CHAPTER XVII 



THE PATH OF THE SPORES BETWEEN THE GILLS, ETC!.— THE 

 SPORABOLA— APPENDIX ON THE MOTION OF A SPHERE IN A 

 VISCOUS MEDIUM 



By methods already explained, it has been shown that it is possible 



to determine by observation (1) the maximum horizontal distance 



to which a spore travels when it has been shot out horizontally 



from a basidium lying in the hymenium of a gill,^ and (2) the 



terminal vertical velocity with which the spore falls toward the 



earth.2 With a knowledge of those data, and assuming that the 



resistance of the air is proportional to the velocity, it is possible 



to calculate the initial velocity with which a spore is shot off its 



sterigma, and also to map out the trajectory described. 



The initial velocity with which a spore leaves its sterigma, 



when projected in a horizontal direction, may be calculated as 



follows : — 



Let V = the terminal vei-tical velocity, 



X = the maximum horizontal distance of projection, 

 H — the initial horizontal velocity, and 

 g = the acceleration due to gravity. 



It can be shown ^ that 



H=f. 



For spores of Amanitopsis vaginata, it has been observed that 

 X = 0'02 cm. and V = 0'5 cm. per second approximately, whence 



„ 981x0-02 .f. 

 ^= 0-5 =^^' 



i.e. the spores are projected in the horizontal direction from the 

 sterigmata with an initial velocity of a])])roximately 40 cm. per 



1 Method II., Chap. XL * Chap. XV. 



^ A note on the motion of a sphere in a viscous medium is given in the 



Appendix to this chapter for convenience of reference. 



184 



