viii PREFACE. 



to them an immense number of his own. Many 

 other naturalists for instance, Axell, Bennett, Del- 

 pino, Hildebrand, Hooker, F. Miiller, and Ogle, have 

 also published valuable memoirs on the subject, to 

 which I shall frequently have occasion to refer ; but 

 to the works of Sprengel, Darwin, and Dr. H. Miiller 

 I am indebted in almost every page, and in spite 

 of constant references, it is impossible for me ade- 

 quately to acknowledge my obligations to them. 

 In the systematic portion, I have followed Mr. Ben- 

 tham's excellent " Handbook of the British Flora." 



As far as possible, I have avoided the use of 

 technical terms, but some were unavoidable; refer- 

 ences for these will be found in the Index, and I have 

 aiso given a Glossary of the technical terms most fre- 

 quently employed. 



I have to thank various friends who have been 

 good enough to assist me, but especially Dr. (now Sir 

 Joseph) Hooker and Mr. Busk, who have been so very 

 kind as to look through my proofs. 



In conclusion, I must add that the subject is com- 

 paratively new, and many of the observations Jiave 

 not yet stood that ordeal of repetition which they 

 will no doubt experience. While, therefore, I believe 

 that the facts will be found to be in the main correct, 

 the inferences drawn from them must, in many cases, 

 be regarded rather as suggestions than as well esta- 

 blished theories. The whole subject is one which 

 is most interesting in itself, and will richly repay 

 those who devote themselves to it. 



HIGH ELMS, DOWN, KENT, 

 September, 1874. 



