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The Formosan form of the Japanese Cypress (Chamaecyparis obtusa S. et Z. f formosana-HAYATA) occurring in the primeval forests of Formosa would be of considerable importance as a valuable timber tree and would commaind a high price, if it were not so frequently affected by brown rot in the heartwood. The cause of this rot has not been thoroughly studied so far. According to the authors' investigations the causal fungus belongs to the section Veluticeps of the genus Hymenochaete, and is closely related to, though not identical with, Veluticeps fusca HUMPH. et LONG It attacks chiefly the heartwood of the trunks, branches and roots of the living trees. A cross section of the affected trunk usually shows several, or many, light brown lesions scattered in the heartwood. They are of irregularly roundish or oblong outline, extending with their longer axis along the annual ring, and measur 2-35 cm in length, 1-20 cm in width, but may become larger with age by mutual coalescence. At the same time their colour gradually darkens into chestnut-brown. In a still more advanced stage these lesions are broken up into cuboid masses on drying through the shrinkage cracks that extend either radially or following the annual rings, and the affected part of the wood is easily crumbled into fine dust. The fruiting bodies of the fungus are found as well on the outside of broken branches, as inside the hollows produced by the rot in the wood of broken branches in some cases also on the exposed wood of the trunks, where the bark has been ripped off. They are resupinate, effused on the surface of the wood, of roundish or irregular shape, corky, becoming rigid on dryjng, and measure 1-12 cm in length, 0.7-7 cm in width. Their margins are free or slightly reflexed, the reflexed parts being at first villous, but becoming rough at last. They are concentrically sulcate, and exhibit a dark brown or blackish colour. The hymenial surface is plane, velutinous, at first light brown, later olivaceous brown to rusty brown, fading with age, finally turning to drab, and is densely studded with protruding fascicles of brownish hyphae resembling cystidia. These hyphae are irregularly branced, hyaline or colored, often distinctly nocloso-septate, 3-5μ in diam. The basidia are long-clavate, 50-130μ in length, 6.5-8.5μ in width, with slender conspicuous sterigmata 6-10μ long. The basidiospores are elliptical or elongate-elliptical, flattened on one side, hyaline or rarely of dilute olivaceous colour, 10-19μ (mostly 11-13μ) in length, 3.5-5μ in width. The fungus gorows as well on various plant decoctionagar as on CZAPEK's agar. Among these media onion agar, prune agar, potato-dextrose agar, malt agar and soy agar give favourable results. A study has also been made regarding the influence of temperature on the mcelial groowth. For this purpose theauthors used onion and prune agar media in plate incubated at various temperatures, namely, 10° 16° 19° 22° 25°28°and 31℃. From these experiments it is found that the optimal temperature for the mycelial growth of this fungus lies between 19° and 25℃., in all probability at 22℃. or thereabout, while the maximum comes near 31℃ and them minimum seems to extend somewhat below 10℃.
日本植物病理学会の論文
1936-03-30

扁柏の抹香腐に就て

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