Abstract
1. The present paper deals with the results of the writers' investigations on the relative resistance of beech wood (Fagus crenata BL.) to sixteen species of wood-destroying fungi under controlled laboratory conditions.
2. It is advisable to adopt HUBERT's suggestion that the length of service of wood with respect to decay should be termed decay durability and the relative resistance of wood to decay under controlled laboratory conditions should be termed decay resistance. The results of the writers' experiment will be effectual in order to get an approximation of the relative durability of the wood, though they do not tell absolute durability.
3. In the experiment, the fungi to be tested had been previously grown on an agar medium in the flasks of a special shape, before the test blocks of beech wood were inserted and then kept, as they scand, at 24°C for 320 days long.
4. The fungi tested are as follows: Polystictus hirsutus, P: sanguineus, Polyporus rhodophaeus, P. orientalis, P. Patouillardii, P. Mikadoi, P. Schweinitzii, P. betulinus, P. sulphureus, Ganoderma applanatum, G. lucidum, Irpex consors, Stereum frustulosum, S. induratum, Fomes pinicola and Trametes Dickinsii.
5. The mycelia of Polyporus Mikadoi, P. orientalis, P. Patouillardii, Ganoderma applanatum and G. lucidum indicated clearly the formation of zone-lines in the places of contact with the glass-walls of the flasks.
6. In the present experiment the test blocks infested with Polyporus Mikadoi showed the most serious decay and those infested with Stereum frustulosum showed the highest resistance. Losses in average dry weight of the blocks were 60.92% in the former and 11.15% in the latter.
7. The degree of losses in dry weight of the test blocks did not run parallel with the grade of the mycelial growth on them. With an exception of Polyporus Mikadoi, the fungi which cause white pockets in woods showed generally a tendency of the poor growth of mycelium and a little loss in dry weight of the beech wood. But they produced clear pockets in the deep portion in the blocks.
8. In the case of Polystictus hirsutus and P. sanguineus, in which the optimum temperatures for their mycelial growth are conspicuously higher than the temperature used in the experiment, the superficial portion of the test blocks decayed highly and consequently the fairly high percentages of the weight-loss were recorded. However, the almost sound tissue of the wood remained in the central portion.
9. Polyporus orientalis and P. Schweinitzii, which are commonly found on pine-trees and other conifers in Japan, caused the rot of the test blocks in the experimental conditions, the former showing white pockets and the latter brown cubical rot.
