564 RESEARCHES ON FUNGI 



gales in spring and autumn in Manitoba I have sometimes noticed 

 that the air becomes distinctly hazy from the vast amount of 

 extremely fine dust which has been picked up from the ground. 

 Under such conditions the organic constitutents of the suspended 

 dust are considerable. In the course of a series of experiments 

 carried out every week throughout a whole year to determine the 

 number of bacteria in the air of Winnipeg, C. W. Lowe and the 

 author 1 found that during high gales as many as 8,000 bacteria 

 were falling on each square foot of ground per minute. Now since 

 these gales persisted for about 24 hours each, the air being dust- 

 laden all the time, it is clear that after each gale, as the dust in the 

 air settles, every square foot of earth must receive a vast number 

 of new bacteria which have been transported by the wind for a 

 considerable distance. Unfortunately, we have but few data con- 

 cerning the dispersion of uredospores. However, the number of 

 uredospores which are caught up by high winds from certain wheat 

 fields is doubtless mconceivable ; and, if we could only follow these 

 uredospores and map out their places of lodgment, we should 

 probably sometimes find them dispersed over hundreds of square 

 miles stretching outwards in the direction of the prevailing wind 

 and away from the source of the spores. The uredospores would 

 settle down after a gale like the bacteria already spoken of, although 

 doubtless in much smaller numbers. 



In support of the theory of long-distance wind-dispersal as a 

 factor in outbreaks of the Black Stem Rust Disease of wheat, may 

 be cited the observations of Stakman, Henry, Curran, and Christo- 

 pher, made in the United States with the help of aeroplanes.^ In 

 the spring and summer of 1921, spore-traps (vaselined glass slides) 

 were exposed on aeroplanes in the Mississippi Valley at various 

 places and at various altitudes ; and many spores of pathogenic 

 fungi, as weU as conidiophores, poUen grains, glumes of grasses, 

 and small insects were caught. Spores and pollen grains were 



1 A H. R. Buller and C. W. Lowe, " Upon the Number of Micro-organisms in 

 the Air of Winnipeg," Trans. Roy. Soc. of Canada, Third series, vol. iv, section iv, 

 1911, pp. 51, 53, 55 ; also Plates I and II. 



2 E C Stakman, A. W. Henry, G. C. Curran and W. N. Christopher, Spores 

 in the Upper Air," Journal of Agricultural Research, vol. xxiv, 1923, pp. 599-606, 

 Plates I and II. 



