Open Access

James Herbert White

• 1. Fomes applanatus, a perennial polypore of wide distribution and of common occurrence in North America and in Europe is responsible for the decay of very large quantities of wood annually. It attacks practically all deciduous species and several coniferous species, both dead wood and living trees. This fungus, heretofore commonly regarded as a pure saprophyte, has now for the first time been comprehensively studied; the investigations recorded in this paper have followed along three main lines of inquiry; (1) a study of the morphology and the ecology of F. applanatus and of the action on its host; (2) a determination of its etiological relationships by culture methods, and a testing of the applicability of such methods to a study of the timber destroying fungi; (3) an investigation of the possibility of finding criteria by which we may distinguish parasitic action on wood from saprophytic. 2. Fomes applanatus produces basidiospores only; conidia are not produced by the mycelium, nor, as is commonly affirmed, on the upper surface of the sporophore. The basidiospores are not of the ordinary type; each consists of a yellow, papillate, thick-walled chlamydospore within a thin hyaline wall. The so-called" truncate" base is in reality the apical end of the spore. Spore discharge is enormous and continues for by far the longest period recorded for fungi. It is continuous day and night for about six months-visible from vigorous fruiting bodies as spore clouds. Discharge is not affected by variations in light, humidity of the air, or temperature within very wide limits; frost causes an instant cessation and thereafter there is no further spore fall until a new set of pores is organized. The spores were not found to retain their viability for more than 6 1/2 months. They germinate in water and various other media within 48 hours after sowing, but the percentage of viable spores is very low and their behaviour with respect to germination is erratic. 3. No difficulty was experienced in culturing F. applanatus on artificial media or on wood. Three parallel series of cultures on wood were carried through to sporulation with mycelium obtained from (a) spores, (b) pieces of sporophore, (c) pieces of diseased wood. 4. Wood rotted by F. applanatus exhibits a mottled appearance sufficiently characteristic to permit of its recognition. when compared with other rots. In the case of living wood the area of attack is delimited by a wide dark band. Histologically, the decay is characterized by a perforation and corrosion of the elements culminating in disappearance of the tissues in localized pockets into which the mycelium gathers forming strands. Chemically, the change is one of delignification followed by a progressive solution of the resultant cellulose wall except for a few resistant fragments. In the later uniform white stage of decay, the threads of F. applanatus were always found to be accompanied by other destructive agentsbacteria or fungi. 5. The particular type of decay in timber due to Fomes applanatus has now been linked with its causal agent by actual culture. 6. Fomes applanatus has been proved to be a wound parasite, and in southern Ontario at least is one of the commonest and most destructive of this type. The proof rests on three grounds: (a) the conventional test applied to other such fungi-the mycelium works upward most readily by the way of the heartwood causing a characteristic decay and outward into the sapwood, eventual1y reaching the cambium, and is apparently the cause of the death of the tissues traversed by it; (b) a broad brown band is present in the wood of living trees along the advance line of the invading mycelium of this fungus. Within this band there is a copious production of brown wound gum and an excessive multiplication of tyloses; This band steadily moves fonvard with the advancing hyphae, the tyloses and wound gum being destroyed by the mycelium along its posterior margin as rapidly as they are formed along its antedor edge. The tyloses (and possibly the wound gum alsoJ certify to the living condition of the invaded tissues; their production can be ascribed only to the influence of the fungus, and the invasion of these tissues and their fate demonstrates directly its ability to act as a parasite; (c) inoculations with the spores and mycelium of F. applanatus into living trees resulted in an extensive browning of the inoculated wood with a multiplication of tyloses-both far in excess of similar phenomena due to traumatic stimulation. 7. The occurrence of wound gum and the multiplication of tyloses in a band marking the advance of a wood~destroying fungus in a living tree would appear to furnish an unerring criterion for the recognition of the fungus as a parasite.