PREFACE. VH 



of Jena ; in fact for clearness of deiinition they are unsur- 

 passed by any other maker. 



No author could well approach the subject of economic 

 biology without consulting the works of Berkeley, Cooke, 

 Curtis, De Bary, Lindeman, Ormerod, Plowright, Riley, 

 Smith, Taschenberg, Westwood, Whitehead, Woronin, 

 and others : to these,. I take this opportunity of acknow- 

 ledging many obligations. 



My best thanks are given to Dr. Carl Zeiss, Dr. K. 

 Lindeman (Professor in the Academy of Agriculture, 

 Moscow), Messrs. S. T. Griffiths, G. P. Strawson, C, 

 Whitehead, P.L.S., J. E. Mason, L. 0. Howard (Depart- 

 ment of Agriculture, U.S.A.), B. P. Galloway, and the 

 Hon. N. J. Colmau (formerly Commissioner of Agriculture, 

 U.S.A.), for valuable information. 



I may add, that I have received the constant assistance 

 of my wife {n4e Prances E. Wright), whose knowledge of 

 botany has been no mean help to me in many ways. 



In conclusion, I hope that the present volume may 

 prove useful in helping farmers and others to increase 

 the produce of the soil by preventing or curing those 

 diseases caused by the attacks of numberless farm pests. 



A. B. GRIPPITHS. 



