398 RESEARCHES ON FUNGI 



formation of fruit-bodies ; for, as every mushroom-grower knows, 

 mushrooms can be reared in perfectly dark cellars and caves where 

 not a ray of light enters. When the mycelial strands approach 

 the surface of the soil, they are liable to lose considerable quantities 

 of water by transpiration, for the free air above the soil is usually 

 much less moist than the air in the soil. This increased transpira- 

 tion may well be one of the conditions favouring fruit-body forma- 

 tion. The production of fruit-bodies at the surface of the soil may 

 be due in part to a stimulus provided by the gaseous environ- 

 ment. The soil must be considerably richer in carbon dioxide 

 and other gases produced by the decomposition of organic matter, 

 and at the same time poorer in oxygen, than the free air above it. 

 Another point of difference between the gases in the soil and those 

 of the free air is that the latter are in constant motion owing to air 

 currents and the wind, while the former are relatively still. If 

 the change of gaseous environment should be shown by future 

 experiment to be the cause of the formation of fruit-bodies at the 

 surface of the soil, its exact mode of operation will require detailed 

 analysis. At or very near to the surface of the soil the mycelial 

 strands are freer from mechanical pressure than well below it ; 

 and it is therefore possible that mechanical freedom is also a factor 

 in deciding the place of origin of the fruit-bodies. Here again 

 there is room for an experimental enquiry. 1 



The Fate of Rudimentary Fruit-bodies. On artificial mushroom- 

 beds, a great many rudimentary fruit-bodies are produced for 

 every one that comes to maturity : ' many are called, but few are 

 chosen." Perhaps there are at least fifty rudimentary fruit-bodies 

 brought into existence for every one which ultimately liberates 

 spores. No doubt the same thing happens in nature, although in 

 pastures it is usually impossible to observe any fruit-bodies at all 

 in their very earliest stages of development, owing to their being 

 hidden by herbage. It seems to me that there is a considerable 

 advantage in the formation of so many rudiments, notwithstanding 

 that the vast majority of them are always destined to suffer 

 abortion. The surface of the ground is an external condition 



1 For an experimental enquiry into the cause of the position of origin of the 

 fruit-bodies of Coprimis sterqmlimis, vide vol. iii, Chap. IV. 



