Page:Popular Science Monthly Volume 29.djvu/626

608 pores, just visible to the eye in some species (see Fig. 6 in August number), from ten to twelve thousand occurring per square inch; others are coarser and not so numerous. Minute as are these pores, their interior is studded with the basidia and spores, a few of which, magnified four hundred diameters, are shown in Fig. 15, where a represents sterile cells and b the basidia, usually having four sterigma, each of them bearing a spore.

Fig. 14 represents a very interesting but destructive type of fungi, and, in one sense of the word, parasitic upon living trees. It is drawn from Polyporus fomentarius (Fr.), "Dingy-hoof Polyporus." Pileus ungulate, sometimes four to five inches broad, sub-triangular, obsoletely zoned, nodulose, brownish-gray, resembling coffee slightly tinged with milk; its peculiar form and color make it easily identified. Closely allied to it are Polyporus nigricans (Fr.), Black-hoof Polyporus; pileus pulvinate; Polyporus igniarius (Fr.), Rusty-hoof Polyporus; pileus at first tuberculoso-globose (immarginate); Polyporus fulvus (Fr.), Tawny-hoof Polyporus.

The first three are found upon beeches, willows, hornbeams, cotton-woods, and plums, and trees of similar characteristics, and grow upon live trees, where they have been injured by the breaking of limbs, or by the checking of other limbs, at the junction with the trunk of the tree. Polyporus fulvus (Fr.) is found upon the firs. The mycelia,



once started, will continue to grow in the heart-wood of the tree, while the sap-wood, with its bark, is still growing. If the wound is not closed by the growing tissue, the decay continues, causing hollows in the trees. These are not uncommon sights to those familiar with forests, and the trees almost seem to be conscious that they must keep their bark intact, or the invisible fungi will start and eventually destroy their stately proportions.