1110 
at the same time, maintain higher concentrations of 
organisms in the surface layers; the presence of a 
discontinuity surface in the upper air will limit vertical 
transport in either direction resulting mm the concentra- 
tion of organisms above or below such a surface. There 
are several recorded instances of such biologic strati- 
fication. For example, Durham [8] has noted that abrupt 
spore ceilings are often marked by a cloud layer or by 
a visible haze line. He noted one instance in which a 
detached cloud of fungus spores, almost 100 per cent 
Alternaria, was encountered about 1000 feet above a 
visible 4000-ft haze line that marked the ceiling for 
ragweed and the ground cloud of other spores. An 
analysis of the meteorological conditions that existed 
near New Orleans on September 12, 1940 (the date and 
place of collection), might prove interesting, particu- 
larly if the source of the “cloud” of Alternaria could be 
identified. 
Nearly all investigators who have studied the vertical 
distribution of organisms in the atmosphere have noted 
the importance of thermal convection in increasing the 
populations at higher altitudes. Thermal convection 
over a region is a diurnal phenomenon and is usually at 
a maximum in the early afternoon; as a result, the 
maximum altitude populated by organisms should be 
highest at this time of day. Nearly all the data on 
insect populations verify this conclusion. 
In general, the horizontal transport of organisms will 
be determined by the general stream flow in the at- 
mosphere, but lateral mixing will transport the or- 
ganisms laterally away from the trajectories indicated 
in the general wind observations. In temperate lati- 
tudes, the greater transport will be from west to east 
and, considering the greater carrying power of polar 
air masses, from north to south. As an example of the 
latter, Durham [8] calls attention to a remarkable 
mold-spore shower that occurred October 6-8, 1937, 
over the eastern half of the United States. Durmg this 
period, extremely high slide counts of Alternaria and 
Hormodendrum were recorded at all collection pomts 
between southern Minnesota and Louisiana with some- 
what mereased counts in the tier of states between 
North Dakota and Texas. He presents a map of the 
area which shows, for each of the three days, the lime 
along which the concentration of the organisms was a 
maximum. The writer has referred to the synoptic 
charts for those dates and finds it interesting to discover 
that Durham’s lines of maximum spore concentration 
on each date coincide almost exactly with the daily 
positions of an extensive and rapidly-moving dry cold 
front. 
A number of investigators have attempted to describe 
mathematically the vertical and horizontal distribu- 
tions of organisms as functions of space or time but none 
appear to have been too successful. Wolfenbarger [88] 
has prepared regression formulas for the plots of a 
very large number of series of data on the spatial 
variations in organism counts; all are based on the form 
E=a-+ b(in2), or 
E=a-+ b(n 2) + c(1/2), 
BIOLOGICAL AND CHEMICAL METEOROLOGY 
where # is the calculated number or concentration of 
organisms, a is the position on the graph and 6 and c 
are factors determining the slope of the curve as in- 
fluenced by the logarithm or reciprocal of the distance 
x from the source. He presents the completed formulas 
for 251 separate plots of data. For example he finds, 
from one set of data, that the number of codling moths 
caught at a distance of x feet from an infested orchard 
can be given approximately by the expression: 
E = 5.2904 (log x) + 20114.0849 (1/x)—18.0628. 
Since the formulas nowhere take into account meteoro- 
logical conditions or other factors governing distri- 
bution, the writer fails to appreciate the great amount 
of effort that must have gone into their preparation. 
CONCLUDING REMARKS 
No attempt has been made in these pages to cover in 
detail the list of specific possibilities for research in the 
field, either from the standpoint of the biologist or of 
the meteorologist. The principal gaps in the research 
programs conducted by aerobiologists have been 
pointed out, and suggestions for general lines of re- 
search have been offered in the several sections. The 
writer hopes that the discussion will serve as an added 
stimulus toward future investigations in the field by 
both groups and that it will, in some measure, give 
guidance to the biologist. It is the problem of the 
biologist to develop certain and rapid methods for 
identifying the organisms with respect to type and 
place of origin; it will be the problem of the meteor- 
ologist to apply the results of the biological mvesti- 
gations to a study of the atmosphere. 
The author is indebted to Drs. B. EH. Proctor, E. C. 
Stakman, J. J. Christensen, R. P. Wodehouse, G. W. 
Keitt, and P. A. Glick for their assistance in locating 
recent materials on the subject of aerobiology and 
to Mrs. Marguerite Gleeck of the Air Weather Service, 
for her careful reading of the manuscript. The writer 
also wishes to acknowledge his extensive use of the 
volume Aerobiology, published by the American As- 
sociation for the Advancement of Science, as a source 
for biological information. 
REFERENCES 
No attempt is made here to cover the list of important 
papers concerned with aerobiological subjects. Care has been 
taken to include the more recent titles, those which, them- 
selves, contain extensive bibliographies, and all titles which 
have been specifically referred to in the text. A valuable bibhiog- 
raphy, which was published after this list of references was 
prepared, is that by Miss H. P. Kramer, ‘“‘Cumulative Anno- 
tated Bibliography on Aerobiology and Its Applications to 
Meteorology.”’ Meteor. Abstr. & Bibliogr., 1: 119-135 (1950). 
1. Berzanp, M. L., ‘“‘L’exploration biologique de 1’atmos- 
phére en avion, et |’emploi possible de cette méthode en 
météorologie.”’ La Météor., Ser. 3, No.1, pp. 28-35 (1936). 
2. Curster, K. §., ‘‘Airplane Spore Traps for Studying the 
Annual Migration of Wheat Rust.’? Proc. Okla. Acad. 
Sci., 19: 101-104 (1939). 
3. CuristeNnseN, J. J., ‘Long Distance Dissemination of 
