ARTIFICIAL INFECTION—FIELD EXPERIMENTS. 27 
plots of shade-giving, low-statured plants were set out in certain 
badly infested wheat fields. Shading experiments of a different na- 
ture were tried in cornfields, but these will be discussed in another 
place. 
The plots were set out to beans or cowpeas, as the case might be 
(the former proving the better), and were 50 feet square. A row of 
beans a foot wide formed the four sides of the square, and four rows, 
each a foot wide, were planted across the square, 10 feet apart, so 
that they would intersect the wheat rows at right angles. The ap- 
pearance of each plot when finished was that of a gridiron. 
The original purpose was to provide such shade that chinch bugs 
traveling along the wheat rows would encounter the shade and the 
moisture conditions of the bean rows. The beans were planted 
thickly, so that when the plants grew to 8 or 10 inches in height the 
ground beneath them was moist when that elsewhere would be dry. 
It was hoped that the wheat would come into close connection with 
the bean rows, but this was not always the case. It was hoped, also, 
that the bugs would seek the shade, and thereby enter conditions 
which would favor the development of Sporotrichum. It was found, 
however, that the bugs did not collect under the beans to any extent, 
nor did they appear to pass across the rows except 1n a few instances. 
Hence the infection sown among the beans, or cowpeas, failed to gain 
a favorable opportunity to come into contact with the bugs. While 
as a shading experiment the bean plots were of no value, they served 
a most excellent use as areas of infection or centers of infection. As 
they were laid out directly in the wheat they contained chinch bugs 
in as great numbers as the wheat outside them. Fungus was sown 
in them in large amounts, so that one might expect one of two results: 
(1) The chinch bugs inclosed by the plots showing greater mortality 
by Sporotrichum; (2) the plots becoming centers of field infection, 
with the greatest effect seen nearest the plots themselves. In most 
instances the experimental areas exhibited spontaneous outbreaks of 
Sporotrichum, and, with the fungus sown artificially, the plots con- 
tained an extensive amount of infectious material. In each experi- 
mental field, where a 50 by 50 foot experimental area was inoculated 
with fungus spores, a check area, or plot, similar in every way, was 
laid out from 100 to 200 yards distant. By comparing the two plots 
the effect of the artificial infection could be judged better. 
The spread of the disease, if any occurred, was watched not only 
in the experimental areas but in other parts of the field and in fields 
at distances from a fourth of a mile to several miles. 
Artificial infection—Localities in which field experiments were 
conducted.—In the selection of fields for artificial infection the first 
prerequisite was the presence of large numbers of chinch bugs, since 
a contagion of any kind spreads faster, other things being equal, 
