Some fungi attack living wood, some dead, and some both; and, while the majority are found growing on the stem, others attack the twigs, leaves or root. They are of all sizes, from the almost microscopical to the beefsteak fungus, which often exceeds a couple of feet in diameter. Some are jelly-like in consistency, others leathery or almost woody in texture; and while certain kinds spring up and disappear in a few days, others remain intact on the tree stem for several years. In shape, too, they vary considerably, from the curious Jew’s ear fungus, which greatly resembles the human organ, to the giant puff-ball, that sometimes measures four feet in circumference. Then the cup-shaped and parasol fungi are appropriately named, while the flat, shelf-like arrangement of a species that frequents the oak and elm has interested many a casual observer. Excepting perhaps green, they are found of almost all colours from dull brown to the brightest crimson, while beautifully spotted and mottled kinds are not uncommon. Healthy trees growing under normal conditions are little affected by fungi, whereas such as are predisposed to infection, by unsuitable soil, excessive drought or dampness, injury by accident or otherwise—in fact, those in a weakened condition however brought about—are, of course, far more liable to attacks. Though certain species of fungi only attack dead and decomposing wood, and are, therefore, the consequence and not the cause of disease, there are others, fortunately fewer in number, that attack healthy living trees and are the direct cause of disease and death. The prevention and extermination of fungus pests is by no means an easy matter, but by keeping the woods free from dead and dying trees and branches, and by giving immediate attention to outbreaks of the malady, much harm may be averted. [Illustration: LARCH CANKER] In the following notes, only the most serious cases are dealt with, or, in other words, such fungi referred to as are commonly met with and cause most damage to our woodland trees.