Of the shelf fungi, which project like brackets from the stems of trees, and have their pores on their under surfaces, one of the commonest in many localities is the yellow cheese-like Polyporus sulphureus, Fig. 83. This is found on oak, poplar, willow, larch, and other standing timber.
Its spawnlike threads spread from any exposed portion of cambium into the pith-rays and between the annual rings, forming thick layers of yellowish-white felt, and penetrating the vessels of the wood, which thereupon becomes a deep brown color and decays.
Of the umbrella-shaped gill-bearing fungi, a yellow toadstool, called the honey mushroom (Agaricus melleus), is a good example, Fig. 84.
Fig. 84. Honey Mushroom. Agaricus melleus. 1. Cluster of small sporophores. 2. Larger sporophore with root-like organ of attachment. Forestry Bulletin 22. Plate XII, Figs. 1 and 2.
This fungus, of common occurrence in the United States as well as in Europe, is exceedingly destructive to coniferous trees, the white pine in particular suffering greatly from its attacks. It also fastens upon various deciduous species as a parasite, attacking living trees of all ages, but living as well upon dead roots and stumps and on wood that has been cut and worked up, occurring frequently on bridges, railroad ties, and the like, and causing prompt decay wherever it has effected an entrance. The most conspicuous part of the fungus is found frequently in the summer and fall on the diseased parts of the tree or timber infested by it. It is one of the common toadstools, this particular species being recognized by its yellowish color, gills extending downward upon the stem, which is encircled a little lower down by a ring, and by its habit of growing in tufts or little clumps of several or many individuals together. It is also particularly distinguished by the formation of slender, dark-colored strings, consisting of compact mycelium, from which the fruiting parts just described arise. These hard root-like strings (called rhizomorphs) extend along just beneath the surface of the ground, often a distance of several feet, and penetrate the roots of sound trees. By carefully removing the bark from a root thus invaded the fungus is seen in the form of a dense, nearly white, mass of mycelium, which, as the parts around decay, gradually produces again the rhizomorphs already described. These rhizomorphs are a characteristic part of the fungus. Occurring both in the decayed wood from which they spread to the adjacent parts, and extending in the soil from root to root, they constitute a most effective agency in the extension of the disease. * * *
External symptoms, to be observed especially in young specimens recently attacked, consist in a change of the leaves to a pale sickly color and often the production of short stunted shoots. A still more marked symptom is the formation of great quantities of resin, which flow downward thru the injured parts and out into the ground. (Forestry Bulletin No. 22, p. 51.)
Of the irregular shaped fungi, one of the most destructive is a true parasite, i.e., one that finds lodgment without help, called Polyporus annosus and also Trametes radiciperda, Fig. 85. It is peculiar in developing its fructifications on the exterior of roots, beneath the soil. Its pores appear on the upper side of the fructifications. It attacks only conifers.
Its spores, which can be readily conveyed in the fur of mice or other burrowing animals, germinate in the moisture around the roots: the fine threads of "spawn" penetrate the cortex, and spread thru and destroy the cambium, extending in thin, flat, fan-like, white, silky bands, and, here and there, bursting thru the cortex in white, oval cushions, on which the subterranean fructifications are produced. Each of these is a yellowish-white, felt-like mass, with its outer surface covered with crowded minute tubes or "pores" in which the spores are produced. The wood attacked by this fungus first becomes rosy or purple, then turns yellowish, and then exhibits minute black dots, which surround themselves with extending soft white patches. (Boulger, p. 73.)
Fig. 85. 1. Stump of Norway Spruce, with a sporophore of polyporus annosus several years old; the inner portions of the stump wholly decayed.