REMARKS ON THE PILOBOLIDAE 183 



apparently terminal basal swellings in reality have originated in 

 an intercalary manner (Fig. 90, C ; also Fig. 21, E-G, p. 52), yet 

 it may well be that now and again some basal swellings originate 

 in a truly terminal manner, for Cohn ^ (1851) observed in Pilobolus 

 oedipus certain club-shaped hyphae coming off from stout hyphae, 

 which he considered to be the possible beginnings of new fruit- 

 bodies, and I have observed exactly similar club-shaped hyphae in 

 the mycelium of P. umbonatus (Fig. 90, D, / and g). 



The ratio of the width of the sporangium to the width of the 

 subsporangial swelling in the fruit-body of a Pilobolus may be called 

 the width-ratio. To obtain the data for this ratio, all that one needs 

 to do is to remove a fruit-body from a culture, to lay it horizontally 

 in a drop of water on a glass slide, and then to measure in succession 

 the width of the sporangium and the width of the subsporangial 

 swelling. 



A preliminary study of the width-ratio of three species of Pilo- 

 bolus wac^ made under my direction by Dr. Dowding, and the results 

 of it are embodied in the diagram reproduced in Fig. 91. The upper 

 five drawings at A show in top view the sporangia of five wild fruit- 

 bodies of Pilobolus longipes ; their average width-ratio was found 

 to be approximately f . The lower five drawings at B show five 

 sporangia obtained from a pure culture of P. Kleinii ; their average 

 width-ratio was found to be approximately f. The drawing C 

 shows a single sporangium of a wild fruit-body of P. umbonatus ; 

 its ratio was found to be — as in other fruit-bodies of this species — 

 approximately J. Thus the average ratio of the width of the 

 sporangium to the width of the subsporangial swelling appears to 

 differ appreciably in the three species of Pilobolus which have been 

 investigated. 



Lepeschkin ^ found that the width of the subsporangial swelling 

 in a Pilobolus is determined in part by the osmotic value of the 

 substances dissolved in the water permeating the substratum. On 



^ F. Cohn, " Die Entwicklungsgeschichte des Pilobolus crystallinus," Nova Acta 

 Acad. Cues. Leop., Bd. XXIII, 1851, Plate LII, Figs. 14 and 16. His P. crystallinus 

 was in reality P. oedipus. 



2 W. W. Lepeschkin, " Zur Kenntnis des Mechanismus der aktiven Wasseraus- 

 scheidung der Pflanzen," Beihefte z. Bot. Centralb., Bd. XIX, 1906, p. 423. Also 

 vide supra, p. 34. 



