BOOK II. 



OF THE PHYSIOLOGICAL PRINCIPLES UPON "WHICH 

 THE OPERATIONS OF HORTICULTURE ESSENTIALLY 

 DEPEND. 



Every operation in horticulture depends for suc- 

 cess upon a correct appreciation of the nature of the 

 vital actions described in the last Book ; for although 

 there have been many good gardeners entirely unac- 

 quainted with the science of vegetable physiology, and 

 although: many points of practice have been arrived at 

 altogether accidentally yet it must be obvious that the 

 power of regulating and modifying knowledge so ob- 

 tained cannot possibly be possessed, unless the external 

 influences by which plants are affected are clearly un- 

 derstood. Indeed, the enormous difference that exists 

 between the skill of the present race of gardeners and 

 their predecessors can only be ascribed to the general 

 diffusion, that has taken place, of an acquaintance with 

 some of the simpler facts in vegetable physiology. 



In attempting to apply the explanations of science 

 to the routine of horticultural practice, it appears de- 

 sirable, in order to avoid frequent repetition, that all 

 the subordinate details of the art should be omitted, 

 and that those general operations should alone be ad- 

 verted to which, under many different modifications, 

 and in various forms, constitute the foundation of 

 every gardener's education. 



