DISPERSION BY ANIMALS 253 



tory window. The floor of the case was covered with a sheet of 

 white paper. After falling upon the latter, the ejected groups of 

 spores could be distinguished with the naked eye as tiny dark 

 specks. The maximum horizontal distance to which any of them 

 was shot was found to be about 30 cm. In violence of spore- 

 discharge possibly Ascobolus immersus is not exceeded by any other 

 Ascomycete, although it is easily beaten by Pilobolus, which can 

 squirt its sporangia to a distance of more than a metre. These 

 performances seem truly titanic when compared with those of the 

 Hymenomycetes, for the maximum horizontal distance of discharge 

 of basidiospores was observed to be only O01-0'02 cm. 1 



A group of eight Ascobolus spores clinging together was estimated 

 to have a volume about 2000 times greater than that of a single spore 

 of Amanitopsis vaginata. It is the large mass of the united asco- 

 spores which permits of the projectile receiving sufficient initial 

 velocity to carry it a distance of many centimetres. In order to- 

 shoot out a tiny Amanitopsis spore to an equal distance, a relatively 

 enormous initial velocity would require to be given to it. A parallel 

 case may be cited from everyday life. A good thrower can throw a 

 cricket ball one hundred yards. With his strongest effort, however,, 

 he can throw a small shot only a few feet. If he were determined 

 to make the shot travel as far as the cricket ball he could succeed in 

 doing so by putting it into a gun and driving it out with gunpowder. 

 The very high initial velocity which it would then receive would be 

 vastly greater than that imparted to the cricket ball, although the 

 distance traversed by both objects would be the same. It is just as 

 impossible for a man to throw a small shot a hundred yards as it 

 would be for a Mushroom to shoot out a basidiospore to a distance 

 of a single centimetre. In order to accomplish the latter feat, it 

 would be necessary for the spore to be projected with an initial 

 velocity of the order of 65 metres per second ! 2 On the other hand, 

 the united eight spores from an ascus of the Ascobolus could be shot 

 a centimetre with an initial velocity of only 0'2-0'3 metres per second. 



1 Chap. XI., Method II. 



2 Calculated by using the first equation in Chapter XVII. and taking the 

 terminal velocity of a Mushroom spore as 0'15 cm. per second (vide Chapter XVI.). 

 The spore was assumed to be spherical. 



