Order 5. Polyporaceæ (Pore-Fungi). An order very rich in species (about 2000 species are described). The fruit-body is of very different forms—resupinate, projecting like a bracket, hoof-like, or umbrella-shaped. In some it is fleshy and edible, in others leathery or corky, persisting for several years. The hymenophore is situated on the under side of the fruit-body, and consists of wide or narrow tubes or pores, whose inner surface is clothed with the hymenium (Fig. [167]). In some fruit-bodies large cavities are to be found, which have arisen as interstices between the labyrinthine curved and reticulate folds. Chlamydospores are known in some species. Conidia occur very rarely. Many species work considerable damage: some as parasites on trees, others by destroying timber.
Fig. 167.—Polyporus igniarius. Section through the under side of the Fungus: h-h is hyphal-tissue between the tubes, formed by irregularly felted hyphæ, many of which are seen cut across; s is the hymenium which covers the walls of the tubes, and from which the basidia with the spores protrude.
Genera. Polyporus (Pore-Fungus). The tubes are narrow, accurately fitted together, and forming a thick layer on the under side of the fruit-body, appearing as a number of fine holes. The fruit-body most frequently resembles a bracket, or is hoof-shaped, with one side growing from a tree-trunk; it is very often perennial, and a new layer of tubes arises in each succeeding period of vegetation. Strata, corresponding to the periodically interrupted growth, are thus formed in storeys one above the other, and are visible on the upper surface of the fruit-body, as well as in the interior, as a series of concentric belts, sometimes as many as half a score or more in number. P. fomentarius (Touchwood) attacks trees, especially the Beech. The spores germinate on wounds from broken branches, and the hyphæ, following the course of the medullary rays, find their way into the interior of the tree, from whence the mycelium spreads upwards, downwards, and peripherally, so that the wood becomes rotten (“white-rot”) and thick felts of mycelium are formed in radial and tangential directions. A dark line, caused by the youngest parts of the hyphæ containing a brown juice, marks the boundary between the rotten and the unattacked parts of the stem (Fig. [168]); at places where the mycelium extends to the bark, the cambium becomes destroyed and further growth is arrested, so that longitudinal furrows arise on the stem. It is at these places, too, that the hoof-shaped, ash-coloured fruit-bodies are developed, which may attain a circumference of upwards of 7 feet. The interior of the fruit-body consists of a dried-up, loosely felted, red-brown mass of hyphæ, which has been used for tinder and as a styptic (“Fungus chirurgorum”). P. igniarius has a harder, dark-brown, more rounded fruit-body; it grows in a similar manner, but especially attacks Oaks, Poplars, and Plum-trees, the wood of which becomes rotten, and is called touchwood. P. pini (Trametes pini), (Fig. [170]), a parasite on the stems of Pinus, causes a kind of “red-rot” in the stem. P. sulphureus has a soft, cheesy, yellow fruit-body; it produces “rot” in Oaks and Apple-trees. P. officinalis, Larch-fungus (“Fungus Laricis” in Pharmocopœia), grows on Larch-trees in the south-east of Europe. P. versicolor has thin, semicircular fruit-bodies, with zones of various colours on the upper side; it is one of the most frequent species on tree-stems. P. frondosus grows on soil in woods, and consists of numerous aggregated fruit-bodies, which become very large and fleshy. This species is edible. P. perennis also grows on the soil in woods; it is very leathery, with central stalk, and has concentric zones on the upper surface of the fruit-body. P. vaporarius destroys the wood of living Pines (Pinus silvestris) and Firs (Picea excelsa), causing it to become red-brown; in timber this Fungus causes “red-strip” followed by a “dry-rot.” P. squamosus destroys many Walnut-trees, and is also very destructive to Limes and Elms. P. fulvus causes a “white-rot” in Abies alba.
Fig. 168.—Section of stem of a Beech attacked by P. fomentarius: a non-attacked parts of the stem; b the furrows where the mycelium has reached the bark, and where the thick mycelium-strands reach the exterior (⅙th of the nat. size).
Fig. 169.—Base of a Fir-tree, with a number of fruit-bodies of Heterobasidion annosum just beneath the surface of the soil, indicated by the dotted line (¼th nat. size).
Fig. 170.—A fully developed fruit-body of Polyporus pini (Trametes pini), lateral view (nat. size).