IN making the following selection from the numerous communications ad- 

 dressed by Mr. Knight to the Royal and Horticultural Societies, the object 

 kept in view has been to embody the whole of those which give an account of 

 the important physiological experiments carried on, or facts observed by him, 

 or in which are consigned the theoretical or practical results deduced from these 

 experiments and observations. Those relating to temporary, controversial or 

 other matters, now deprived of the interest they possessed at the time when 

 read, are here omitted. 



In the arrangement of the papers, it has been thought best to adopt the 

 chronological order : thus showing the gradual steps attained by Mr. Knight in 

 the pursuit of his inquiries, and simplifying the references he was in the habit 

 of making to previous memoirs. This order has only been departed from in as 

 far as was necessary to separate the communications made to the Royal Society 

 from those made to the Horticultural Society ; for it has appeared as if Mr. 

 Knight's object, in determining to which body he should address himself, was 

 to place on record, in the Philosophical Transactions, the general physiological 

 principles he laid down, and in the Horticultural Transactions to detail the 

 practical application of those principles. 



Three papers on questions of Animal Economy, of considerable importance, 

 but not immediately connected with Horticulture, or Vegetable Physiology, 

 are given in an Appendix. 



