254 



RESEARCHES ON FUNGI 



The initial velocity which an ascospore group would need to have 

 imparted to it in order to fall 30 cm. from a fruit-body would be less 

 than 10 metres per second. 1 



From the above discussion it seems that a chief factor in securing 

 a sufficiently large trajectory for the ascus contents of Ascobolus 



immersus is the large mass of the 

 projectile. The projectile owes its 

 size to four factors: (1) The unusually 

 large size of the spores, (2) the 

 thick gelatinous envelope round 

 each spore, (3) the clinging of the 

 spores together, and (4) the large 

 mass of the discharged ascus sap. 

 The spores, excluding their gela- 

 tinous investments, measure 35-45 

 X 55-65/i, and therefore are 50-100 

 times greater in volume than the 

 wind -borne spores of Peziza entr- 

 ant ia. The gigantic size of the 

 spores as compared with those of 

 the Hymenomycetes will at once be 

 realised by a glance at Fig. 82. 



In Pilobolus, where the unopened 

 sporangium is squirted off the spor- 

 angiophore, the projectile is rela- 

 tively of great size. That it should 

 be shot out farther than the contents of any ascus is, for the 

 mechanical reasons already discussed, not in the least surprising. 

 Empusa muscze, as is well known, can send its unicellular conidia 

 to a distance of some centimetres. Here, however, the spores 

 are not only very large but become coated with a thick and sticky 

 fluid discharged from the conidiophore. The large size of the 

 projectile may be at once recognised from the accompanying photo- 

 graph (Fig. 83). 



Fig. 82. — Comparative sizes of fungus 

 projectiles, a, spore mass of Ascobolus 

 immersus ; b, spores of Amanitopsis 

 vaginata ; c, spores of Colh/bia dryo- 

 phila ; d, spores of Psalliota cam- 

 jjestris ; e, spores of Coprinus comutus. 

 All drawn to the scale given. 



1 Here the terminal velocity was taken to be 30-50 cm. per second {vide infra). 

 The spore-group was assumed to be spherical. The calculations are only very 

 rough approximations to actual values. 



