26 MISC. PUBLICATION 162, U. S. DEPT. OF AGRICULTURE 
gradually grows down through it, eventually causing the death of 
the tree. As yet no practicable means of controlling the chestnut 
bark disease has been found but there is evidence that sprouts and 
other young chestnuts are developing resistance to the disease. 
Another fungous disease is the white pine blister rust which, 
strange as it may seem, lives alternately on the pine and on currant 
and gooseberry plants. The disease enters the white pines through 
the needles and grows into the bark. Diseased areas in the bark 
are called cankers. About 3 years after a tree becomes infected 
orange-yellow blisters break from the cankers. In the spring mil- 
lions of spores from these blisters are scattered by the wind over 
long distances, infecting the leaves of currant and gooseberry bushes 
The disease cannot go directly from one pine to another, but must 
first go to currants or gooseberries. It is the spores produced on the 
leaves of these plants that are dangerous to the pine trees. Since 
these spores are delicate and short lived their infecting range is 
limited to relatively short distances. Thus it is possible to control the 
disease locally by destroying currants and gooseberries in the vicinity 
of white pines. 
OTHER ENEMIES 
Animals grazing in the woods can do serious damage to both the 
mature trees and the young growth. The older trees may be injured 
by having their roots trampled and wounded and by having the soil 
around them compacted to such an extent that it is nearly impervious 
to water. Young growth is often entirely destroyed. Cattle, horses, 
sheep, and goats ‘browse young seedlings, particularly the hardwoods, 
trample them down, or brush against them and break them. Hogs 
eat the seed of certain trees and thus prevent new growth from start- 
ing. They actually root pine seedlings out of the ground and eat 
the fleshy covering of the roots. Grazing in woodlands should there- 
fore be carefully regulated if the stand is to remain productive. 
In localities where trees are shallow rooted, or the ground is soft 
because it is soaked with water, or where the trees have been weak- 
ened by fire or other agencies, srindleticimms can cause extensive dam- 
age. A bad blow down may become a fire menace, as well as a waste 
of valuable timber. 
Snow may also be very harmful, especially to young trees. It 
often loads them down, breaks, or deforms them, especially if wet 
snow falls heavily before the broadleaf trees have shed their fohage 
in the fall. In many regions, however, snow is so useful in protect- 
ing the soil and the young trees that the harm it does is offset by its 
benefits. 
FORESTRY IN THE UNITED STATES 
Wuat Forestry Is 
Forestry is the handling of forest land in such a way that it will 
raise repeated crops of timber and will exert to the fullest the bene- 
ficial influences of the healthy forest on soil and stream flow, on wild- 
life and human life. Lands that can best produce forest crops 
should be kept at work growing trees. 
