6 oo 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
for the operator, seated in the passenger cockpit of the plane, to expose 
the slide by hand for the desired length of time and then return it to the 
slide box in which it had been carried. Another method consisted in 
placing inside of a bottle a microscope slide attached to a wooden paddle, 
the upper part of which extended through a hole in the cork of the bottle 
and served as a handle. After the slide had been exposed it was again 
placed in the bottle. This obviated the necessity of opening the slide 
box in order to remove or insert a slide, but was rather cumbersome, as 
it was necessary to carry as many bottles as there were slides to be 
exposed. 
A third method was to expose the slides in a mechanical spore trap. 
Several types of trap were used, but one devised by Mr. George was the 
most satisfactory. This was made with six compartments, each con¬ 
taining a slide. It was fastened to the wing struts of the plane and was 
provided with a wire control which was operated by the observer in the 
cockpit. One pull on the wire opened the first compartment and exposed 
slide No. i; a second pull closed this compartment and terminated the 
exposure of the slide. The other compartments were opened and closed 
in the same manner. (PI. 2.) By this method slides could be exposed, 
one at a time, for the desired lengtn of time, at various altitudes, and at 
widely separated points. 
Flights were made in southern Texas during the latter part of April 
and during May, at St. Paul on June 25, and between Omaha, Nebr., 
and Cheyenne, Wyo., in July, 1921. The exposed slides were sent 
immediately in tight boxes to St. Paul, where spore counts were made. 
RFSUbTS 
Some typical results of exposing slides are summarized in Tables I 
and II. It is evident that tnere are many fungous spores at altitudes 
as high as 11,000 feet above the surface of the earth. In examining the 
slides special attention was given to rust spores. However, a great 
many spores of many other kinds of fungi, as well as conidiophores, 
numerous pollen grains, glumes of grasses, and some small insects also 
were caught on the slides. 
It was practically impossible to identify many of the spores definitely. 
It was certain, however, that there were many spores of Puccinia, 
Altemaria, Helminthosporium, Cladosporium, Cephalothecium, Ustilago, 
Tilletia, and Scolecotrichum. (PI. i.) Spores of Altemaria were by far 
the most numerous, and not infrequently they were found adhering in 
characteristic chains. Chains of Cladosporium spores also often were 
found on the slides. On some of the slides there were large clumps of 
smut spores, there being approximately 60 in one of the largest clumps. 
Urediniospores were caught more commonly than any of the other spore 
forms of rust fungi, although teliospores were not uncommon, and, in 
1922, aeciospores also were caught. On one slide there was a spore of 
what appeared to be Ustilago zeae with a promycelium and about 20 
sporidia still attached. It is possible that this spore may have germinated 
in the vaseline. This seems quite unlikely, however, as there was no 
•indication whatever that any of the other spores had germinated, and 
it seemed more probable, therefore, that the spore with its promycelium 
and attached sporidia was carried up into the air after it had germinated. 
