34 o RESEARCHES ON FUNGI 



pressure of the membrane on the projectile, we may assume that 

 the membrane at the moment of complete eversion has a velocity 

 of about 30 feet per second. The membrane starts from rest and 

 its base is raised through a distance of about 3 mm. Now if a body 

 starts from rest and travels for t seconds, finishing with a velocity of 

 v feet per second, its average velocity is \ v during this time and 



s — I vt 



where s is the distance travelled over. Applying this equation to 



30 

 the problem in hand, we have s = 3 mm. = — — - feet, v = 30 feet 

 r 3048 



per second, and t is the time taken for the eversion of the membrane. 



Therefore 



30 2 1 



t = x - = second. 



3048 30 1524 



Thus we see that the time taken for the discharge of our Sphaero- 

 bolus gun, i.e. for the eversion of the inner membrane, is only about 

 one-fifteen-hundredth part of one second. No wonder, therefore, 

 that the eye cannot observe the eversion movement. 



If the projectile were shot upwards to a maximum height of 

 7 feet instead of 14- 5 feet so that its initial velocity were only about 

 21 feet per second instead of about 30 feet per second, the time 

 taken for the eversion of the inner membrane would be increased 

 from about one-fifteen-hundredth of a second to about one- 

 thousandth of a second. Even so, the eversion movement is a very 

 sudden one and it is therefore not surprising that, on actually 

 watching Sphaerobolus guns which shot their projectiles to a 

 measured height of 6-7 feet, I was not able to perceive the inner 

 membrane become everted or the projectile leave the gun. 



(4) Function of the air-spaces between the outer and inner peridial 

 teeth. As already mentioned in a previous Section, after a fruit- 

 body has opened stellately the inner eversible peridial membrane 

 separates slightly from the outer non-eversible peridial membrane, 

 except at the tips of the teeth, so that a shallow concavo-convex 

 cavity filled with air is formed between the two membranes, as 

 shown in Fig. 161, B (p. 316). Since the separation of the inner 

 and outer membranes extends to the teeth, excepting their tips, 



