90 THE ‘‘BLUING’’ AND THE ‘‘RED ROT”’ OF THE PINE. 
development is probably very similar, although it was not possible to 
make an accurate determination of this fact because of the great 
irregularity in the rate with which infection takes place after the 
beetle attack. The rate of growth in the trunk varies considerably. 
Some trunks are invaded on all sides with equal rapidity; some, on the 
other hand, seem to be more resistant on one side or another. A good 
idea as to the presence or absence of the fungus can usually be obtained 
by observing the extent of the blue coloration, to which reference is 
made below. 
EFFECT OF ‘‘ BLUE”? FUNGUS ON THE TOUGHNESS OF THE ‘‘ BLUE” WOOD. 
On page 13 it was stated that the ‘‘blue” wood was considered 
very much tougher than the healthy wood. The tie cutters in the 
Black Hills find that it is very much harder work to cut cross-ties from 
the **black-top” wood than from green trees—so much so that they 
demand additional pay for cutting these ties. 
When split with an ax, the two halves of a block seem to hang 
together more firmly, and it requires more strength to wedge them 
apart. Chips do not fly off as easily. The only explanation which 
can be suggested for this peculiar behavior of the diseased wood is 
that in the ‘** blue” wood we have an enormous number of filaments, all 
extending radially through the wood. These filaments occur in 
bunches, much interwoven, scattered at regular intervals through the 
wood. It is estimated that at a point about 1 foot in from the bark 
there are about 39,000,000 medullary rays per square meter of tangen- 
tial surface, or about 3,700,000 per square foot. Even if the tensile 
strength of one hypha is not very great, when it comes to 4,000,000 
bundles these may have some effect in holding masses of wood fiber 
together (see Plate VIII). This view is strengthened by the fact that 
it seems easier to split the ‘‘ blue” wood along radial lines than on 
tangential lines. In making ties the tangential cut is used almost 
entirely, and it is possible that these hyphal bundles are responsible 
for the toughness. When split tangentially and viewed edgewise, one 
can see some of these hyphal bundles projecting from the medullary 
rays, as if they had been pulled out and stretched before being torn. 
RELATION OF THE ‘‘ BLUE” FUNGUS INFECTION TO THE BEETLE HOLES. 
As has been previously stated, the first evidences of the presence of 
the ‘* blue” fungus are seen some weeks after the beetles have bored 
into the cambium layer. The first signs of blue color in the wood 
might be expected just under a hole in the bark or near such a hole, 
or under the tube excavated in the bark extending from such a hole. 
This, however, is not always the case; in fact, is rarely the case. The 
small triangular patches of color may appear anywhere within the area 
