29 
DISCUSSION OF DIAGRAMS. 
Diagram I. While the line representing the wheat area on Dia¬ 
gram I. is extremely irregular, the second and third points especially 
(derived respectively from only six and seven townships) being 
perhaps too high, its general tendency downward is unmistakable, 
as shown by the curved line of average direction. The declining 
slope of this line expresses the fact that in Southern Illinois the 
wheat area diminished, on the whole, with increasing chinch-bug 
injury to all the crops (including wheat itself), this diminution 
not affecting, however, the slighter grades of injury, where a rapid 
increase of the wheat area is apparent. Recalling the fact that 
the wheat acreage increased with the corn injury,* remained con¬ 
stant with increasing injury to grass,f and decreased with increas¬ 
ing injury to wheat and oats,J we see that this means that the 
diminishing acreage of the small-grain table overcomes, when 
combined with it, the increasing acreage of that for corn. The 
full significance of this exhibit can be best set forth in compari¬ 
son with the data for oats, presented by line B on the next dia¬ 
gram. 
“Diagram II. This most interesting diagram shows with unmis¬ 
takable clearness the relation of oats culture to chinch-bug injury in 
Southern Illinois last year. The rapid and fairly uniform ascent 
from about 1,200 acres per township for the lower grades of loss to 
3,000 acres for the higher, represents probably the most important 
fact brought out by this whole study; viz., the relation of the oats 
area to chinch-bug increase where this has already reached an ex¬ 
cessive pitch. The attentive reader will not have failed to notice, 
however, that the oats line begins with a downward slope, in oppo¬ 
sition to the first part of that for wheat,—a hint at a point which 
we shall see fully brought out in the discussion of the situation 
in Central Illinois. 
We observe next that the ascent of the line for oats (Diagram 
II.) is much more rapid than the descent of that for wheat 
(Diagram I.); that, in other words, the larger acreage of the 
former crop does not simply replace the diminished area of the 
latter, but does this and much more. If, as already intimated, 
this difference is taken as an indication of the extent to which 
the chinch bug bred in oats last year, it will be very difficult 
to show that this interpretation is erroneous. 
The meaning of the lines for grass, (marked A on Diagram IT ) 
is much the same as that of the lines for oats, just treated. An 
average upward slope of about the same pitch as the preceding, 
shows, as in the other case, in part the abandonment of wheat 
for grass in the worse infested neighborhoods, and in part the 
breeding of chinch bugs in meadows whore the wheat area was 
very much reduced. 
•Table I. p. 13. fTable V. p. 19. JTable XI. p. 22. 
