THE ARRANGEMENT OF GILLS 



55 



untilted pilous. This arrangement must be 

 of some value, for in woods and fields slightly 

 tilted pilei with vertical gills are quite com- 

 monly met with. 



It is now clear that two adjacent gills 

 must be at least a certain minimum distance 

 apart to permit of the successful liberation 

 of the spores. It is equally clear, however, 

 that when the space between two gills ex- 

 ceeds a certain maximum their arrange- 

 ment is a wasteful one, for the underside 

 of the pileus is then not being used up to 

 the best advantage. The gills of Agaricinese 

 are disposed radially, so that in passing from 

 the stipe to the edge of the pileus they 

 necessarily diverge. Near the stipe two 

 adjacent gills may be economically spaced. 

 Further from the stipe, however, owing to 

 divergence, their spacing becomes wasteful. 

 There is much more room left between them 

 than is necessary for the liberation of the 

 spores, and for the provision of an adequate 

 margin of safety. This defect is obviated 

 almost entirely in most Agaricinese by the 

 introduction of shorter gills between the 

 longer ones, in succession, proceeding from 

 the stipe to the pileus periphery (Fig. 8). 

 In some specimens of Marasmius oreades 

 it was found that the gills were of three 

 different lengths, and that in a specimen 

 of Tricholoma personatum they were of four 

 different lengths. The complexity of the 

 gill-system is usually greatest in pilei with 

 large diameters. Good examples of the 

 economical arrangement of gills, so that 

 the space between any adjacent two shall 

 never exceed a certain maximum width, 



C? 



Fig. 8.— A series of gills removed 

 from the pileus of a field 

 Mushroom (Psalliota campes- 

 tris). Natural size. 



