12 DEPARTMENT BULLETIN 1425, U.S. DEPT. OF AGRICULTURE 
plant are produced upon the surface of the wood. (Fig. 4.) These 
fruiting bodies, resembling small black hairs or bristles swollen at 
the base, A, appear as tiny black specks upon the blued wood. From 
them, minute spores, B, are ejected which, when carried about by the 
wind or other means, cause new infections by germinating on bright 
lumber green from the saw or on other favorable places. 
Although the blue-stain organism may be present in certain logs 
before these are sawed into lumber, the chief source of infection is 
the fresh spores. Accordingly yard sanitation, including avoidance 
of the too frequent use of crossers, is highly important in blue-stain 
prevention. 
The conditions for rapid development of blue stain are essentially 
the same as for the development of true wood-destroying fungi. Both 
require an abundant food supply, a comparatively high moisture con- 
tent of the wood, and warm weather. Staining 1s always severe dur- 
ing rainy periods in the warmer seasons of the year when the air 1s 
humid and seasoning is corre- 
spondingly slow. Under such 
conditions, if proper piling and 
storage methods are not em- 
ployed, very heavy staining 
may occur, particularly in 
fresh-cut stock. 
It has been observed that 
these fungi grow best on sub- 
stances which contain some 
acid, the acid of sour sap being 
very favorable for the develop- 
ment of the blue-stain organ- 
ism. This explains why “ sour- 
ing” or “fermenting” of the 
sapwood is een as 
at the origin of the blue-stain 
ance ood Wee cr Wien katie wanes Hiemich ae than the true 
the direct penetration of the cell walls. In 
the lower center one thread is passing cause, fungus development. 

through a bordered pit. It is the presence 4 1 1 j 
of such threads within the cells that gives From the Investigative work 
the blue color to the wood on the moisture requirements 
of the blue-stain organism 
thus far attempted, it seems safe to assume that there is little danger 
of sap-stain development in wood with a moisture content of 20 per 
cent or lower. In air seasoning the occurrence of this defect is 
primarily the result of insanitary yard conditions and slow drying. 
Preventive measures include sanitation and yard practice which will 
permit rapid drying, especially in the initial stages and in the lower 
third of the lumber pile. 
Blue stain is the only stain of economic importance in the air sea- 
soning of western softwood lumber and is a major problem only in 
drying the pines. In view of the general climatic conditions and the 
usual drying periods required in the West, decay need not be con- 
sidered as an air-seasoning defect. Of course, incipient infections of 
decay that may cause trouble with the stock in later use should be 
guarded against, but any of the measures taken to reduce blue-stain 
development are also helpful in preventing decay. 
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