Pollen [L] 



THE MICROBIOLOGY OF THE ATMOSPHERE 



Alternaria 



9 ^ 

 Cladosporiuw ^ 



--0-- 



Group A filiforms 

 Group B fusiforms 



--0-- 



Group C hyaline 

 unidentified 



75 



50 



25 



/ 



Noon 



\ 





/ / 

 / / 



/ -I 



Fig. 20. — Mean diurnal periodicity curves of thirteen spore-groups expressed as percentage 

 of the peak geometric mean concentration. (From Hirst trap records at Rothamsted Experi- 

 mental Station, summer 1952.) (The symbols 'L' and 'U' refer to corrections applied to 

 the data, based on wind-tunnel tests of the Hirst trap with Lycnpodiiim and Ustilago spores, 

 respectively.) (Reproduced by permission of J. M. Hirst from the Transactions of the 

 British Mycological Society, 1953.) 



(iii) The forenoon pattern. The hours after dawn, o6-oo to lo-oo hours, 

 bring an interlude, but at about lo-oo or i roo hours the forenoon pattern 

 is characterized by peak concentrations of a few crop-pathogenic fungi, 

 e.g. Polythrincium trifolii and Phytophthora infestans. 



118 



