6o4 
Journal of Agricultural Research 
Vol. XXIV, No 7 
The real question, however, is not whether a great many spores are 
in the upper air, but whether they still are viable when they reach the 
surface of the earth. The difficulty of determining this conclusively is 
quite apparent. Germination tests were made, but some of them were 
inconclusive. The spores were embedded in vaseline, and when they 
were transferred to water they apparently did not imbibe much of it on 
account of the presence of the vaseline on the exospore. However, 
Altemaria spores which* had been caught at 3,000, 4,000, 8,000, and 
10,500 feet, respectively, germinated quite readily. 
None of the urediniospores of Puccinia graminis germinated in 1921, 
but many of the tests were made too long after the spores were caught. 
In 1922, many more tests were made, and it was found ^at urediniospores 
germinated readily when caught at altitudes up to 7,000 feet. No tests 
were m^de on spores which had been caught at higher elevations. In one 
test, 64 per cent of the urediniospores germinated on a slide which had 
been exposed at 2,000 feet. The altitude at which the spores were caught 
apparently had little or no effect upon their viability. It seems quite 
likely, therefore, that urediniospores might be carried for long distances 
in the air and still retain their power to germinate. Germination tests 
were made of the spores on 24 diflFerent slides, and an average of 11.2 
per cent of the urediniospores germinated. Considering the fact that the 
spores often were partially embedded in vaseline or glycerine jelly, a 
surprisingly large percentage germinated. A few aeciospores which had 
been caught at an elevation of 1,000 feet also germinated. Many of the 
other kinds of spores also germinated very readily. 
GENERAL DISCUSSION 
The results of these preliminary experiments indicate that large 
numbers of spores and pollen grains are carried several thousand feet 
above the surface of the earth during the growing season. Probably 
they are carried long distances by the upper air currents, the direction 
and velocity of which are quite different from those near the surface. 
If the spores retain their viability, as some of them quite probably do, 
it is conceivable that a local epidemic might occur in one locality as a 
result of the blowing in of spores from an infection center in another 
distant locality. It would be particularly desirable to know more about 
the dissemination of the spores of those pathogens which often seem to 
be .disseminated over wide areas in some almost miraculous manner, 
such for example, as Phytophthora infestans and various rust fungi. 
Attempts were made in 1922 to get data regarding the spread of 
black stem rust. Slides were exposed on airplanes in Nebraska, Kansas, 
and Oklahoma, before stem rust had developed in those States but 
when it was already present in Texas. No spores were caught, however, 
until rust began to develop near the area in which flights were made. 
Flights were made from Fort Sill, Okla., toward Denison, Tex., when 
there was a considerable amount of rust near Denison but none in 
Oklahoma. It was quite clear that the number of* spores in the air 
decreased rather rapidly as the distance from the rusted area increased. 
The distance to which spores may be carried undoubtedly depends on 
many factors, and no final conclusions can be drawn from a limited 
number of observations. Certainly aeciospores and urediniospores are 
carried up as high as 10,000 feet, and more, above the surface of the 
earth. Unless they are brought down by rain or some other agency, 
