THE MICROBIOLOGY OF THE ATMOSPHERE 



TABLE XIII 



OBSERVED VALUES OF p AND Vg FOR Lycopodmil SPORES ON HORIZONTAL 



microscope slide in wind-tunnel (turbulent and streamlined 



conditions) 



Wind-speed cm. /sec. 



950 



575 



320 



170 



50 



Loss by Deposition from Spore-cloud 



To judge from outdoor values of p and Vg, a spore-cloud liberated 

 near ground-level must lose an important fraction of its original number 

 by deposition on the ground in the early stages of its diffusion. Relevant 

 field measurements are incomplete, but we have attempted to make 

 minimum estimates of ground deposition from the experiments of 

 Stepanov (1935) and Gregory, Longhurst & Sreeramulu {unpublished), 

 where Qp is known and where deposition was measured at several dis- 

 tances along lines radiating from the point of dispersion. Each experi- 

 mental value was plotted to scale on graph paper, points were joined, and 

 the total number of spores deposited within the area sampled was esti- 

 mated by integrating areas under the curves (Table XIV). It is clear that 

 spores must also have been deposited on each side of the area sampled, 



TABLE XIV 



percentage of total spores (Q_o) liberated near ground-level THAT 

 WERE ESTIMATED TO HAVE BEEN DEPOSITED ON GROUND IN OPEN-AIR TESTS 



Estimate of percentage 



of spores recovered 



on test area 



