THE PILOBOLUS GUN AND ITS PROJECTILE 87 



does not. This indicates that the upper part of the wall of the 

 subsporangial swelling, just under what is normally the line of 

 rupture when the sporangium is shot away, is highly elastic whereas 

 the wall of the columella is not. It may be added that with iodine 

 the thickened wall of the subsporangial swelling takes on a much 

 deeper red colour than the relatively thin wall of the columella. 



The globular watery drops which are formed in large numbers 

 on the sporangium and sporangiophores are well shown in Boudier's 

 drawing reproduced in Fig. 12 (p. 23), and they are also shown 

 freshly excreted and uncontracted in the diagrammatic Fig. 27 

 (p. 69). These drops, as Knoll ^ discovered, resemble those on the 

 pileal hairs of Coprinus ephemerus and Psathyrella disseminata, etc., 

 and on the gills of various Hymenomycetes, in that they contain a 



Fig. 43. — Pilobolus longipes. From left to right, diagrammatic representa- 

 tion of two drop.s excreted from a sporangium, and of successive stages 

 in their d rying up. As the drops dry, they shrink in size, become irregular 

 in form (owing to their gelatinous contents), and finally become as black 

 as the sporangium-wall. Magnification, 100. 



pellucid colloidal substance or slime — readily soluble in water but 

 insoluble in alcohol— which gives to the surface of the drops, as 

 these dry up, an irregularly wrinkled appearance. ^ With the help 

 of the microscope I myself have often observed the wrinkling of 

 the drops of Pilobolus as they lose water by evaporation (Figs. 42, C, 

 and 43). 



The drops on the sporangium and upper part of the subsporangial 

 swelling usually dry up, leaving in their places tiny irregular gela- 

 tinous masses, before the sporangium is discharged (Fig. 42, C), 

 Doubtless, whilst they exist as large watery spheres, they interfere 

 to some extent with the course of the rays of light entering the 

 subsporangial swelling. Their early disappearance must therefore 

 be of advantage in that it enables the sporangiophore to direct the 



^ F. Knoll, " Untersuchungen iiber den Bau und die Funktion der Cystiden 

 und verwandter Organe," Jahrb.f. wiss. Bot., Bd. L, 1912, pp. 453-501. 



^ For drops. on the pileal hairs of Coprinus curtus and their mode of drying 

 vide these Researches, Vol. IV, 1931, Fig. 12, p. 18. 



