THE SPHAEROBOLUS GUN 359 



physiological properties of the Sphaerobolus gun and projectile, 



(2) the fact that the fungus under natural conditions is not infre- 

 quently found on the dung of various herbivorous animals, and 



(3) the fact that the fungus grows and fruits well on horse dung in 

 laboratory cultures, I have been led to the conclusion that Sphaero- 

 bolus 'primarily is a coprophilous fungus and that its occurrence on 

 wood, while due occasionally perhaps to the germination of glebae 

 which have been shot on to the surface of the wood from neighbour- 

 ing fruit-bodies, must in general be accomplished through the agency 

 of animals. A discussion of the manner in which Sphaerobolus 

 comes to infect wood will be deferred to a subsequent Section. In 

 the meanwhile an attempt will be made to show how Sphaerobolus 

 resembles two other unrelated fungi which exhibit special adapta- 

 tions for a coprophilous mode of existence. 



Pilobolus, Ascobolus immersus, and Sphaerobolus as Three Fungi 

 with Parallel Adaptations for a Coprophilous Mode of Life. — It is a 

 remarkable fact and an illustration of parallelism in the course 

 of organic evolution that in Pilobolus, Ascobolus immersus, and 

 Sphaerobolus, three fungi which belong respectively to the Phyco- 

 mycetes, the Ascomycetes, and the Basidiomycetes — the three 

 great divisions of the Fungi proper — the sporocarps are either 

 converted directly into guns (Pilobolus, Sphaerobolus) or else pro- 

 duce guns (Ascobolus immersus) which have many characteristics 

 in common (Fig. 172). Let us now consider what these characteris- 

 tics are. 



(1) Massiveness and Parabolic Trajectory of the Projectile. The 

 Pilobolus, 1 Ascobolus immersus, 2 and Sphaerobolus guns all shoot 

 away projectiles which are relatively massive, so massive indeed 

 that, immediately after leaving the guns, they are not carried off 

 by the wind as are the ascospores of the Pezizae and most species of 

 Ascobolus 3 or as are the basidiospores of the Uredineae, Tilletia, 



1 For a description of the Pilobolus gun and projectile, vide these Researches in 

 the forthcoming Volume VI. 



2 For a description of the guns and projectiles of Ascobolus immersus, vide these 

 Researches, Vol. I, 1909, pp. 251-257. 



3 In most species of Ascobolus, e.g. A. stercorarius, A. magnificus, the eight spores 

 of each ascus are relatively very small and they separate from one another as they 

 pass out of the ascus mouth, so that they are carried away by the wind individually. 



