PSATHYRELLA DISSEMINATA 45 



water, persist in 95 per cent, alcohol.^ The excretion, according to 

 this observer, is of a colloidal nature. 



The pileus, on expanding, becomes campanulate and then soon 

 begins to discharge its spores. Its diameter in the fully expanded 

 condition varies from 1 to 1-5 cm. Whilst the expansion is taking 

 place, the colour of the pileus changes from whitish or pale buff 

 to grey, except at the disc which becomes yellowish. The yellow 

 colouring matter of the disc is deposited in certain of the projecting 

 hair-cells. The cells which make up the firm outer palisade layer 

 of the pileus grow rapidly in size during the expansion of the pileus 

 and, in consequence, the hairs situated between them become corre- 

 spondingly more scattered and less noticeable. The loose spherical 

 cells also tend to disappear from the pileus. In Massee's description 

 the pileus is said to be " at first scurfy, then naked." For field 

 purposes this may be taken as true, although careful search reveals 

 some prominent or collapsed hairs on the surface of the pileus to 

 the very last. The pileus, whilst becoming campanulate, splits 

 radially from above downwards along the lines of the gills, more 

 particularly along those of the larger ones. It thus becomes plicate 

 in the same manner as the pileus of Coprimis plicatilis or C. curtvs. 

 A cleft gill in cross-section resembles the shape of the letter Y. 

 The radial cleavages, which are about thirty in number altogether, 

 permit of the rapid expansion of the pileus without any correspond- 

 ing growth of the pileus-flesh ; and, indirectly, they also serve to 

 bring into existence suitable interlamellar spaces for the discharge 

 of the spores. The flesh of the pileus is thickest at the disc where, 

 by suitable growth-movements, it serves the purpose of opening 

 out the pileus. The flesh on the sides of the pileus is extremely 

 thin ; and, although when the pileus is very young and ovate it 

 forms a continuous sheet, yet when the pileus opens out it becomes 

 split intQ a series of radial ribbons, each ribbon supporting one-half 

 of each of two adjacent long gills and often, in addition, the whole of 

 a very short gill.^ 



^ Loc. cit., pp. 463-464. 



2 It is a mistake to suppose that there is no pileus-flesh on the sides of the pilei 

 of Psathyrella disseminata, Coprinus plicatilis, etc. Gills are projections of the flesh, 

 which extend the area on which the hymenium may be developed. If, in either of 

 these two fungi, the gills were removed from the young and unexpanded pileus, we 



