PREFACE ix 



only are the articles explicitly related to each other. 

 It has seemed well therefore to allow the order of 

 chapters to stand as in the English edition. 



Grateful acknowledgment is here made for val- 

 uable help given by Mr. Hubert M. Canning and Mr. 

 Wilbur F. Dubois; also by Dr. Alfred Render of 

 the Arnold Arboretum to whom I owe the note on 

 Cytisus. 



LOUISA YEOMAN s KING. 



