THEPILOBOLUS GUN AND ITS PROJECTILE 67 



and s = the vertical height to which a projectile is discharged when 

 shot vertically upwards, neglecting the resistance offered by the air 

 it can be calculated that a Pilobolus projectile, if shot vertically 

 upwards to a maximum height of 6 feet, has an initial velocity of 

 19-6 feet per second. 



.When the resistance offered by the air to the flight of a Pilobolus 

 projectile is taken into account, it is clear that the projectiles of 

 P. Kleinii and of P. longipes which were shot up to a height of 

 6 feet 0-5 inch must have had an initial velocity which exceeded 

 20 feet per second. 



Employing the equation : 



s = Igt^ 

 where s = the vertical distance of rise or fall, g = the acceleration 

 due to gravity, and t = the time of rise or fall in seconds, neglecting 

 the resistance offered by the air it can be calculated that, when a body 

 is shot up from rest to a height of 6 feet so that it falls back again 

 to where it started from, the total time of rise and fall = 2t = 2 x 

 0-61 =1-22 seconds. Because of the resistance of the air, the 

 projectiles of P. Kleinii and of P. longipes which rise to a height of 

 6 feet and then tall to earth must take upwards of 1-22 seconds to 

 complete their movement. 



The horizontal range of the guns of P. Kleinii and of P. longipes 

 was investigated by putting the culture dish in a special experi- 

 mental chamber 12 feet long and 3 feet wide built of beaver-board 

 about a window in the laboratory. The culture dish was placed 

 on the floor under the window and tilted to an angle of 45°-50° 

 from the horizontal and light from an upper window-pane was re- 

 flected to it at an angle of about 40°-45° from the vertical by means 

 of a vertical mirror hanging four feet above the floor. The chamber 

 was painted black inside and its air was moistened by spraying it 

 with water. The floor of the chamber was covered with sheets of 

 white paper to receive any sporangia which might fall on it. The 

 sporangiophores, in consequence of their heliotropism, became 

 directed toward the light at an angle of 40°-45° with the horizontal 

 before they began to discharge their sporangia. 



In a series of experiments made in the chamber just described, 

 the maximum horizontal distance to which any sporangium was 



