74 RESEARCHES ON FUNGI 



edge of the wall and the columella (Fig. 30, B and C). The real 

 significance of dehiscence in Pilobolus Ues in this : that, whereas 

 it does not permit of the escape of the spores from the sporangium, 

 it leads to the exposure of the gelatinous ring which, as wie shall see 

 later, has the function of attaching the sporangium with its enclosed 

 spores to the herbage on which herbivorous animals feed. The 

 escape of the spores from a Pilobolus sporangium does not take place 

 when the sporangium dehisces but only when the sporangium, 

 having been eaten with grass by horses or cows, etc., is moistened 

 and compressed in an aUmentary canal. It is of interest to note 

 that the swelhng up and exposure of the gelatinous ring on the 

 outside of the sporangium is beautifully timed, for it takes place 

 only a few minutes before the sporangium is discharged and the 

 ring is to function in the service of spore-dispersion. 



It was observed that, when a pane of glass is set just in front of 

 a large number of fruit-bodies of Pilobolus longipes, so that the 

 sporangia are shot against it, the force of the impact is so great that 

 sometimes a sporangium is sUghtly shattered to the extent that 

 (1) a few spores may be forced out of the sporangium owing to the 

 displacement of the gelatinous ring and (2) fragments of the peri- 

 pheral less darkly-coloured portion of the black sporangial wall may 

 be broken away from the main mass of the wall. The escaped 

 spores and the broken wall-fragments can then be seen lying in 

 the drop of cell-sap which forms a halo around the sporangium 

 (c/. Fig. 33). Under natural conditions in the open, the sporangia 

 are shot not against substances as hard and inelastic as glass but on 

 to herbage and, normally, after they have landed they contain their 

 full complement of spores. There is every reason to suppose that, 

 in pastures and woods, the partial rupture of a Pilobolus sporangium 

 due to impact on landing occurs either not at all or only as a rare 



accident. 



The number of spores contained in the sporangium of Pilobolus 

 oedipus (Cohn's P. crystallinus) was estimated by Cohn ^ to be 

 15,000-30,000, and Coemans ^ remarked that this estimate did not 



1 Ferdinand Cohn, " Die Entwicklungsgeschichte des Pilobolus crystallinus," 

 Nova Acta Acad. Caes. Leop., Bd. XXIII, 1851, p. 513. 



2 E. Coemans, " Monographic du genre Pilobolus," 1861, loc. cit., p. 25. 



