PROTECTION" FROM THE LOCUST BORER. 9 
Likewise, until they become 1^ to 2 inches in diameter at the base, 
trees are not subject to attack unless the bark is rough. On younger 
trees the borers are found concentrated at the base and near crotches. 
For some unknown reason trunks of trees reaching 5 to 6 inches in 
diameter and over (excepting old brood trees) rarely are found to 
contain borers. On such trees the larger branches frequently are 
infested, but such injury is seldom common enough to do much harm 
or even attract attention. It can be said, therefore, that protection 
from borer injury is necessary for only a comparatively short period 
during the tree's growth. Under good growing conditions this time 
should not exceed 10 years. 
In every locust grove that has borers present, certain trees will be 
found on which they have concentrated. These are called brood 
trees. The thick, irregularly barked, gnarled appearance and stunted 
growth will distinguish such individuals. They are often continu- 
ously infested until they reach an old age, or 12 to 18 inches in 
diameter. 
HOW TO RECOGNIZE TREES CONTAINING NO BORER DEFECTS. 
The larval mine made by the locust borer destroys a certain amount 
of the growing tissue or cambium and makes a serious defect in the 
wood. This injury to the cambium accelerates growth to heal it over 
and produces a swollen or gnarly appearance. Many such defects 
give the entire stem a roughened, distorted shape. The bark is ir- 
regular and scaly. On the other hand, trees that have not been in- 
jured by the borer are characterized by very regular bark, which is 
grooved longitudinally between thick, dark ridges. With a little 
experience these features can be quickly recognized and until the 
tree reaches 10 to 12 inches in diameter it is possible to determine 
accurately whether the borer defect will be found in the wood. 
CHARACTER OF GROWTH OF UNINFESTED STANDS. 
Not only is the appearance of uninjured individual trees charac- 
teristic but pure stands of such trees have a different appearance 
from those that are damaged. The tops of isolated natural stands 
have a domelike outline, the innermost trees growing taller and 
straighter, while root sprouts continuously coming up around the 
borders form smaller and younger trees which give additional pro- 
tection to those within. These younger trees are at first too small 
for infestation, and when they have reached a susceptible size are 
protected in their turn. The crowns are uniformly shaped and no 
branches project to break the contours. Planted stands, where the 
trees are of the same age, are uniform in height, the tops forming a 
flat outline. No large branches are found on the trunks, but many 
