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- 

 erosde) 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 (PL 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 of a 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 



