VI PREFACE. 



and to the application of the knowledge thus acquired to 

 the improvement of the art of cultivation, whether in the 

 field, the garden, or the hothouse. 



The first part of the following volume is, therefore, 

 devoted to an exposition of this part of Botanical science ; 

 and the Author has endeavoured to state in the Introduc- 

 tion some of the inducements which may incite to the 

 study of it. He may here remark, in addition, that the 

 progress of science is continually rendering closer and 

 closer that relation between the physiology of plants 

 and that of animals, which it was the Author's intention 

 to develope, in his " Principles of General and Compara- 

 tive Physiology," first published in 1838. It had long 

 been admitted, that the physiology of man cannot be 

 properly understood, unless studied in connection with 

 that of the lower animals; and the truth, that the 

 physiology of animals cannot be properly understood, 

 unless it be studied in connection with that of plants, is 

 now becoming generally recognized. Those who shall 

 peruse the Treatise on Animal Physiology in this series, 

 after they have made themselves acquainted with the first 

 part of the following volume, will not find it difficult to 

 perceive the connection here referred to. 



With regard to the portion of the volume devoted to 



