GENERAL SUMMARY 269 



The Hymenomycetes, owing to the possession of basidia, are better 

 organised for the production of large fruit-bodies which discharge their 

 spores into the air than Ascomycetes. This is due to the fact that, 

 without interfering with the escape of the spores, a hymenium contain- 

 ing basidia can be more compactly folded than one containing asci. 

 The present dominance of large-fruited Hymenomycetes over large- 

 fruited Ascomycetes in forests and fields may be indirectly due to the 

 fundamental difference between basidia and asci as spore-discharging 

 mechanisms. 



CHAPTER II. Ascobolus immersus is specially adapted to a coprophilous 

 ^mode of existence. The special adaptations of its fruit-bodies are : (1) The 

 protrusion of the ripe -asci beyond the general surface of the hymenium, 



(2) the diurnal periodicity in the ripening of successive groups of asci, 



(3) the positive heliotropism of the asci, (4) the considerable distance to 

 which the spores are ejected (sometimes 30 cm.) with which is associated 

 (5) the large size of the asci and spores, and (6) the clinging of the eight 

 spores together whilst describing their trajectory through the air. The 

 adaptations are such as to permit of the asci discharging their contents 

 so that these may be shot outwards clear of immediate obstacles, such 

 as dung balls, fec., and fall on the surrounding grass where they may be 

 swallowed by herbivorous animals. 



The projectiles of Ascobolus immersus, Empusa, and Pilobolus are much 

 larger than those of the Hymenomycetes. The distance to which they are 

 ejected is proportional to their size. 



The clinging together of the eight spores in the ascus of Ascobolus 

 immersus involves an increase in the mass of the projectile, and thereby 

 enables the spores to be shot to a greater distance than that to which they 

 would be shot if they separated from one another immediately after leaving 

 the ascus mouth. 



When sporangiophores of Pilobolus longipes are inclined upwards at an 

 angle of about 45, the sporangia are often thrown to a horizontal distance 

 of 5 feet. The maximum horizontal distance of ejection observed was 

 6 feet 2 inches. 



Grove's observation that the sound of the discharge of the sporangia 

 from the sporangiophores is audible, has been confirmed. Another sound 

 can be detected when the sporangia strike against a glass vessel or a piece 

 of paper. The impingement of sporangia upon a tissue paper drum could 

 be distinctly heard at a distance of 21 feet. 



Attempts to detect a sound proceeding from fruit-bodies of the Mush- 

 room and Polyporus squamosus, when discharging about a million spores 

 a minute, failed. Probably for unaided human ears, the liberation of the 

 spores of Hymenomycetes will for ever remain a quite silent process. 



