40. BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 
summer wood is scarcely affected. In this condition the wood sep- 
arates readily along the annual rings. , 
Hardwood logs and lumber.—Certain fungi (Polystictus versi- 
color (L.) Fr., Sterewm hirsutwm (Willd.) Pers., and others) cause a 
sap rot very difficult of detection in its incipient stage. The typical 
decay is very hght in weight, white in color, rather soft, and easily 
broken in the hands. But since the first indication of this decay is 
a faint whitening of the diseased wood and white is the normal 
color of most sapwoods, it is apparent that the initial stages may 
be readily overlooked. At the same time the wood is decidedly re- © 
duced in strength. The decay is most common on hardwoods, but 
also occurs to some extent on softwoods. Fortunately none of the 
fungi causing this white sap-rot attack living trees of the species 
which furnish airplane timber. 
Red-gum logs when left in the woods for any considerable time 
are subject to a very serious sap-rot (59) caused by the smoky Poly- 
porus (Polyporus adustus (Willd.) Fr.). The heartwood is com- 
paratively durable. Boards cut from diseased logs are very char- 
acteristic and striking in appearance. Normally, red-gum sapwood 
is a light yellowish white, commonly with a reddish tinge. The sap- 
wood in a decayed board has a number of various-colored streaks or 
lines irregularly distributed from the end of the board toward the 
middle. ‘These streaks are light orange at first, but in the more ad- 
vanced decay are a very light straw color (in fact, almost white) and 
are intermingled with lines and patches of bluish gray and the nor- 
mal-colored sapwood. Black zigzag lines may extend from the ends 
of the board for a distance of 2 inches or more parallel to the grain. 
The general consistency of sapwood with this incipient decay, which 
may extend 2 or 3 feet in advance of the typical decay, is firm and 
solid. Sapwood with the typical decay is badly broken down, being 
soft and pulpy and without firmness. 
This and other sap rots may be prevented by shortening the dry- 
ing period in the woods. Coating the ends with hot coal-tar creosote 
immediately after the logs are cut is also effective. Where possible, 
all freshly cut logs, particularly those cut during the spring and 
summer, when the rot develops best, should be peeled. Sap rots simi- 
lar to those found in the red gum are found in tupelo gum (Vyssa 
sylvatica Marsh) and in maple. 
DECAY IN FINISHED AIRPLANES. 
Little information about decay in finished airplanes is available. 
In the past there has been very small chance for airplanes to decay, 
because the completed machines rarely ever were stored, and their 
life in use was a relatively brief one; but since the conclusion of the 
World War immense quantities of airplane material have been placed 
in storage, and the average life of the machines has been materially 
increased by changes in construction. Under average conditions 
there should be practically no damage to finished airplanes by decay. 
When in use there is little danger from this source, owing to the fact 
that when not actually in flight the machines are properly housed. 
The wooden parts in the interior of the wings and around the en- 
gine are most susceptible. In these places there is an increased tem- 
perature and relative humidity. Keeping the machines in a dry 
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