TIIK SPOUAIJOLA 



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 



?/ = ■ 



>»,( 



x\_x ) 



X) XI 



when 



V = the terminal vertical velocity, 



X = the maximum horizontal distance of projection, 

 g = the acceleration due to gravity, 



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

 .'• = 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 p anying 

 figure represents 

 the sporabolas for 

 A manitopsisvagi- 

 / 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 

 vertical motions 

 appear to be al- 

 most independent of one another 



c 01 



ox 



r 



r 



Fig. 64. — The sporabolas of two spores shot out horizontally 

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

 shown below. The scale is in centimetres. 



Direct inspection of the curve 



