FRUIT-BODY FIXATION 133 



to resist bending. Under these conditions, as every engineer would 

 allow, its hollow cyhndrical form is the most efficient possible ; it 

 has the same significance as the hollow cyhndrical form of grass- 

 stems and of the upright iron columns used for supporting buildings. 

 If the stipe-shaft, with the same height and amount of material, 

 were to consist of a narrower solid cylinder, its abihty to hold the 

 pileus in a fixed position in space during the discharge of the spores 

 would be seriously impaired. The great length of the stipe-shaft 

 is of considerable biological advantage in that it permits the stipe- 

 shaft to raise the pileus high into the air, and thus to place the gills 

 in a position where they may liberate their spores so that these may 

 be carried off by the wind without interference from neighbouring 

 obstacles. 



Conclusion. — From the foregoing description of the mode of 

 development of a fruit-body of Coprinus sterquilinus it is clear that 

 the stipe becomes fixed in its faecal substratum only owing to a 

 combination of all the external and internal factors for the fixation 

 process which were summarised at the beginning of the previous 

 Section. These factors may here be briefly considered again. 

 Light inhibits the development of all the tiny rudiments of fruit- 

 bodies which happen to arise on the illuminated surface of the sub- 

 stratum, so that only rudiments which develop in dark recesses 

 beneath or between dung-balls can possibly produce mature fruit- 

 bodies. In the dark a rudiment may continue its development if 

 this is not inhibited by the growth of a more vigorous neighbouring 

 rudiment. A favoured rudiment growing in the dark at a short 

 distance below the free surface of the substratum devotes its growth- 

 energy to the development of a solid, stout stipe-base, while the 

 pileus which caps it remains small and conical, its development 

 being delayed. A negative geotropic stimulus soon causes the 

 stipe-base to push the rudimentary pileus upwards between the 

 dung-balls or through the dung-mass into the light ; and, as soon 

 as the pileus has reached the fight and with this the free upper 

 surface of the substratum, the light inhibits the further growth in 

 length of the sohd stipe-base ; and then the pileus and hollow aerial 

 stipe-shaft are developed to their full extent in succession. The 

 structure of the dung-mass, which consists of more or less spherical 



