PSALLIOTA CAMPESTRIS 



383 



639. A wild mushroom which measured 9-2 cm. in diameter in 

 the fully expanded condition and which was therefore consider- 

 ably larger than the cultivated mushroom just considered, had 

 almost exactly the same number of gills, namely, 134 at the stipe 

 and 644 at the pileus-periphery. This comparison points to the 

 conclusion that on 

 equal spaces beneath 

 the pileus the culti- 

 vated mushrooms 

 tended to produce the 

 larger number of gills. 

 Let us suppose that 

 a pileus is endowed 

 with perfect radial 

 symmetry and on this 

 supposition investigate 

 the nature of its gill- 

 system. Let the num- 

 ber of long gills, i.e. 

 those which pass from 

 the stipe to the pileus- 



FIG. 137. P sail-iota campestris, cultivated form. 

 The pileus of a fruit-body photographed from 

 below immediately after its removal from a 

 mushroom bed. Notwithstanding the close 

 packing of the gill-system, there are inter- 

 lamellar spaces, into which the spores can 

 be shot, between every pair of adjacent 

 lamellae. Natural size. 



periphery, be equal 

 to x. Then, at a little 

 distance from the stipe 

 in the radial direction, 

 owing to the gradual 

 divergence of the long 



gills and the provision of the necessary interlamellar spaces, 

 we should find a second set of gills, all of exactly the same 

 length, regularly interpolated, one in each space or a total of 

 x. The number of interlamellar spaces is no\v equal to 2x. At 

 a farther distance from the stipe, we should find a third set of gills 

 interpolated, all of exactly equal length, one in each space or a total 

 of 2x. These by their presence w r ould increase the number of spaces 

 to 4x. Still farther from the stipe we should find a fourth series 

 of gills interpolated, all of exactly equal length, one in each space 

 or a total of 4x. If, still farther toward the pileus-periphery. a 



