PREFACE IX 



printed books and bulletins, it has been rewritten and recombined, so as 

 to become a part of the warp and woof of the finished literary fabric 

 herewith presented. 



It is hoped, that this handbook will appeal to the student of plant 

 life, particularly to the people, who, as agriculturalists, stock raisers and 

 veterinarians, want to know something concerning the botany of the 

 economic plants of interest to them in their agricultural, pastoral, or 

 professional work. The plants chosen for treatment in the descriptive 

 text, as the injurious, or useful, are those which have proven to be so. 

 Plants of doubtful position in these respects have been omitted. The 

 writer wishes to acknowledge the help of Dr. John A. Kolmer of the 

 Medical School, of the University of Pennsylvania, who has read the pages 

 on the phytotoxins and Ehrlich's theory of immunity; of Dr. C. Dwight 

 Marsh, Expert, Poisonous Plant Investigations, Bureau of Plant Indus- 

 try, U. S. Department of Agriculture for cooperation in securing the use 

 of published departmental photographs and to Mr. C. V. Brownlow of 

 the firm of P. Blakiston's Son & Co. for the encouragement, which he 

 has given during the publication of the book. 



JOHN W. HARSHBERGER. 

 Philadelphia, July 31, 1920. 



