THE ARRANGEMENT OF GILLS 35 



untilted pileus. 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- r 1 ^ 



ceeds a certain maximum their arrange- V * 



merit is a wasteful one, for the underside 



of the pileus is then not being used up to 



the best advantage. The gills of Agaricineae 



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 Flo . 8 ._ As( ,,,,,of,iii s removed 



never exceed a certain maximum width, SaShrSSi $Soio* *$? 



<rw). Natural size. 



