THE RATE OF FALL OF SPORES 



175 



to show the speed of fall of the spores at a certain distance from 

 the gills in the unsaturated air of the chamber. If V be the 

 velocity of a spore when fully expanded by osmotic pressure, 

 i.e. just after liberation, and V be the velocity of the same spore 

 when it has dried up, then the velocities given in the Table lie 

 between V and V. The value of V, as farther experiments have 

 shown, may be as much as 3V'. It will doubtless be different 

 for each species, but it is evident, from results given in the 

 Tables in the next chapter, that up to 60 per cent, should be 

 added on to the velocities given in the present Table in order 

 to obtain approximately the true rate of fall of the fully turgid 

 spores of which the dimensions are given. On the other hand, 

 if one wishes to calculate the velocity of the spores when dried 

 up, as they must often be in nature within one or a few minutes 

 of leaving the fruit-body, one must subtract up to GO per cent, 

 of the velocities determined. 



It was found possible to measure the rates of fall of individual 

 spores over longer distances than 4*55 mm. in the following 

 manner. A field just below the gills in the compressor cell was 

 focussed with the horizontal microscope. When a spore crossed 

 the upper line, a drum contact was made by depressing the knob 



