THE SPECIFIC GRAVITY OF SPORES 157 



convection currents in the chamber, although not entirely absent, 

 appeared to be negligible. In the case of Coprinus plicatilis, ten 

 spores were carefully timed in falling through a field of 1-6 mm. 

 in width. On the average each spore took 2 mins. 57 sees, to 

 fall this distance. The velocity of the fall of the spores in water 

 was thus found to be 0*00090 cm. per second. The velocity of 

 fall of the spores in air was found by finding the time required 

 for them to fall vertically through a distance of 4-55 mm. from 

 pieces of gills placed in a small compressor cell. 1 The speed was 

 found to be 0-429 cm. per second. 



Putting v' = 0-0009, <y = 0'429, ^ = l-8xlO- 4 , and /*' = l-2x 10" 2 , 

 we get p, the specific gravity of the Coprinus spores, = 1-16. 



With Mushroom spores it was found that v' 0-00025 and 

 v = 0-13, whence p = 1-15. 



Both results are within 6 per cent, of those obtained by the 

 other method. The present method seems to me to be less 

 reliable than the first on account of its indirectness and the 

 assumptions involved. Stokes' Law was assumed to be true : the 

 spores were not spherical. Possibly the errors in estimating the 

 rates of fall of the spores in water are quite appreciable. Never- 

 theless, the result may be correct to within 10 per cent. 



If we take the results given by the heavy-fluid method to be 

 fairly reliable, we may conclude that the specific gravities of the 

 spores are as follows : for Coprinus plicatilis 1*21, for Psalliota 

 campestris 1*2, and for Amanitopsis vaginata 1*02. The spores 

 of the last-named species are much lighter than those of the other 

 two. This is probably due to the very large amount of oil which 

 the spores of Amanitopsis contain. The oil is certainly a very 

 light constituent of each cell, for, when a spore is falling in water, 

 the large oil mass, as seen with the horizontal microscope, occupies 

 the highest position possible. On account of the spores of 

 Amanitopsis vaginata having about the same specific gravity as 

 water, it was not found possible to measure the rate of their fall 

 in that medium. Their motion was so slow that even minute 

 convection currents proved to be a serious source of error in making 

 the measurements. 



1 Vide infra, Chap. XV. 



