COPRINUS ATRAMENTARIUS 



291 



/ Tnrn 



of safety which becomes of importance when the gills are more or 

 less tilted (Fig. 124), the width of the interlamellar spaces has been 

 reduced to a mini- 

 mum. Since the 

 width of the spaces 

 is determined by the 

 length of the cys- 

 tidia, we may con- 

 clude that the length 

 of the cystidia is 

 correlated with the 

 width of the space 

 between the gills 

 required to permit 

 of the violent dis- 

 charge of the spores 

 in the region of 

 spore- discharge. 



The margin of 



safety in the width 



of the interlamellar 



spaces is drawn upon 



whenever the gills 



are inclined to the 



vertical when spore- 

 discharge is proceed- 

 ing. Since the gills 



are not positively 



geotropic, it usually 



happens that one 



side of a gill looks 



slightly upwards and 



the other slightly 



downwards during 



spore-discharge; but, even when the gills are tilted to an angle 



of 20° (Fig. 124), the spores can still escape without hindrance. 



This is provided for by the margin of safety in the width of the 



Fig. 124. — Coprinus atramentarius. Diagram illus- 

 trating the escape of spores from tilted gills. 

 Two gills are tilted at an angle of 20°. Cystidia 

 cross the interlamellar space and thus keep the 

 gills apart. The trajectories of spores shot 

 outwards from the zone of spore-discharge in 

 still air are indicated by the arrows. A, soon 

 after the beginning of spore-discharge. B and C 

 show that, owing to autodigestion of those parts 

 of the gills which have shed their spores, the up- 

 wardly-moving zone of spore-discharge is always 

 just above the gill-edge. Magnification, 22. 



