THE UPPER-AIR SPORA 



Sticky slides were exposed by Colonel Charles A. Lindbergh in special 

 containers at about i,ooo metres altitude during a flight between Maine 

 and Denmark. Material trapped over Davis Strait and East Greenland 

 included algae, fragments of insects' wings, diatoms, and possibly sponge 

 spicules, volcanic ash, and glass. Fungus spores were tentatively identified 

 as belonging to: Macrosporium^ Cladosporium, Leptosphaeria^ Myco- 

 sp/iaerella, Trichotlieciiim^ Helicosporium, Uromyces, Camarosporium, and 

 VentKria. Some of these were abundant over Maine and Labrador but 

 diminished over Davis Strait, the ice-cap of Greenland, and Denmark 

 Strait (Meier, 1935, 1935^7). 



Flights over the United States at from 150 metres to 5,500 metres 

 showed a varied spore 'population' which usually decreased in both 

 numbers and varietN'' above 2,400 metres. \'iable spores of Pestahzzia 

 were caught above Washington at 5,500 metres on 22 March 1932. Other 

 genera recognized included: Acremonklla, Alternaria (Macrosporium), 

 Aspergillus, ChaeTomium, Cladosporium, Coniothyriimi, Dejnatium, Epi- 

 coccuniy Fumago, Fusarium, Helniinthosporium, Penicillium, Sclerotinia, 

 StachybotrySy Stemphylium, and Trichoderma (Meier et al, 1933)- 



After flights over the Caribbean Sea, Meier (1936) came to feel that 

 trade-winds might be important in disseminating microbes. Viable spores 

 were found at 800 to 1,200 km. from land; but after rain squalls, Petri 

 dishes sometimes remained sterile after exposure at 60-240 m. altitude a 

 few kilometres to the leeward of islands — so demonstrating that showers 

 remove spores from surface winds. 



Sugar-beet pollen was trapped on agar plates during flights over a 

 small sugar-beet seed-growing area of 900 acres in New Mexico. Viable 

 beet pollen, mixed with pine pollen and fungus spores, occurred up to 

 1,500 metres, which was the greatest height tested and the level of the 

 dust horizon (Meier & Artschwager, 1938). 



(ii) Vertical gradients. During an epidemic of wheat rust in Manitoba 

 in July and August 1930, Peturson (1931) trapped spores at different 

 altitudes in eight aeroplane ascents. The average numbers of spores 

 caught per square inch of trap surface (presumably with comparable 

 exposure times) were: 305 metres, 10,050 spores; 1,520 metres, 1,180 

 spores; 3,050 metres, 28 spores; and 4,260 metres, 11 spores. By substi- 

 tution in Schmidt's equation {see p. 132) we find A = 5-8 X lo"*, if 

 Vs = I cm. per sec. 



Hubert (1932) trapped spores during two flights at the time of an 

 epidemic of yellow rust of wheat at Halle in Germany. During the second 

 flight, for which data are more extensive, the numbers of spores trapped 

 per square centimetre per minute of exposure at various heights were : 

 30 metres and less, 1,418 spores; 400 metres, 683 spores; 600 metres, 

 336 spores; and 800 metres, 82 spores. Substitution in Schmidt's equation 

 gives A = 1-5 X 10^. 



Similar values for A were indicated when tree pollen was trapped over 



137 



