IX 



THE AIR-SPORA NEAR THE EARTH'S SURFACE 



Ultimately we hope to attain an undistorted picture of the ambient 

 outdoor air-spora. All air-sampling methods are more or less selective. 

 This chapter deals with the concentrations of microbes in suspension in 

 air near the ground — that is, within the laminar and turbulent boundary 

 layers ordinarily inhabited by man, animals, and plants. The account is 

 based on the limited amount of information obtained by volumetric 

 air sampling with reasonably efficient apparatus. No attempt will be made 

 to summarize the extensive results from gravity-slide and Petri dish 

 traps, as these are already covered by excellent summaries by Feinberg 

 et al. (1946), Maunsell (1954), Werff (1958), and others, though the 

 results of long-term sampling with such surface traps will be drawn 

 upon for supplementary information when required. 



Composition of the Air-Spora 



Some 1,200 species of bacteria and actinomycetes are recognized. Other 

 spore-producing plants include perhaps 40,000 species of fungi, numerous 

 mosses, liverworts, ferns and their 'allies', and more than 100,000 species 

 of pollen-producing flowering plants of which about 10 per cent are 

 wind-pollinated. (Of the Protozoa able to enter the air-spora, our informa- 

 tion is very meagre and unsystematic.) 



A taxonomist, having in mind the twenty-five volumes of Saccardo's 

 Sylloge Fungoriim or the many volumes and supplements of Index 

 Kewensis, may wonder what useful statements can possibly be made about 

 the air-spora where most of the fungus or other plant bodies whose 

 characters could aid identification are lacking. Fortunately, as a cursory 

 microscopic examination of the deposit from an impactor trap shows, 

 the potentially airborne organisms are not all equally common in the air. 

 One sample is normally dominated by one or two types of spore, with 

 several other types in fair abundance and many more encountered in 

 ones and twos only. The frequency distribution of individuals of different 

 species in an air-spora resembles the series of the logarithmic and log- 

 normal types discussed by Fisher et al. (1943), and by Williams (1947, 

 i960). Investigation will doubtless show that different air-sporas have 

 different 'diversities'. 



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