12 THE ‘‘BLUING’’ AND THE ‘'RED ROT” OF THE PINE. 
vicinity of the attack. The first signs of the blue color are found in 
the base of the trunk. On PI. VI, fig. 1, three sections of a tree which 
was attacked the latter part of July, 1901, are shown. The sections 
were cut in November, 1901, at points 5 feet, 16 feet, and 36 feet from 
the ground. The sapwood of the first section, 5 feet up, is entirely 
blued; the second section, 16 feet up, is blue here and there; while the 
section made in the top, 36 feet up, is without a particle of blue color. 
Note in this connection that the sections with blue color show the cross 
sections of the galleries of the bark beetles (Dendroctonus ponderose) in 
the layer formed by the cambium layer, the outer wood, and the inner 
bark. The sections on Pl. VI, fig. 1, show some of these galleries filled 
with sawdust. A more advanced stage is shown on Pl. VI, fig. 2. In 
this tree the sapwood is blue from the ground up into the extreme top. 
The smallest section, cut from the tree in the upper part of the crown, 
is blue with the exception of the innermost rings, 1. e., the beginning 
of the heartwood. 
The blue color develops very rapidly when once the tree is attacked. 
Standing trees attacked by the beetles in July, 1902, showed signs 
of blue color in three weeks. ‘Three months after the attack the 
sapwood of the lower part of the trunk is usually entirely blue, as 
shown on Pl. I. The year following the attack, 1. e., when the trees 
have reached the ‘‘sorrel-top” stage, the bluing has reached the top, 
and late that year, when the ‘‘red-top” stage is reached, the entire 
sapwood is blue (PI. VI, fig. 2). 
An experiment was made during the past summer to see whether 
the blue color would appear in trees felled before being attacked by the 
pine-bark beetle. It may be said at this point that they did ‘‘blue” 
just as the standing ones did. 
NATURE OF THE ‘‘ BLUE” WooD. 
Some weeks after the attack by the bark beetles, changes take place 
in the bark and the newer wood which ultimately result in the bark 
becoming loose and separating from the tree. When the first flow of 
resin into the galleries has stopped, the air enters into the galleries, and 
channels of communication with the outside are established through 
which the water in the cambium and newer wood can escape. The 
result of this is that a moist atmosphere prevails in the air chambers, 
very favorable to the growth of fungi. As the cambium and bark 
cells lose water they shrivel and break from one another, so that after 
a few months the-bark breaks away from the wood proper. On the 
south and southwest sides of the trees the bark dies most rapidly, and 
here, contrary to the general occurrence, it frequently adheres firmly 
to the tree. On the shaded sides of the trunk the bark becomes 
loosened, as described, before six months have elapsed. The surface 
of the wood is moist, very dark in color, and feels somewhat clammy. 
