THE UPPER-AIR SPORA 



of the total), Sporormia^Pulhdaria, VerticiUium, Penicilliuni, yeasts, Phyllo- 

 sticta, Leptosphaeria, Alternaria, Stemphylium, Chaetomium, Pestallozia, 

 and Streptomjces {?-a.Ay et al., 1948; Pady, 1951; Polunin, 1951, i95irt). 



The sticky slides exposed during flights over the Northwest Terri- 

 tories showed small concentrations of angiosperm and g^'mnosperm pollen, 

 spores of pteridophytes and bryophytes, Alternaria, and Helniinthosporiutn 

 sativum, totalling about i per cubic metre. Uredospores of the cereal 

 rusts Piiccinia graminis and P. glumarum occurred in small numbers 

 (except in the most northerly flight, though a few were found north of 

 the Arctic Circle); their concentration rose to about 12 per cubic metre 

 over northern Alberta, w here there was also a smut concentration of about 

 6 per cubic metre (Pady et al, 1950; Polunin, 195 1«). 



In further flights over the Arctic the McGill workers attempted more 

 elaborate sampling methods to eliminate possible contamination from 

 within the aircraft, which could have increased the counts in the first 

 two or three exposures of the earlier flights. In September 1948, Polunin 

 flew over the Geographical North Pole in a B-29 aircraft fitted with a 

 breech loading tube to hold a Petri dish projecting 30 cm. forward of the 

 nose. Before exposure the interior of the Petri dish was coated with a 

 silicone grease; and after returning to base, the dish was poured with 

 molten agar and incubated. 



Immediately over the North Pole in late summer at 920 metres neither 

 bacteria nor fungi were caught. However, at greater heights over the Pole 

 and at other high latitudes, some Petri dishes caught nothing, while others, 

 exposed at altitudes up to 6,770 metres, grew a few colonies of bacteria or 

 moulds; no Actinomycetes were found (Polunin, 1951; Polunin & Kelly, 

 1952). Thus microbes appear to be present, though irregularly distri- 

 buted, even over the Poles. 



During a flight over the Geographical North Pole under winter con- 

 ditions in March 1949, the McGill workers used three kinds of samplers: 

 (i) siHconed slides exposed in the tube forward of the nose of the 

 plane ; (2) an electrostatic sampler installed in a box through which a slow 

 stream of air was passed ; and (3) a filter tube packed with glass-wool and 

 lens-paper. The electrostatic sampler and filters indicated a viable 

 concentration of 26 bacteria + yeasts and i-6 fungi per cubic metre in 

 some ver}' high latitudes. The authors concluded that the air over the 

 Pole and its environs is nearly sterile and that it is of very mixed origin. 

 Here again there was evidence that the origin of an air-mass is more im- 

 portant than the localit}' of sampling (Polunin, 195 1, 195 1«, 1954; Polunin 

 & Kelly, 1952). 



The results of further arctic and sub-arctic flights are reported in 

 detail by Pady & Kelly (1953) and Pady & Kapica (1953). On one from 

 Winnipeg via Churchill to Baker Lake in the Northwest Territories at an 

 altitude of about 1,000 metres, using the G.E. Electrostatic sampler, 

 cultures averaged: bacteria 10, and fungi 25, per cubic metre. Bacteria 



141 



