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,t and decreased with increas- 

 ing injliry 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- 

 lakable 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 

 11.) is much more rapid than the descent of that for wheat 

 (Diagram I.); that, in other words, the larger acreage of the 

 form'er 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 IL ) 

 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 

 fV)r grass in the worse infested neighborhoods, and in part the 

 breeding of chinch bugs in meadows where the wheat area was 

 very much reduced. 



•Table I. p. 13. fTable V. p. 19. JTable XI. p. 22. 



