68 RESEARCHES ON FUNGI 



discharged was observed to be : for P. Kleinii, 8 feet • 5 inch ; 

 and for P. lo7igipes, 8 feet 7-5 inches. 



Theoretically, if the resistance due to the air be neglected, a 

 gun can shoot a projectile twice as far horizontally as it can vertically. 

 If, therefore, a Pilobolus gun could shoot a projectile in a vacuum 

 to a height of 6 feet, it would be able to shoot it under the same 

 conditions to a maximum horizontal distance of 12 feet.^ In actu- 

 ality, however, the air offers a considerable resistance to the flight 

 of a projectile less than 1 mm. in diameter ; and it is on account 

 of air-resistance that P. Kleinii and P. longipes, which shoot their 

 sporangia to a maximum height of about 6 feet, shoot their sporangia 

 to a maximum horizontal distance of only about 8 feet instead of 

 12 feet.2 



Since the calculations just recorded were made, Pringsheim 

 and Czurda,3 from measurements made with the help of a pair of 

 rotating slotted discs, have calculated that the velocity of the pro- 

 jectiles of the Pilobolus used in their experiments, just after discharge, 

 is approximately 46 feet per second (14 metres per second). Using 

 the equation given on page 66, it can be calculated that, if 

 the air offered no resistance, the height to which a projectile having 

 an initial velocity of 46 feet per second would rise, if shot verti- 

 cally upwards, is 33 feet. Since my own observations show that 

 the strongest Pilobolus guns shoot their projectiles vertically upwards 

 to a height of only 6 feet, it is obvious that, assuming the correctness 

 of Pringsheim and Czurda's observations and calculations, the air 

 must offer a very considerable resistance to the flight of the Pilobolus 

 projectile. 



The Structure of the Sporangiophore and Sporangium illustrated 

 by Pilobolus Kleinii and P. longipes. — The sporangiophore of P. 

 Kleinii, like that of other Piloboli, consists of a basal swelling (which 

 differs from that of P. longipes in being bulbous instead of much 



1 Cf. these Researches, Vol. V, 1933, Fig. 163, p. 328. 



^ The smaller the projectile, the more nearly equal to the vertical range does 

 the horizontal range of the gun become. It is for this reason that the vertical 

 and horizontal ranges of a hymenomycetous basidium, which shoots away four 

 tiny basidiospores, are approximately equal. Cf. these Researches, Vol. I, 1909, 

 p. 186 and Fig. 65. 



3 E. G. Pringsheim and V. Czurda, loc. cit., pp. 879-882. 



