128 RESEARCHES ON FUNGI 



the limitation in the quantity of nutrient substances stored up 

 within the mycehum of the dung-balls. Certain rudiments are 

 therefore selected for further development. The selection takes 

 place in two stages. 



The first selection of fruit-body rudiments is carried out as 

 follows. All the illuminated rudiments on the upper exposed 

 surfaces of the substratum are prevented from growing beyond the 

 size of a pin's head by the inhibitory action of hght. The result 

 of this is that, under natural conditions, no mature fruit-body can 

 ever come into existence with the base of its stipe seated directly upon 

 the top or exposed upper sides of a dung-ball. Such a position, as 

 experiments with cultures kept entirely in the dark have shown, 

 would be so insecure that the fruit-bodies as they grew in length 

 would topple over by their own weight and be ruined physiologically. 

 The inhibitory action of the light on the tiny rudiments, therefore, 

 prevents fruit-bodies from ever taking up the insecure positions 

 indicated. 



The rudiments remaining after the first selection are those which 

 have arisen on darkened surfaces, i.e. in darkened crevices on the 

 under sides of the dung-balls. At first, these rudiments are 

 numerous ; but, by means of a second selection, only one or a very 

 few of them are permitted to undergo further development. This 

 second selection depends on nutrition and mechanical opportunity. 

 If the mass of dung which is infected with the mycehum is large, 

 then several fruit-bodies — each one as a rule distantly situated from 

 its nearest neighbours — may come to maturity ; but, if the infected 

 substratum is limited to one or a very few dung-balls, then only 

 one fruit-body may be ultimately produced. Those rudiments 

 which happen to occupy the most favourable situations in respect 

 to the mycelium and to free space for growth obtain the most 

 nutriment, grow fastest, and are those which are destined to sur- 

 vive and attain maturity. The more vigorous development of 

 one rudiment causes the entire inhibition of growth of all the smaller 

 neighbouring rudiments within a certain radius. This inhibition 

 of growth appears to be due to starvation : a favoured rudiment 

 robs its less fortunate companions of the food substances which 

 would otherwise fall to their share. The contents of the mycehum 



