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PREFACE 



I wish to express my appreciation to 

 Doctor G. Steiner, Doctor J. R. Christie and 

 Miss E. M. Buhrer, of the Division of 

 Nematology, U. S. Bureau of Plant Indus- 

 try, for their helpful suggestions concerning 

 certain subjects and criticisms of the 

 chapter's I have written wholly or in part. 

 To Dr. H. J. Van Cleave of the Department 

 of Zoology, University of Illinois, gratitude 

 is due for his criticisms of the chapter on 

 "Nemic Relationships"; as was to be ex- 

 pected he did not wholly agree with the 

 treatment of this controversial subject. Mr. 

 Jonas Bassen of the U. S. Bureau of En- 

 tomology and Plant Quarantine has aided 

 through the translation of Russian articles 

 and Miss Dorothy Bero has checked the 

 bibliographies. 



Mr. G. A. Grille of the Spencer Lens 

 Company, Washington, D. C, kindly sup- 

 plied the photograph of Dr. Hall. 



Section I, Part III includes a chapter 

 by Doctor Reed 0. Christenson with con- 

 tributions by Dr. F. G. Wallace, Mr. Leon 

 Jacobs and Mi-s. M. B. Chitwood. Section 

 II, Part I contains chapters by Dr. A. C. 

 Walton and Mrs. M. B, Chitwood; they as- 

 sume full responsibility for the contents of 

 their chapters unless otheiwise noted. I 

 wish to express my appreciation for the 

 fine way I feel they have handled their 

 subjects. I assume responsibility for the 

 nomenclature used. 



B. G. C. 



