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Page number:43 
Description type:Non-original description 
Description:Poria nigrescens Bres. Fig. 28 Accad. Rover. Agiati Atti 3, 3:83. 1897 (S). Poria bicolor Ellis & Langl., nom. nud. in Sacc., Syll. Fung. 23:431. 1925 (non P. bicolor Bres., 1911)
Perennial, becoming widely effused, up to 15 mm thick, separable, without distinctive taste or odor; margin pale, often darkening on drying, tomentose or matted, narrow, forming progressively smaller layers and margins concentrically arranged; pore surface varying from buff to buffpink or flesh pink, sometimes darkening where bruised and frequently blackening more or less on drying, the tubes leathery to subcorky, becoming rigid on drying, in distinct layers which are each up to 4 mm thick, pores round to angular, 5-7 per mm, edges thick to thin, entire; context tan, fibrous to corky, thin, continuing without change into the trama.
Tissue not changing color in KOH; hyphal system monomitic, the context of generative hyphae which are closely compacted and form a more or less pseudoparenchymatous tissue, rarely branched, rather thin- to thick-walled, occasionally to frequently simple-septate, 5-8 p µm in diameter; tramal tissue continuous with the context and the hyphae much as in the context; hymenium 8-14 µm; thick; cystidioles occasional, 6-7 µm in diameter; basidia clavate, 8-13 x 6-8 µm; spores hyaline, smooth, IKI --, subglobose, 4-5.5 x 3-4 µm;
On angiosperms and occasionally on gymnosperms, widely distributed in Alaska, Canada and the U. S., in Cuba, Puerto Rico, Guadeloupe, Brazil, and West Java; associated with a white fibrous rot. This fungus is reported to cause decay in cooling towers, see Rev. Appl. Mycol. 37:123. 1958.
- In the first year of growth it could be confused macroscopically with Poria eupora and P. odora, but both of these have nodose-septate generative hyphae, and P. eupora has prominent cystidia. P. albostygia resembles this both externally and internally but differs in having cystidia.
P. vitrea is also similar but can be distinguished by its annual habit, -white translucent appearance when fresh, and the conspicuous pocket rot associated with it.
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