THE AIR-SPORA NEAR THE EARTHS SURFACE 



north coast of Ellesmere Island and, in 1955, for the exposure of sticky 

 shdes (Barghoorn, i960) and Petri dishes of nutrient media (Polunin 

 et al. i960; Prince & Bakanauskas, i960) on Ice-Island T-3 when it was 

 floating in the North Polar Basin at about 83°N. Here again the air-spora 

 was found to be very sparse compared with middle latitudes, but it 

 included pollen grains which, in some instances, were indicative of long- 

 range transportation (cf. Barghoorn, i960, p. 91, despite p. 88). From the 

 T-3 exposures a small number of slow-growing fungus isolates (all 

 identified as PeniciUiiim viridicatum) and more of Actinomycetes were 

 obtained, but none of bacteria. 



The Origin of the Air-Spora 



There is no reason to doubt the conclusion of Miquel and of Proctor 

 (1935) that most bacteria of the air originate from the soil, or from the 

 oceans (ZoBell, 1946). But it is doubtful whether the soil makes any sub- 

 stantial contribution to the fungus spore content of the atmosphere, as has 

 been argued by some writers. It seems more likely that this air-spora is 

 derived predominantly either from moulds, plant parasites, and other 

 fungi growing on vegetation, or from surface-growing fungi equipped 

 with explosive mechanisms which project their spores into the freely- 

 moving turbulent air layer. In the soil, bacteria, Penicillia, and Aspergilli 

 predominate; but Cladosporium predominates in the air, seconded by 

 basidiospores. Similarity between the soil- and air-sporas results mainly 

 from the soil being the ultimate 'sink' to which most of the spores of the 

 air are destined. 



Much of the air-spora comes from wild vegetation. Industry pollutes 

 the atmosphere mainly with inorganic particles and gases. It is not 

 generally appreciated, however, that agricultural practices may pollute 

 the air with plant pathogens and with respiratory allergens on a large scale. 

 Even such small operations as mowing grass may cause a local increase 

 in the Cladosporium content of the air by a factor of 20 times, as I have 

 found in recent tests (and cf. Sreeramulu, 1958). 



For microbes to get into the air in the high concentrations observed 

 at peak seasons, a take-off mechanism is necessary. However, the most 

 unlikely organisms occasionally get into the air. Siang (1949) isolated one 

 colony of the aquatic phycomycete, Hypochytrium catenoides, from air on a 

 roof at McGill University, Montreal, Canada. Probably almost every kind 

 of microbe would be found if sampling were continued long enough. 



From recent work on the air-spora near the ground, we learn that its 

 composition and concentration often fluctuate enormously — sometimes 

 w ithin quite short time-intervals. The significance of this for plant path- 

 ology and plant breeding is obvious. Some constituents, such as the grass 

 pollens, are important in respiratory allergy (the volume of air inhaled by 

 the human lung is of the order of i cubic metre per hour). In the course 

 I 129 



