1 6 RESEARCHES OX FrXGT essential function of producing spores. Instances of sterility ot this kind have been noticed in two different species. A board was found in a cellar infected with Coprinus fimetarius, var. cinereus, and a small piece of it, bearing a young fruit-body, was sawn off, brought to the laboratory, and placed in a danip-chainber. After further development the fruit-body attained average size and form, but exhibited the peculiarity of being yellowish-white in colour instead of ashy grey. Upon examining the pileus with the microscope, I found that it was almost completely sterile. Only a few basidia had produced spores, whilst the great majority had remained in a rudimentary condition. The normal basidia were found chiefly at the pileus margin, but a very few Avere sparsely scattered over the general surfaces of the gills. Two other fruit-bodies subsequently appeared on the piece of board, but in these the spores were developed in the usual manner. Coprinus plicaiiloides'^A vas grown on sterilised horse-dung, from the surface of which its fruit-bodies Avere produced in large numbers, several each day for more than a month. At successive intervals about six fruit-bodies came up, Avhich seemed to be quite normal in size and form, but which Avere conspicuous among their companions by being Avhitish-yelloAV instead of grey. The microscope revealed the fact that the gills had failed to produce any spores. The basidia, surrounded by large paraphyses, had remained quite small ; they did not protrude beyond the general surface of the hymenium and, so far as I could observe, they had not even given rise to sterigmata. The cause of the occasional sterility of Coprinus fruit-bodies seems to be somcAvhat obscure. Since, however, the sterile fruit-bodies of Coprinus j)licatiloides grew in company Avith, and closely adjacent to, other fruit-bodies which Avere completely fertile, it seems safe to infer that the sterility was not conditioned by temperature, light, heat, moisture, or atmospheric gases. Perhaps the phenomenon is due to some accident happening to the mycelium at the time Avhen its contents are being poured into the young fruit-body. It is conceivable that, if the mycelium attached to the fruit-body were reduced in quantity, the fruit-body might suffer from starvation during its further development, and yet, in consequence of thê For iKJineiiclaturu of this species, ri,h infru, Cluxp. IV.

RESEARCHES ON FUNGI cystidia (metuloids), which are very numerous, prominent, and encrusted with calcium oxalate, could not possibly act as spacing agents ; for here the hymenium is smooth. Possibly, in this genus, they serve to protect the fruit-bodies from slugs or other harmful animal parasites. The same interpretation might apply to the rigid coloured seta? of Hymenocha^te, but does not seem suitable for those of some species of the woody genus Fomes, e.g. F. nigricans and F. salicinus. De Bary's J investigation led him to the conclusion that in Lactarius delieiosus the cystidia arise from ordinary hyphre of the trama, but according to Massee 2 the cystidia of Russula and Lactarius are direct terminations of the laticiferous system. Massee's view is supported by the Avork of BifTen, 3 who found that in Collybia velutipes the cystidia form the hymenial endings of the conducting hyprne. In these cases, doubtless, the cell contents are of importance, although exactly in what way still remains to be explained. In Russula, at least, they do not seem to render the gills unpalatable to slugs, since these animals are particularly fond of the members of this genus, and often devastate the fruitbodies in a wood to such an extent that scarcely a single specimen is left undamaged. Earlier writers, Corda and others, stated that the cystidia of the fleshy fungi discharge their contents through their apices in the form of drops, but de Bary 4 and Brefeld could never satisfy themselves that this is done spontaneously. However, Massee and Worthington Smith have both upheld the older view. According to Massee, 5 cystidia, when mature, contain glycogen which is emitted through the nipple-like openings at their apices, and poured over the surrounding hymenium, where it serves as food for the developing spores. Smith 6 has figured the cystidia of Coprinus atramentarius, Gomphidius viscosus, and Agaricus radicatus as large, tiask-like 1

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The Hymenium Basidia and Paraphyses Nuclear phenomena The Colour of Spores Two-spored Basidia in Cultivated Varieties of Psalliota campestris Occasional Sterility of Coprinus Fruit-bodies Cystidia Fungus Gnats, Springtails, and Mites Position of the Hymenium Comparison of the Basidium with the Ascus The Effect of Sunlight upon Spores. 6 CHAPTER II The Extent of the Hymenium Principles underlying the Arrangement of Gills and Hymenial Tubes The Margin of Safety The genus Fomes. 27 CHAPTER III The Functions of the Stipe and Flesh of the Pileus The Gill-chamber. 39 CHAPTER IV Adjustments of Fruit-bodies in the Interests of Spore-liberation Lentinus lepideus, Psalliota campestris, Polyporus squamosus, Coprinus plicatilis, ('oprinus niveus, and Coprinus plicatiloides Reactions of Fruit-bodies to Light and Gravity The Problem of Pileus Eccentricity Geotropic Swinging Rudimentary Fruit-bodies 47 CHAPTER V Spore-deposits The Number of Spores 79 CHAPTER VI Macroscopic Observations on the Fall of Spores of Polyporus squamosus. .