Ewe 
THE ‘‘BLUE’’ WOOD. 11 
WHEN ARE THE TREES DEAD/ 
The question as to when a tree is dead is one of considerable prac- 
tical importance in determining which trees in the forest should be 
cut. For this purpose it is safe to assume that a tree may be pro- 
nounced dead when the bark is loose at the base of the tree for con- 
siderable distances up the trunk. A tree with its bark in this condi- 
tion can not possibly recover. The wood under this loose bark will 
always be found to be dark in color and will appear covered with 
shreds of bark when the bark is pulled off. It must be remembered 
that such trees will have green leaves. The criterion of green or yel- 
low leaves is not a safe one to follow, and ought not to be considered 
in making specifications for cutting dead timber. Attention is here 
called to the recommendation (4) made on page 35. 
THE ‘**‘BLUE” WOOD. 
Very soor after the attack of the bark beetles (Dendroctonus pond- 
erose) the wood of the pine turns blue. The color at first ‘is very 
faint, but it soon becomes deeper. A cross section of a trunk several 
months after the beetle attack will appear much as shown on Pl. V, 
fig. 1. Lines of color extend in from the bark toward the center of 
the tree, and increase rapidly in intensity until the colored areas stand 
in sharp contrast to the unaffected parts. The color appears in small 
patches at one or more points on the circumference of the wood ring. 
At first it is a mere speck, but this gradually spreads laterally and 
inward, eventually forming triangular patches on cross section. The 
color likewise spreads up and down the trunk from the central spot. 
As the time passes after the first attack of the beetles, several color 
patches may fuse. Their progress laterally and upward toward the cen- 
ter of the trunk may be equally rapid on all sides of the tree, or more 
rapid on one side than on another (PI1.V, fig. 2). The intensity of the 
color may vary considerably on the two sides of one and the same trunk. 
After a certain period of time the whole sapwood will have a beautiful 
light blue-gray color, as shown on Pl. I. The wood which adjoins the 
inner line of the **blue” wood is of a brilliant yellow color, which con- 
trasts sharply with the blue outside and the straw yellow of the heart- 
wood. This yellow area is in the form ofa ring of more or less irregular 
shape. Sometimes it is formed of one annual ring very sharply 
defined; then, again, it may include all or only parts of several annual 
rings. As the wood grows older, the blue color becomes deeper and 
the yellow ring more sharply defined. 
RATE OF GROWTH OF THE BLUE COLOR. 
The first signs of the blue color are usually found several weeks after 
the attack by the beetles at points on the trunk in the immediate 
