Xll PREFACE TO THE 



the weak-drawn state of forced Asparagus in London is occa- 

 sioned by the action of the dung immediately upon its roots!" 



It does not seem possible to account for this in any other way 

 than by referring it to the want of some short guide to the 

 horticultural application of vegetable physiology, unmixed with 

 other things ; and so arranged that the intimate connexion of one 

 branch of practice with another, and of the whole with a few 

 well ascertained facts upon which everything else depends, may 

 be distinctly perceived from a single point of view. The 

 admirable papers of Mr. Knight are scattered through the 

 Horticultural Transactions ; and the writings of other physiolo- 

 gists are dispersed through so many different works, that the 

 labor of finding them, when wanted, is greater than is willingly 

 undertaken even by those who have access to ample libraries. 

 With regard to general works on Horticulture, it is very far 

 from my wish to say one word in disparagement of the many 

 excellent publications upon this subject which have already 

 appeared in this country; on the contrary, the improved state 

 of gardening among us may be reasonably ascribed to the 

 influence of some of these valuable works : but it must be 

 admitted that the true principles of physiology are not, in sueb 

 books, so separated from the details of routine on the one hand, or 

 so applied to them on the other, as to be readily understood by 

 those who want either the skill or the inclination to distinguish 

 empirical directions from rules which are plainly founded upon 

 the very nature of things. I must also be permitted to observe 

 that, although results are correctly stated in such books, they 

 are not unfrequently referred to wrong causes. 



In preparing the following pages for the press, my anxious 

 desire has been to strike out all unnecessary matter, even 

 although it may be required to complete the physiological 



