﻿40 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 



summer wood is scarcely affected. In this condition the wood sep- 

 arate*, readily along the annual rings. 



Hard/wood Jogs and lumber. — Certain fungi (Polystictus versi- 

 color (L.) Fr v St( n inn Mrmtwn (Willd.) Pers., and others) cause a 

 sap rot very difficult of detection in its incipient stage. The typical 

 decay is very light 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 (Poly poms 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 gimi (Nyssa 

 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. 

 AYhen 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 humidit} 7 . Keeping the machines in a dry 



