VI PREFACE. 



I have to apologize to Entomologists for having 

 violated an established rule, by changing the name 

 of an insect ; I found, however, that such confusion 

 would attend my adoption of their name, " Rapae," 

 or turnip, for the destroying Aphis, that I at once 

 determined, for the sake of perspicuity, to call it in 

 my work the " Vastator." 



This work has required some labor in its pre- 

 paration ; at times I have frequently had to tra- 

 verse many miles, in order to determine a single fact. 

 For the purpose of ascertaining the existence of the 

 disease in any plant, it was not sufficient merely to 

 examine it in one locality ; it might not have been 

 attacked at that spot ; the insect might have left the 

 plant, or the plant might not grow in the place which 

 I visited. 



This work also required a knowledge of Botany, 

 Entomology, Chemistry, and Agriculture. I cannot 

 be expected to be conversant with all these 

 matters, for each, alone, would take a long 

 lifetime to acquire. I am therefore fully aware 

 of the great imperfection of the work in these 

 particulars ; but I trust that the development of the 

 Cause of the disease in the potatoe, and the disco- 

 very that it attacks other plants, will prove useful to 

 mankind. 



As soon as I perceived that it would be necessary 

 to write a small Treatise on the subject, I pressed 

 numerous friends into my service, and I obtained 

 valuable assistance in numerous quarters. To all 



