26 RESEARCHES ON FUNGI 



forms the drop. Possibly, therefore, the formation of a drop is 

 merely the outward and visible sign of the weakening of the 

 cell-wall which takes place in preparation for spore-discharge, 

 and is nothing more than a necessary physical accompaniment 

 of an alteration in the chemical or physical condition of the 

 cell- wall. 



The drop of water is always carried away by the spore at the 

 moment of its discharge. This is not surprising since the hilum 

 which excretes the drop is part of the spore. From the physical 

 point of view it is therefore clear that the drop serves to increase 

 the mass of the projectile. This increase of mass doubtless permits 

 of the spore being shot further from the basidium than it would be 

 without the addition of water to it. After a spore has reached an 

 interlamellar space and begins to fall vertically, the water-drop 

 very quickly dries up, so that it does not hasten the fall of a spore 

 to the ground. One must admit, therefore, that the drop of water 

 is useful in that, by increasing the projectile-mass, it assists the 

 sterigma in its work of shooting the spore to a safe distance from 

 the hymenium before the spore begins to fall vertically. The 

 fluid which in Pilobolus clings to the sporangium, and which in 

 Empusa, Ascobolus, and Peziza clings to the spores, is certainly 

 of considerable importance as a means of increasing the projectile- 

 mass, and thereby of increasing the distance to which the mass 

 can be shot. 1 I am inclined, however, to think that, while the 

 drop excreted at the hilum of the spore in Hymenomycetes does 

 increase the mass of the projectile and thus permits of the pro- 

 jectile being shot a little further than it otherwise would be, this is 

 only an incidental advantage and does not give us a clue to the 

 primary significance of drop-excretion. 



It may be that the force of surface tension is used in some way 

 to effect spore-discharge ; but exactly how I cannot satisfactorily 

 explain. Possibly we have an entirely new principle involved in 

 the mechanism of spore-discharge in the Hymenomycetes which, 

 when properly elucidated, will prove of the highest interest and 

 once more show how organisms are able to avail themselves of the 

 forces of nature in order to maintain their existence. 



1 Cf. vol. i, 1909, Part II, Chap. II, pp. 25S-254. 



