178 RESEARCHES ON FUNGI 



of the centre of the (•loud. They came to the conclusion that for lycopodiuin 

 spores tlie formula gives velocities 50 per cent, in excess of those (jbserved. 



My method for testing Stokes' formula appears to have various advantages 

 over that used by Zeleny and M'Keehan for the following reasons. Amani- 

 to2)sis spores have smooth walls and are practically truly spherical, whereas 

 lycopodium spores have sculptured walls and are four-sided. Amanitopsis 

 spores have a diameter oidy about one-third as great as lycopodium spores. 

 In the tube method convection currents cannot be eliminated, and it must 

 surely be somewhat difficult to decide the exact centre of the si)ore clouds. 

 By my method of using a very small chamber, the difficulty of convection 

 currents was reduced so as to be negligil)le, and the velocities of the individual 

 spores could be measured with consideral)le accuracy. Amanitopsis spores are 

 liberated spontaneously by the fungus, W'hercas lycopodium powder requires to 

 be set in motion by artificial means. ^ 



^ The substance of this Appendix is contained in a letter to Nature on " The 

 Rate of Fall of Fungus Spores in Air," April 14, 1909. 



