To mention one or two additional forms, Trametes Pini is common on pines, but, unlike its truly parasitic ally, Tr. radiciperda, which attacks sound roots, it is a wound parasite, and seems able to gain access to the timber only if the spores germinate on exposed surfaces.  The disease it produces is very like that caused by its ally; probably none but an expert could distinguish between them, though the differences are clear when the histology is understood.

Polyporus fulvus is remarkable because its hyphae destroy the middle lamella, and thus isolate the tracheides in the timber of firs; Polyporus borealis also produces disease in the timber of standing conifers; Polyporus igniarius is one of the commonest parasites on trees such as the oak, etc., and produces in them a disease not unlike that due to the last form mentioned; Polyporus dryadeus also destroys oaks, and is again remarkable because its hyphae destroy the middle lamella.

With reference to the two fungi last mentioned I cannot avoid describing a specimen in the Museum of Forest Botany in Munich, since it seems to have a possible bearing on a very important question of biology, viz., the action of soluble ferments.

It has already been stated that some of these tree-killing fungi excrete ferments which attack and dissolve starch grains, and it is well known that starch grains are stored up in the cells of the medullary rays found in timber.  Now, Polyporus dryadeus and P. igniarius are such fungi; their hyphae excrete a ferment which completely destroys the starch grains in the cells of the medullary rays of the oak, a tree very apt to be attacked by these two parasites, though P. igniarius, at any rate, attacks many other dicotyledonous trees as well.  It occasionally happens that an oak is attacked by both of these polyporei, and their mycelia become intermingled in the timber; when this is the case, the starch grains remain intact in those cells which are invaded simultaneously by the hyphae of both fungi.  Prof.  Hartig lately showed me longitudinal radial sections of oak timber thus attacked, and the medullary rays showed up as glistening white plates.  These plates consist of nearly pure starch; the hyphae have destroyed the cell walls, but left the starch intact.  It is easy to suggest that the two ferments acting together exert (with respect to the starch) a sort of inhibitory action one on the other; but it is also obvious that this is not the ultimate explanation, and one feels that the matter deserves investigation.