IVZ TKANSACTIONS OF THE ILLINOIS 



per cent. The damage to the picked fruit stands at a ratio of 

 twenty-one per cent, as compared with seventy-three per cent, on tlie 

 other two trees, a difference of fifty-two per cent. Taking all the 

 apples from these trees together, and comparing with the entire crop 

 of the check trees (last column, Diagram VII), assuming, as we evi- 

 dently have a right to do, that as great a portion of the fruit on the 

 experimental trees would have been destroyed as on the check trees 

 if the former had not been sprayed, we shall find that of the apples 

 thus exposed to damage by the codling moth almost exactly seventy 

 per cent, have been saved by our treatment. Or, taking the picked 

 and fallen apples separately, and making in the ratios exhibited by 

 our diagram certain mathematical corrections, without which our 

 computation will be misleading,* we find that eighty-six per cent of 

 the apples which would have fallen from the trees on account of 

 damage by the codling moth have been preserved to ripening; and 

 that the ratio of damage to the picked fruit on the poisoned trees is 

 only forty-tw^o per cent, that on the others. 



It will be readily understood that the ratio of injury in the fal- 

 len apples is so much less in the beginning of the season than later, 

 because in spring the tree casts its aborted fruit, Avhether this is in- 

 jured by insects or not. When this blasted surplus has been mostly 



♦Ratios are comparable, oi course, only when reckoned on the same base. For the check 

 trees the ratios of damage to the fallen apples were calculated on the total number fallen, and 

 for the picked apples the f'asis of the reckoning was the number remaining on the trees at the 

 end of the season. Since the treatment of the experimental trees kept from falling a certain 

 number of the apples which would otherwise have fallen, it is evident that ratios computed on 

 the fallen and picked apples on these trees are not comparable, without correction, with those 

 obtained from the checks. The number of fallen apples being relatively smaller, the radios of 

 injury calculated on that number will be too large; while with the picked apples the case 

 will be reversed. 



The ratios were consequently corrected throughout by the use of the following formulte: 



FALLEN FKUIT. 



c 



Formula — (1) x =- (a-\-x) h — c ( 2 ) ?/ = 



h— , 

 a-y X 



a = Fallen fruit, experimental tree. 



6 = Fallen fruit, ratio of injury, check tree. 



c = Fallen fruit, total injured, experimental tree. 



X = NumVier of apples saved from falling. 



y = Ratio of saved apples to total losable. 



— = Corrected ratio of injury, fallen fruit, experimental tree. 



a 



PICKED FRUIT. 



/ 



e. 



Formula —( 3 ) s = ('c? — x) e — /(4)^=- 



[The above (three and four) are the correct formulaj. Those actually used substituted s for 

 * in both cases. Not having picked all the apples on the trees, I could not subtract x from d.J 

 d = Apples picked, experimental tree, 

 e = Ratio of injury, check tree. 

 / = Total injured, experimental tree, 

 s = Number picked apples saved from becoming wormy. 

 t = Ratio saved apples to total loiable. 



