The control of insect pests is a difficult matter. On areas where insect depredations are conspicuous and are liable to spread to nearby valuable timber, control measures are undertaken in coöperation with experts from the Bureau of Entomology. In these control projects, crews of men fell the infested trees, strip the bark from them, and burn the bark (usually at a time of the year when the young broods of beetles are still in the bark, namely, fall or winter). Trap trees are sometimes resorted to. In this method, trees are girdled with an ax and thereby weakened to such a degree that beetles are attracted to it. After such a tree has become thoroughly infested in this manner, it is cut down and burned. In the case of a large, conspicuous infestation, an insect reconnoissance is made, in order to obtain an estimate of the percentage of trees that have been killed by insects. When it is possible, the timber is immediately sold. For example, on the Lassen National Forest, the writer several years ago made such an estimate of an infestation caused by the mountain pine beetle, covering over 100,000 acres. The reconnoissance showed that about 35 per cent. of the trees above 12 inches in diameter had been killed. The killed timber was subsequently utilized for telephone and telegraph poles. There are many administrative measures which are practiced on the National Forests, which aim to prevent insect infestation. The prevention and suppression of forest fires, which form infection courts for insects, is probably the most important one. In all timber sales, old dead snags and slashing, which are breeding places for insects, are disposed of. Through free use and timber sales, insect-killed timber is disposed of and the loss due to insects is reduced to a minimum, besides in many cases destroying the young insect broods. _Tree Diseases._ In almost every administrative district there is a Consulting Pathologist, connected with the Bureau of Plant Pathology of the Department of Agriculture, who has charge of all work dealing with the eradication of tree diseases. A tree disease is really any condition that interferes with the normal functioning of the tree, be this condition caused by fungi, mistletoe, fumes, smoke, frost, sunscald, drought or excess of water in the soil. Parasitic fungi and mistletoes cause most of the tree diseases. Leaf diseases, by killing a greater part of the foliage, destroy the very organs in which food for the growing tissues is prepared. Diseases of the bark intercept the flow of food coming down in the bark from the leaves. Diseases of the sapwood cut off the water supply, which is pumped upward from the roots. Those that attack the roots also affect the water supply of the tree. Diseases of flowers and seeds destroy the faculty of reproduction.