COPRINUS STERQUILINUS 253 



the vertical to an angle of 30° and yet all the spores would escape 

 from the pileus. The reader will realise the truth of this statement, 

 if he or she imagines that the three gills shown in Fig. 101, A, 

 (p. 237) have been tilted to the extent postulated, and that the 

 horizontal component of the sporabolas there shown remains un- 

 changed ; for it will be evident that, when the spores shot out from 

 the zone of spore-discharge fall vertically downwards, they will 

 not strike the gill-edges but fall clear of them. 



That the spores of Coprinus sterquilinus can escape freely from 

 gills which are tilted from the vertical at a considerable angle is 

 also clear from a study of the spore-deposit shown in Fig. 102 (p. 238). 

 That spore-deposit was made by removing an expanded pileus from 

 its stipe and setting it on white paper. The pileus rested on the 

 peripheral parts of its gill-edges ; its gill-planes could not have 

 occupied exactly vertical positions ; and yet, as the double spore- 

 lines prove, spores escaped freely from both edges of each tilted gill 

 and formed excellent spore-deposits on the paper below. 



Under natural conditions in the open the gills of Coprinus ster- 

 quilinus are usually tilted slightly from the vertical ; but, as we have 

 seen, a tilt of 5°, 10°, or even 20°, cannot make any appreciable 

 difference to the freedom with which the spores escape from the 

 pileus. 



That under natural conditions the planes of the gills tend to be 

 more or less tilted from the vertical is due to the fact that the gills 

 are subparallel-sided and ageotropic. The gills develop in the 

 first place within the pileus and about the stipe in a series of radial 

 planes ; and the stipe, on becoming negatively geotrojDic, turns 

 upwards and thus brings the pileus as a whole into an upright 

 position {cf. Fig. 75, p. 186, where the stipe is bent owing to its 

 re-action to gravity and the pileus is now upright). The result of all 

 this is that, just before spore-discharge begins, all the gills come 

 to lie in planes which are not absolutely vertical but only more or 

 less so. Since the gills are ageotropic, they cannot adjust their 

 positions in space so as to make them quite vertical. However, 

 there would be no advantage in their making this fine adjustment, 

 even if they could ; for, as we have seen, the mechanism for the pro- 

 duction and liberation of the spores is of such a kind that the spores 



