PSATHYRELLA DISSEMINATA 49 



the hymenium produces and liberates spores at the same time. It 

 is evident, therefore, that Psathyrella disseminata belongs to the 

 Aequi-hymeniiferous Type. However, I have not yet tested the 

 gills by experiment to find out whether or not they follow the usual 

 rule and are positively geotropic : it is just possible that they are 

 non-geotropic like those of the Copfini. The gills are developed 

 radially in the young fruit-body. The stipe is strongly negatively 

 geotropic and, just before spore-discharge is about to begin, whilst 

 the pileus is expanding, bends upwards and so brings the median 

 planes of the gills into approximately vertical positions. Since the 

 individual gills are wedge-shaped in cross-section, their hymenial 

 surfaces thus come to look more or less downwards. Further, as the 

 pileus expands, the gills become cleft for a certain distance down their 

 median planes, so that the cleft portion of each is shaped in cross- 

 section like the letter V- The hymenium toward the top of each gill 

 thus comes to look downwards to the earth at a considerable angle. 



The Hjonenium. — The rapid discharge of the spores, which as we 

 have seen is accomplished within about 18 hours, is brought about 

 in Psathyrella disseminata by an organisation of the hymenium that 

 is similar to that in Lepiota cepaestipes : ( 1 ) there is a reduction of 

 the number of generations of basidia to four ; (2) the four genera- 

 tions of basidia have differential protuberancy and are therefore 

 tetramorphic ; (3) there is overlapping in time in the development 

 of the sterigmata and spores in successive generations, so that the 

 four generations of basidia ripen and discharge their spores in rapid 

 succession ; and (4) the paraphyses are large and joined into a 

 definite pavement-like system, so that they fill up the spaces which 

 must necessarily be left between adjacent basidia if the latter are to 

 develop and discharge their spores without mutual hindrance. 



Illustrations of the hymenium are given in Figs. 28 and 29. In 

 Fig. 28 at A there is shown a camera-lucida drawing of a piece of the 

 hymenium, as seen in face view, in which only the spores and the 

 exhausted basidia are represented. The first two generations of 

 basidia, ab, have discharged their spores and only their collapsed 

 bodies now remain. Which of these bodies belong to the first and 

 which to the second generation one cannot now decide. The spores 

 on the third-generation basidia, c, which are all darkly pigmented 



VOL. III. 



