SUMMARYBasidia of many Polyporaceae at the end of the rainy season and during intervals between two showers of rain have been observed to be gradually transformed into hyphal elongations with terminal spores that are exactly like basidiospores. Conversely, on the advent of rain in the middle of a dry season, the hyphal elongations soon become reconverted into regular basidia.Such conversion has been reproduced under experimental conditions. When a piece of the fruitbody of a thin and desiccated specimen was placed under the running water of a laboratory-tap overnight, the hyphal elongations entirely disappeared from the pore-tubes and the majority of the pore-tubes developed mature basidia with sterigmata and spores. When a piece of the same fruitbody was stuck to the lid of a moist agar-plate and examined daily under the microscope, it was found that, as the water of condensation gradually disappeared from the plate in the course of three or four days and the plate became comparatively dry (the relative humidity becoming reduced to about 85 per cent), the pore-tubes displayed a development of a large number of clamped and elongated hyphae with terminal spores and a few abnormal elongated narrower basidia. The experiment was repeated several times and sometimes in reverse order, and in each case the same result was obtained. Such experimental conversion was quite successful with thin and easily desiccated specimens ofPolyporus, Polystictus, andTrametes.It did not succeed well with very thick or soft specimens ofPolyporus, Trametes, Lenzites, Daedalea, Fomes, etc., as it is known that all specimens cannot withstand desiccation to the same degree. This experiment confirms my observation that it is mainly the water-relation which controls the transformation of basidia into hyphal elongations with clamp- connexions and terminal spores andvice versa.None of the previous workers (Patouillard, Matruchot, and Heim) have correlated this change of form of basidia with the varying external conditions.In some specimens ofGanoderma lucidumcollected in 1937 and 1938, brown thick-walled basidia resembling those described by Heim inPodaxis indicusandPodaxis aegyptiacusunder the name ofpseudobasidia, were found in the hymenial layer.