36 RESEARCHES ON FUNGI 



and yet never be less than a certain minimum width, are seen 

 in the Oyster Fungus (Pleurotus ostreatus, Figs. 2 and 3) and 

 in the Mushroom (Fig. 9 and Plate IV., Fig. 25). Certain species 

 of Russula have gills which are all of one length, with the 

 exception of very occasional shorter ones (Fig. 10). Since the 

 gills in the fully-expanded fruit-bodies diverge considerably in 



Fig. d.—Psalliota campestris. Part of Fig. 10. — The pileus of Russula nigricans — 

 a pileus photographed from below, an Agaric iu which the gills are very 



showing that the gills are accu- coarsely spaced. The stipe is maggot- 



rately adjusted so that they look eaten. Reduced to \ natural size, 



directly downwards. Natural size. 



passing from the stipe to the margin of the pileus, their arrange- 

 ment appears to be relatively imperfect. 



The principles underlying the arrangement of the gills of the 

 Agaricinea3 doubtless also apply to the arrangement of the hymenial 

 tubes beneath the pilei of species of Polyporea?. Other things 

 being equal, the greatest economy is effected when the tubes are 



