RESEARCHES ON FUNGI 



basidiospores, mould spores, yeast cells, bacteria, or pollen grains, 

 is advantageous to the species concerned in at least two ways : 

 (1) it permits of these cells being produced in vast numbers so 

 that the chances that some of them will settle in favourable positions 

 is greatly increased and (2), being correlated with a very slow rate 

 of fall, it enables the wind to carry the cells relatively very long 

 distances before they settle, thus assisting the agent of dispersal. 

 In concluding this section, it may be pointed out that a spore or 



Comparative Rates of Fall of Thistle-down, Basidiospores, and 

 Bacteria in Still Air. 



bacterium, on being cast into the air, must, unless the air is abso- 

 lutely saturated with water vapour, dry up immediately. The 

 rapidity with which basidiospores dry up when they fall from 

 the hymenium of an agaric on to a slide placed beneath them 

 in a laboratory, is well known, and I have remarked upon it in 

 Volume I. 1 In ordinary unsaturated air, either in the laboratory or 

 in the open, the spores of Hymenomycetes dry up in a few seconds. 

 Doubtless, under similar conditions, Micrococci and Streptococci 

 dry up in less than one-tenth of a second. A spore or bacterium, 

 therefore, when floating in the air, must be thought of as existing 

 in a condition not of turgidity but of desiccation. 



1 Vol. i, 1909, p. 162. 



