VI PREFACE. 



Robinson has given advice in general treatment and in mat- 

 ters of nomenclature ; Dr. C. W. Swan and Mr. Charles H. 

 Morss have made a critical examination of the manuscript ; 

 Mr. Warren H. Manning has contributed the " Horticultural 

 Values " throughout the work ; and Miss M. S. K. James has 

 prepared the index. To these and to all others who have 

 given assistance in the preparation of this work, the grateful 

 thanks of the authors are due. 



