PROTECTION 173 
western yellow pine I have ever seen was on a sheep 
range in Arizona, which had been judiciously grazed 
for over twenty years without a break. On the other 
hand, as complete desolation as it has ever been my 
misfortune to look upon, I have seen in the same 
region on an area once famous for the stand of grass. 
Overgrazing was the sufficient cause. Unrestricted 
sheep grazing has this single mitigating character— 
it destroys itself. The permanency of the grazing 
industry in the forest reserves depends altogether on 
its wise and effective regulation by the Govern- 
ment.” 
5. Protection against Parasitic Plants.—Forest 
trees are often seriously affected by fungus disease. 
This usually follows when the tree has been injured 
and is of low vitality. Fungus disease follows fire, 
and gains a foothold in the wounds resulting from 
wind and snow breakage. The disease starts from 
centers of infection, and gradually spreads. By the 
removal of the diseased trees from the forest this in- 
jurious influence may be reduced to a minimum. 
Various forms of cancer and witch-broom are due 
to fungus pests. In some cases these fungi have two 
host plants—that is, live part of their lives in one 
form on one species, and a part in another form on 
another species. This is so of the cedar-apple, which 
causes brown, irregularly lobed excrescences about 
