56 RESEARCHES ON FUNGI 



p. 210), all of which came up in the horse-dung cultures just described, 

 and P. oedipus which fruited freely on a cake of drying mud brought 

 to the laboratory from the banks of the Red River. The species 

 chiefly used for observation were P. Kleinii and P. longipes. Pilo- 

 bolus umbonatus will be described in Chapter III. Pilobolus 

 crystallinus, so far as I know, has never come up in any of my 

 cultures. 



General Description of the Pilobolus Gun and its Projectile. — 

 As is well known, the sporangiophore of Pilobolus shoots away its 

 sporangium to a distance of several feet and therefore acts as a gun. 

 The gun, as shown in Fig. 2 (p. 4), consists of three parts : (1) a 

 basal swelling which, with the aid of mycelial hyphae, serves to fix 

 the gun firmly to the substratum ; (2) a slender cylindrical stipe, 

 several millimetres long, which by means of a heliotropic response 

 serves to lay the gun in the direction in which it is to be discharged ; 

 and (3) a large oval subsporangial swelling which acts as part of a 

 squirting apparatus and also, as will be shown later, as an ocellus 

 which perceives the direction of the incident light and thereby 

 assists the stipe in its heliotropic movements. The projectile — the 

 sporangium — is seated on the free end of the subsporangial swelling, 

 is discoid, is covered with an intensely black membrane, and con- 

 tains many thousands of spores. Photographs of some Pilobolus 

 guns which are about to discharge their projectiles are shown in 

 Figs. 5, 13, and 18 (pp. 8, 37, and 50). 



In every species of Pilobolus, the diameter of the subsporangial 

 swelling much exceeds that of the sporangium and still more that 

 of the stipe. This may be realised by reference to Fig. 22 which 

 shows a plan of cross-sections of these parts for typical large fruit- 

 bodies of Pilobolus longipes and P. Kleinii. 



The Discharge of the Projectile. — Pilobolus Kleiriii and P. 

 longipes can both shoot their largest sporangia vertically upwards 

 to a maximum height just exceeding six feet and to a maximum 

 horizontal distance just exceeding eight feet. It is therefore evident 

 that the Pilobolus gun gives its projectile a high initial velocity. 



When a Pilobolus gun is fully developed and ready to discharge 

 its projectile (Fig. 18, p. 50), the wall of the sporangiophore, i.e. of 

 the basal reservoir, stipe, and subsporangial swelling, is greatly 



