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While preparing a monograph on the genus Clitocybe Kummer in Fennoscandia I have become acquainted with a phenomenon called hygrophany. In connection with pure taxonomical studies I have had to pay special attention to it and will in the following make some contribution to the knowledge of this phenomenon. The genus Clitocybe is very suitable for studying hygrophany because it includes both hygrophanous and non-hygrophanous species as well as some intermediate types. The term hygrophanous was probably coined by E. Fries who used it for the first time in 1836 in his «Epicrisis« e.g. in the division of the tribus Clitocybe and the genus Cortinarius. Since his time the term has been well established in mycological literature. It is remarkable, however, that the literature records no attempts to search for the reasons why «the cap gets darker when water-soaked and fades beginning from the centre when drying« as one is usually advised when consulting a mycological hand-book. However, some researches have been made on the water economy of fleshy fungi, especially that of PIESCHEL ( 1924) , in connection with which some aspects of the phenomenon have been dealt with. When studying hygrophany I have examined the anatomy of the fruit-body and studied macroscopically the soaking and transpiration of water of various parts of the basidiocarp, both in whole fruit-bodies and in parts removed from them. My definition of hygrophany (in a broad sense) is very simple and is but slightly modified from that of LoHWAG (1941 [1965]): Fungal tissue is hygrophanous when it gets darker when absorbing capillary water into intercellular spaces, and paler again when the intercellular water gets transpired and the intercellular spaces gft filled with air. Accordingly, a necessary qualification for the tissue to be hygrophanous is that it be spongy and thus be able to absorb water by capillary attraction into the intercellular spaces and to transpire that «extra« water more or less easily. PrESCHEL (op.c.), whose studies seem to have included at least one hygrophanous species of Clito•cybe, has shown that the method of water uptake described above is by no means restricted to hygrophanous species. The fruit-bodies of the latter seem, however, to be able to bind more extrahyphal water than those of non-hygrophanous species. Accordingly, the tissue does not immediately darken ( = be hygrophanous when absorbing capillary water, but the amount of water must apparently be rather great for the colour change to be observable. Physiologically, the distinction between hygrophanous and nonhygrophanous tissues is thus not very precise. For taxonomical purposes it is, however, rather practical and valuable. In my definition I have used the word «tissue« because I have found that the waterabsorbing abilities of different parts of the fruit-body are different, and they accordingly must be dealt with separately. Hygrophanous tissues are very common in fungal fruit-bodies among Basidiomycetes as well as Ascomycetes, not excluding •the thalli of Lichenes. In Clitocybe the cortex of the stipe, the lowermost tramal layer of the cap, the cutis

On hygrophany of the basidiocarp in the genus Clitocybe Kummer