14 



for discussion, we observe at once that the figures for wheat in- 

 crease regularly from 1,311 acres per township, where the injury 

 was none, to 3,189 acres, where the loss was nearly complete. An 

 inspection of the columns for the other crops shows us that here 

 the grass areas remain about the same, neither rising nor falling-, 

 if we take the list together; but that the figures for corn and oats 

 clearly show a tendency the reverse of that observed in Southern 

 Illinois; for while the successive numbers run somewhat irregu- 

 larly, the whole series is clearly a descending one. Certainly, 

 therefore, we must conclude that in this great territory increased 

 injury to corn goes along with an increased acreage in wheat, as 

 in Southern Illinois; but as this is also attended by a decreased 

 acreage of corn and oats, it remains for us to determine whether 

 the greater damage to corn may not all be connected with this 

 latter fact, — may not be due simply to a more concentrated attack 

 in the smaller corn area. A simple calculation demonstrates, how- 

 ever, that the average increase in the series of figures for wheat, 

 (24 per cent.) is nearly five times as great as the average inverse 

 ratio in the figures for corn (5 per cent.) and six times as great 

 as for oats (4 per cent.). In other words, as the wheat area in- 

 creases many times faster than the corn area decreases, the in- 

 creased wheat area must be held to have much more to do with 

 the greater chinch-bug injury than does the decreased corn area. 



From this table we seem to learn that in the beginning of a 

 chinch-bug outbreak the area in wheat has much more to do with 

 the continuance and increase of injury than that in any other 

 crop; that the acreage of oats, corn, and grass has then, in fact, 

 no apparent influence, where wheat is also raised. 



The separate tables for the three subdivisions of Central Illinois 

 simply show in each the same state of facts apparent in the more 

 general exhibit, and are consequently not here reproduced. 



Table III. 



Northern Illinois, 224 Towns. Injury to Corn, 1887, compared 

 with Crop Areas for the Same Year. 



Degree of Injury. 



No. of 



TpB. 



Wheat. 



Barley. 



Rye. 



Oats. 



Corn. 



Graes. 





147 



•.m 



152 



376 



3,119 



4,628 



8,173 



Little 



48 



338 



165 



427 



3,199 



4,734 



7,976 





10 



324 



186 



840 



2,952 



8,786 



7,360 





16 



335 



165 



251 



3,169 



4,569 



6,957 



Great 



2 



431 



9 



368 



3,116 



5,066 



9,632 







213 



10 



14 



445 



1,020 



2, 626 



As is sufficiently evident from Table III., reports from Northern 

 Illinois can scarcely be used in this branch of our discussion, 

 both chinch-bug injury to corn, and the area in wheat being of 

 so little importance that wliatever slight effect one may have had 

 upon the otlier, is completely lost to view in the presence of other 

 causes of variation. Only the four minor grades of the scale of 



