The recent ravages of the chestnut-tree blight and the appalling depredations of the gypsy and brown-tailed moths, together with other evils, suggest at once the bigness of these problems and the importance of their study and solution. The insect army is as innumerable as the leaves in the forest. This army occupies points of vantage in every part of the tree zone, has an insatiable appetite, is eternally vigilant for invasion, and is eager to multiply. It maintains incessant warfare against the forest, and every tree that matures must run a gantlet of enemies in series, each species of which is armed with weapons long specialized for the tree's destruction. Some trees escape unscarred, though countless numbers are killed and multitudes maimed, which for a time live almost useless lives, ever ready to spread insects and disease among the healthy trees. Every part of the tree suffers; even its roots are cut to pieces and consumed. Caterpillars, grubs, and beetles specialize on defoliation and feed upon the leaves, the lungs of the trees. The partial defoliation of the tree is devitalizing, and the loss of all its leaves commonly kills it. Not only is the tree itself attacked but also its efforts toward reproduction. The dainty bloom is food for a number of insect beasts, while the seed is fed upon and made an egg-depository by other enemies. Weevils, blight, gall, ants, aphids, and lice prey upon it. The seed drops upon the earth into another army that is hungry and waiting to devour it. The moment it sprouts it is gnawed, stung, bitten, and bored by ever-active fiends. Many forest trees are scarred in the base by ground fires. These trees are entered by insects through the scars and become sources of rot and insect infection. Although these trees may for a time live on, it is with a rotten heart or as a mere hollow shell. A forest fire that sweeps raging through the tree-tops has a very different effect: the twigs and bark are burned off and the pitches are boiled through the exterior of the trunk and the wood fortified against all sources of decay. This preservative treatment often gives long endurance to fire-killed timber, especially when the trees killed are yellow pine or Douglas spruce. Many a night in the Rocky Mountains my eager, blazing camp-fire was burning timber that forest fires had killed forty and even sixty years before.