132 RESEARCHES ON FUNGI 



are differently located : a short stipe-base which is sohd and fixed 

 within the faecal substratum, and a long stipe-shaft which is hollow 

 and projects upwards in the air. The mechanical functions of the 

 stipe-base are : (1) to push up the young pileus into the light, 

 (2) to hold the whole fruit-body firmly fixed in one position during 

 the development of the stipe-shaft and pileus, and (3) to support 

 the weight of the stipe-shaft and pileus even when these are full- 

 grown. On the other hand, the stipe-shaft has but one mechanical 

 function — that of supporting the pileus. The differences in the 

 structure of the stipe-base and of the stipe-shaft are correlated 

 with the different functions which these organs carry out. Each 

 organ has to withstand a particular set of mechanical stresses and 

 strains. The sohdity of the stipe-base is advantageous because 

 the stipe-base is subjected to : (1) lateral compression from opposing 

 parts of the substratum in crevices when the stipe-base is under- 

 going its initial thickening ; (2) longitudinal compression from the 

 weight and resistance of the substratum during the raising of the 

 pileus upwards into the light ; (3) longitudinal compression, sub- 

 sequently, from the weight of the full-grown stipe-shaft and pileus ; 

 (4) lateral compression or crushing strains arising from the dung- 

 balls which the stipe-base during its growth in length has forced 

 somewhat apart ; and, finally, (5) irregular strains, due to the 

 weight of the stipe-shaft and pileus and the action of the wind upon 

 these organs, which have a tendency to force the stipe-base laterally 

 out of its original position. Evidently, the mechanical demands 

 made upon the stipe-base owing to the various strains and stresses 

 just enumerated, which tend to crush it either longitudinally or 

 laterally, are very considerable ; and it seems, therefore, only in 

 accordance with the fitness of things that the stipe-base should be 

 a soUd and not a hollow cyhnder. The length of the stipe-base just 

 suffices to allow this organ to come to the upper Ughted surface of 

 the substratum. It is within the substratum that the greatest 

 mechanical strains and stresses operate ; and it is precisely within 

 the substratum that the stipe-base is situated. The stipe-shaft is 

 hollow and long. Since it is aerially situated, it does not require 

 to withstand lateral crushing strains Uke those to which the stipe- 

 base is subjected, but only to support the weight of the pileus and 



