwards burrows through into the 
dead bark. Later, woodpeckers chop out these larvae, so that, finally, 
a cup-shaped depression, pierced with numerous larvae holes, is 
formed in the bark where the fruiting body once was. These de- 
pressions are a certain sign of decay, and their number and appear- 
ance indicate the extent of the dry-rot in the interior of the tree. In 
general, the decay is more pronounced in the lower part of the tree, 
since the fungus very commonly starts from fire scars. 
Since the entrance of the dry-rot fungus into the heartwood can 
in a great number of cases be traced to fire scars, fire prevention and 
1 Prepared by Dr. E. P. Meinecke, pathologist, Bureau of Plant Industry. 
