GENERAL SUMMARY 383 



Unopened fruit-bodies can withstand desiccation for several months. 

 The projectile is resistant to the disintegrating action of rain-water. 



Light acts on Sphaerobolus in several different ways : (1) it is essential 

 for fruit-body formation, (2) it causes the fruit-body to develop so that 

 its apex faces the strongest incident rays of light, (3) it causes the fruit- 

 body to open in the day instead of at night, and (4) it increases the 

 vigour with which a fruit-body discharges its projectile. 



Sphaerobolus has been found not only on wood but also on the dung 

 of elephants, horses, cows, hares, and rabbits. The fungus therefore is 

 not only xylophilous but also coprophilous. 



At Winnipeg Sphaerobolus stellatus has been found in the months of 

 October and November growing and fruiting freely on old cow-dung 

 plats in pastures. 



It is a remarkable fact and an illustration of parallelism in the course 

 of organic evolution that in Pilobolus, Ascobolus immersus, and Sphaero- 

 bolus, which belong respectively to the Phycomycetes, the Ascomycetes, 

 and the Basidiomycetes — the three great divisions of the Fungi proper — 

 the sporocarps are either converted into guns directly (Pilobolus, Sphaero- 

 bolus) or else produce guns {Ascobolus immersus), which have many 

 characteristics in common, namely, (1) massiveness and parabolic 

 trajectory of the projectile, (2) great violence in the discharge of the 

 projectile, (3) adhesiveness of the projectile, (4) heliotropism of the guns, 

 (5) multisporous nature of the projectile and non-separation of the spores 

 whilst the projectile is attached to herbage, and (6) occurrence of the gun- 

 developing fruit- bodies on the dung of herbivorous animals. These 

 characteristics are correlated, for they are all associated with the dispersion 

 of the spores by herbivorous animals. 



So far as the arrangements for securing the dissemination of the spores 

 are concerned, coprophilous fungi may be divided into two groups : 

 (1) a more primitive group which successively makes use of three external 

 agents — the wind, flowering plants, and herbivorous animals — and (2) a 

 more highly specialised group which dispenses with the wind and which 

 successively makes use of only two external agents— flowering plants and 

 herbivorous animals. To the first group belong Aleuria vesiculosa, 

 Ascobolus stercorarius , Stropharia semiglobata, and Coprinus sterquilinus ; 

 while to the second more specialised group belong Pilobolus, Ascobolus 

 immersus and Sphaerobolus. 



The manner in which Sphaerobolus comes to infect wood has been 

 discussed. Wood may become infected (1) by means of glebal masses 

 shot on to it from fruit-bodies growing on another piece of wood or on 

 dung or (2) by mycelium growing on to it from infected dung. It also 

 seems possible that wood may become infected by spores, or possibly 

 gemmae, which have passed through the alimentary canal of some 

 herbivorous animal and have then been transferred to wood by dung-flies. 



