380 RESEARCHES ON FUNGI 



The result would be that the beginning of spore-discharge would 

 need to be considerably delayed or, if spore-discharge were to take 

 place during the expansion of the pileus, there would be a great 

 waste of spores, for a large proportion of the discharged spores 

 would strike the gill-sides, adhere there, and never be carried off 

 by the wind. One perceives that, with a concentric arrangement 

 of the gills, the adjustments for securing that the hymenium shall 

 look more or less downwards would be necessarily more complex, 

 take longer to complete, and allow of less elasticity than with the 

 radial arrangement. 



(2) The peripheral boundary of the pileus of a Mushroom 

 increases very greatly and rapidly as the pileus expands. If the 

 gills, instead of having the radial arrangement, had the concentric 

 one, the amount of stretching to which the gills would be subjected 

 during the expansion of the pileus would be by no means equal, 

 but would increase progressively and considerably from the inner- 

 most gill surrounding the stipe to the outermost gill at the periphery 

 of the pileus. During the rapid expansion of the pileus, the outer- 

 most gills in particular would be subjected to great strain, and only 

 by extraordinarily rapid growth could they respond to the demands 

 made upon them by the rapid increase of the pileus-periphery. 

 During the expansion of the pileus, the innermost concentric gills 

 would require to lengthen their circumferences only very slightly, 

 but the outermost ones would require to lengthen theirs relatively 

 enormously. I cannot help thinking that the concentric arrange- 

 ment of the gills, which would involve such an inequality in the 

 development of the gills, would result in inefficiency in the produc- 

 tion of spores, and that the radial arrangement, where all the gills 

 are equally stretched in the radial direction, is on this account 

 much to be preferred. 



For the reasons given above we may conclude that the radial 

 arrangement of the lamellae, as we actually have it in a Mushroom, 

 is most beautifully adapted to secure the highest efficiency in the 

 production and liberation of the spores. 



The radial arrangement of the gills comes into existence during 

 the development of the pileus in the following manner. The first 

 gills to make their appearance in the very rudimentary pileus are 



