THE MICROBIOLOGY OF THE ATMOSPHERE 



The average of all samples gave a concentration of 7-5 cultivable organisms 

 per cubic metre and varied from none at 850 metres altitude in De- 

 cember to a maximum of 42 per cubic metre at 460 metres in October. 

 In general the concentration decreased with increasing height, but on 

 25 January there was a zone of high concentration at 900 to 1,200 metres 

 altitude. 



SPORES OF GREEN PLANTS IN THE LOWER TROPOSPHERE 



Using a glass-wool filtration apparatus, Overeem (1936, 1937) 

 sampled from aircraft over the Netherlands on six occasions extending 

 from July to October at heights of 100, 500, 1,000 and 2,000 metres. 

 Filter washings were inoculated to Pringsheim's culture solution for 

 green plants and kept in the light. From a total of about 28 cubic metres 

 of air she obtained the following cultures. Algae: Chlorococcum sp., 9; 

 Phormidium luridum var. nigrescens, Chlorella vulgaris^ Pleurococcus 

 vulgaris^ and Stichococcus bacilhiris, 3 each; Aphanocapsa sp., 2; Actin- 

 astrum sp., Stichococcus jninor^ and Hormidium fiaccidum^ i each. Moss: 

 Funaria hygrometrica^ 2 (from 500 and 1,000 metres). Fern: i (unidenti- 

 fied, from 500 metres). Total numbers at the various altitudes were in 

 the ratios 5 : 10 : 3 : 3 at 100, 500, 1,000 and 2,000 metres, respectively. 

 This work is of particular interest as one of the few demonstrations that 

 spores of green plants invade the troposphere in fiiir numbers and variety. 



McGiLL University Studies 



FLIGHTS OVER THE ARCTIC 



Extensive exploration of the upper air by aeroplane was initiated by 

 Polunin at McGill University, Montreal, in 1947, and continued until 

 1 95 1 with the co-operation of the Royal Canadian Air Force and the 

 United States Air Force. Flights during 1947-49 ^^'^^^ primarily directed 

 to the study of arctic conditions. 



In the summer of 1947 flights w^ere over the Northwest Territories 

 northwards to Cape Bathurst, then north-east from Cambridge Bay to 

 Victoria Island to beyond the region of the north magnetic pole and back, 

 and finally south-west from Cambridge Bay to Yellowknife and to Ed- 

 monton, Alberta. Petri dishes with nutrient medium, and also sticky 

 slides, were exposed from his planes by hand, mostly at about 1,500 

 metres altitude (Polunin et a I., 1947, 1948). There were small but meas- 

 urable concentrations of fungus spores, and the composition of the air- 

 spora appeared to depend on the origin and sometimes on the trajectory 

 of the air mass rather than upon the locality of sampling (Polunin, 1951, 

 1951a, and cf. 1954). The bacteria were identified as: gram-positive rods, 

 about 40 per cent (two thirds of which morphologically resembled 

 Corynebacterium), Micrococcus (23 per cent), Achromobacter or Flavo- 

 bacterium (17 per cent), spore-formers (4 per cent), and Sarcina (3 per 

 cent). Fungi identified in culture included Cladosporium (over 40 per cent 



140 



