THE AIR SEASONING OF WESTERN SOFTWOOD LUMBER iil 
with the wood surrounding it. Depreciation from this source can 
be reduced somewhat in air seasoning by measures which prevent 
_ excessively rapid drying and extremely low final moisture content. 
BLUE STAIN > 
Blue stain does not materially affect the strength properties of 
wood. It is not an early stage of decay. It does, however, 
lower the value of the product for uses in which discolorations 
are objectionable or in which the wood is to receive a natural finish. 
In the air seasoning of western yellow pine, western white pine, 
and sugar pine, the prevention of blue stain is often the major drying 
problem. 
The blue-stain organism does not attack the living tree, and in 
wood products the blued areas are confined to the sapwood, ending 
where the heartwood begins. Apparently, conditions favorable 
for the development of the fungi are limited to sapwood stock con- 
taining a_ suitable 
amount of moisture. 
The fact that some 
species of wood blue 
more readily than 
others has not been 
explained. Possibly 
the food or moisture 
conditions in the sap 
of different woods 
vary sufficiently to 
account for this selec- 
tive action. 
Blue stain in its 
early development 
appears as spots or 
streaks. Later, asthe 
fungus penetrates 
more deeply, the en- 
tire sapwood may be ee threads (B) of a blue-stain’ fungus in se 
. pine decomposing e medullary rays a ana penetratin 
dascoloreds:)Ehede+i! the cell walls at C and D : 

fect is a discoloration 
of the stock due directly to the growth within the wood of minute 
threads of the blue-stain fungi. These fungi are very small plants 
which absorb their nourishment from the wood they inhabit, feeding 
principally upon the cell contents. As the fungus threads grow, they 
pass from one cell to another, usually through the thin parts of the 
cell wall but occasionally boring through the wood fiber. The blue- 
gray color appears only after these numerous small threads have 
reached a certain stage of development within the wood cells. (Figs. 
2 and 3.) 
Later on, when these threads feeding on the contents of the cell 
and to a slight extent on the cell walls have developed further, fruit- 
ing bodies comparable in some ways to the flowering part of a green 
5 Acknowledgment is made by the authors to E. E. Hubert, formerly assistant patholo- 
gist, Bureau of Plant Industry, who has contributed so materially to the present knowledge 
of the blue-stain fungi, for the material presented in this section, i 
