THE SPORABOLA 



185 



second. Since the maximum horizontal distance of projection 

 is 0'02 cm., it is clear that in travelling only this short distance 

 the horizontal velocity of a spore is reduced from 40 cm. per 

 second to zero. This will not seem surprising when the ratio 

 of the surface to the mass of the spore is taken into account. 



Since the spores are shot outwards horizontally, they describe 

 a curved trajectory in falling toward the earth. The trajectory 

 is a peculiar one. In future it will be referred to as the sporabola. 



It can be shown that the equation for the sporabola is 



01 



00*. 



where V = the terminal vertical velocity, 



X = the maximum horizontal distance of projection, 

 g = the acceleration due to gravity, 



t/ = the distance of a point on the sporabola below the highest point, and 

 z= the distance of a point on the sporabola from the vertical axis. 



Since V, X, and g are known, by assuming values for x correspond- 

 ing values for y 

 can be calculated 

 and the sporabola 

 plotted out. The 

 accom panying 

 figure represents 

 the sporabolas for 

 A manitopsis vagi- 

 nata and Psalliota 

 campestris (Fig. 

 64). 



The sporabola 

 is remarkable in 

 that the horizontal 

 part passes very 

 sharply into the 

 vertical part. The 



horizontal and Flo 64 _ The sporabolas of two spores shot out horizontally 

 Vertical motions from the hymenium. The spores, drawn to scale, are 



shown below. The scale is in centimetres. 



appear to be al- 

 most independent of one another. Direct inspection of the curve 



