58 RESEARCHES ON FUNGI 



However rapidly the projectile may be travelling, on striking a 

 blade of grass or any other obstacle, it always sticks where it strikes. 

 Under natural conditions, Pilobolus guns are usually situated on 

 the dung of herbivorous animals in pastures, etc., in consequence 

 of which the projectiles usually land on, and adhere to, the 

 surrounding herbage. 



Development of the Pilobolus Gun and its Projectile. — In a 

 good natural culture of Pilobolus a crop of Pilobolus guns and 

 projectiles is produced daily for several days in succession. Each 

 crop takes about 24 hours for its development which culminates in 

 the discharge of the sporangia between 9 a.m. and early afternoon. 

 In the late afternoon a new crop can be seen beginning to develop. 



The successive development of the stipe, the sporangium, and 

 the subsporangial swelling of Pilobolus Kleinii is shown on a larger 

 scale in Fig. 23, while a series of successive stages in the develop- 

 ment of a diurnal crop of fruit-bodies of P. longipes, as affected by 

 external conditions, particularly light and darkness, is represented 

 diagrammatically on a smaller scale in Fig. 24. 



The primordia of a new crop of Pilobolus guns and projectiles 

 consist of much swollen cells which are filled with dense orange-red 

 protoplasm and look like little tubers. These primordia, the 

 trophocysts of Morini,^ are formed in the mycelium at the surface 

 of the substratum by mid-day (Fig. 24, A). During the afternoon, 

 each primordium puts out a coarse cylindrical hypha which grows 

 away from the substratum into the air (Fig. 23, A). The red 

 protoplasm of the primordium flows up into the hypha which thereby 

 becomes reddened in its turn, particularly at its free end just below 

 the apical growing-point (Fig. 12, a, p. 23). The primordium 

 becomes the basal swelling of the new sporangiophore and the 

 coarse hypha the stipe. From the first the young sporangiophore 

 is positively heliotropic, and from early afternoon to dark, as it 

 grows in length, it keeps its long axis parallel to the strongest 

 incident rays of light (Fig. 24, B and C). If, as happens in the 

 depth of winter, darkness supervenes before the sporangium begins 

 to develop, the sporangiophore continues to grow in length 

 orthotropically (Fig. 24, C and D). Toward evening, the end of 



^ Vide supra, p. 53. 



