THE PILOBOLUS GUN AND ITS PROJECTILE i6i 



drops of water were allowed to fall from a tap on to some of the 

 sporangia ; and the plate was so arranged that the stream of water, 

 after leaving the sporangia, ran over the postage stamp. The 

 postage stamp was washed off the plate in 3 • 5 minutes, whereas 

 the sporangia withstood the impact of the drops for half an hour. 



The effectiveness of the gelatinous ring in enabling the sporangium 

 to cling to its substratum even when battered by large drops of 

 water as in the experiments just described appears to be due to the 

 fact that the jelly, after being dried and placed in water again, 

 swells up by the absorption of water but only to about its original 

 volume, so that, unlike the mucilage on a postage stamp, it does 

 not dissolve in water. 



From the observations just recorded we may conclude that, 

 under natural conditions in pastures, the sporangia are so effectively 

 attached by their gelatinous bases to the herbage on which they have 

 alighted that, in dry weather, they cannot be detached from their 

 substrata by the strongest winds and, in wet weather, they cannot 

 easily be detached by prolonged rain or even by violent thunder- 

 storms. 



The Relations of Pilobolus with Flowering Plants and with 

 Herbivorous Animals. — Pilobolus is a highly specialised copro- 

 philous fungus which is dependent for its existence : firstly, on 

 flowering plants which provide its sporangia with a temporary but 

 prospectively favourable lodging-place and, secondly, on herbivorous 

 animals which swallow the sporangia and herbage together, break 

 open the sporangia and disperse the spores within their alimentary 

 canals, and finally extrude the spores undamaged in their solid 

 faeces. The spores, thus sown in dung-plats in pastures, rapidly 

 germinate, and the mycelia to which they give rise soon develop 

 new fruit-bodies which, in their turn, shoot away their sporangia 

 on to the surrounding herbage (Fig. 79). 



The smaller sporangia of Pilobolus Kleinii and of P. longipes are 

 often shot to a horizontal distance of 3-5 feet whilst the largest ones, 

 as we have seen, are sometimes shot a horizontal distance of about 

 8 feet. Therefore, when fruit-bodies of these species are growing on 

 a dung-plat in a pasture, hundreds of sporangia may be, and often 

 actually are, shot away so as to dot the leaves and stems of grasses 



VOL. VI. M 



