Luminescent wood, collected at various localities in the Netherlands, always contained Armillaria mellea as the luminescent organism (§ 2). Collecting luminescent leaves, we once found sporophores of a small Mycena, closely answering the diagnosis of M. capillaris, on the luminescent spot. Unfortunately, the spores have not germinated (at 230 C.). M. capillaris was cultivated later on from spores, applying lower temperatures: these cultures on cherry- and bread-agar were non-luminescent. Therefore, and for small morphological differences, some doubt exists as to the full identity of the fungus, causing the luminescent spots, with M. capillaris, but it may well be deemed very probable that the special, small Mycena, pictured in fig. 1 of Plate I, is the cause of the luminescent spots on beech- and oakleaves (§3). A detailed discussion is devoted to data found in the literature concerning the distribution of luminescence in fungi, and to the taxonomical value of the various luminescent species. The principal data, forming the basis of this discussion, have been collected in Tables I and II, the outcome of the discussion has been summarized in Table III (p. 188—191). In the latter Table a discrimination between the various species has been attempted, according to their taxonomical meaning, the reliability of the records of their luminescence, and the profoundness of the knowledge existing concerning them. Indications as to species which specially deserve renewed attention, and a few directions for making observations along this line are given (§ 4). Sending of material and informations will be welcome. In order to select luminescent fungi, suited for physiological wrork, as many species as possible were grown in pure culture on cherryand on bread-agar. Some characteristics of the cultures are described (§5). As a rule the brightest luminescence was observed in Armillaria mellea, Mycena polygramma, and Omphalia flavida. Mostly, luminescence was stronger on bread-agar than on cherry-agar.