PSATHYRELLA DISSEMINATA 53 



of the term cystidiujii and define it as meaning any hair-like cell 

 which is not a hasidimn or a paraphysis and which freely projects 

 from the cell-layer that covers the top of the pileus, the sides or edges of 

 the gills, or the stipe. Then we could speak of such hairs as occur 

 on the top of the pileus of Psathyrella disseminata as pilocystidia 

 (Fig. 27, A and B, p. 46), of such hairs as occur on the gill-edges 

 as cheilocystidia (E), and of such as occur on the stipe as caulo- 

 cystidia (D). In Psathyrella disseminata, as it happens, there are 

 no cystidia on the sides of the gills ; but, if there were, we could call 

 them pleurocystidia. This nomenclature can be used generally for 

 Agaricineae, and has the advantage of retaining the old term 

 cystidium which has now been used in connection with the gills for 

 nearly one hundred years. The prefixes are topographical only. 

 The use of these terms might save words in systematic descriptions 

 and introduce into them a little greater precision. 



A still better set of terms, if the history of mycological nomen- 

 clature did not exist, would be pilotrichome, j^leurotrichoine, cheilo- 

 trichome, and caulotrichome ; but if they were to be adopted the 

 term cystidium, which has become engrained in the literature of the 

 Hymenomycetes, would be drojDped. Doubtless, few mycologists 

 would be wilHng to start de novo in this way. The best compromise 

 therefore seems to me to be the accejitance of the terms pilocystidium, 

 cheilocystidium, pleurocystidium and caulocystidium. 



Correlation of Facts. — The fruit-body of Psathyrella disseminata 

 is organised for a very ephemeral existence only. Its spore-dis- 

 charge period, as we have seen, is not longer than about 18 hours. 

 The stipe is very slender, hollow, and weak ; and the pileus is very 

 delicate. The pileus-flesh is well-developed only at the disc ; 

 elsewhere, it is extremely thin and becomes split up into radial 

 ribbons during the expansion of the pileus. The gills are very thin 

 and become partially split down their median planes : they are 

 evidently too frail to function for any long period. In the general 

 softness of its mechanical structure and in its extremely limited 

 power of resisting loss of water by transpiration, the fruit-body of 

 Psathyrella disseminata resembles the fruit-bodies of many small and 

 very ephemeral Coprini such as Coprinus ejihemerus. 



Correlated with the very short spore-discharge period, the number 



