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III. — Elementary Introduction to the subject of Verjetable Physio- 

 logy. By Arthur Henfrey, F.R.S., F.L.S., Professor of 

 Botany, King's College, London, &c. 



The object of the present paper is to present a brief sketch of 

 some of the more important bearings of physiological science upon 

 agriculture, through the medium of certain facts, ascertained within 

 recent years by vegetable physiologists, throwing important light 

 upon the phenomena which occur in the growth and nutrition of 

 plants. These are the more opportunely bi'ought forward now, 

 since they illustrate that most important question, recently in 

 full debate, the influence of nitrogenous substances when applied 

 to hasten and increase the growth of plants. We shall endea- 

 vour to explain in language comprehensible without previous 

 acquaintance with technical terms (the " short-hand " of science), 

 the essential points in the development of vegetable structure, 

 without a knowledge of which we can have no secure basis for 

 the establishment of the laws of vegetable physiology. Scien- 

 tific readers may perhaps find some of the explanations too 

 rudimentary, but it may be observed that the most important 

 facts, those connected with the mutual relations of the cellulose 

 and the nitrogenous structures, will be new to all those who have 

 not made it their business to study the additions to knowledge 

 made in the department of physiological botany during the last 

 few years. 



We shall commence by a short discussion of the relations of 

 chemistry to physiological inquiries of the present kind, passing 

 on to the peculiar conditions of the phenomena to be observed 

 in plants ; and then, as necessarily involved with those, we shall 

 briefly state the methods we employ, and the nature and value 

 of the instruments with which we pursue them. We claim the 

 patient attention of the reader to this exordium, in order that he . 

 may be enabled to estimate adequately the importance of the 

 minute, and, as some might imagine, trifling particulars of 

 vegetable life, into which we shall subsequently enter. 



A distinguished chemical writer * has expressed an opinion 

 that " it is chiefly to chemistry that we must look for the exten- 

 sion and improvement of physiological science." With the very 

 highest appreciation of the importance of chemistry, as one of the 

 indispensable foundations upon which physiology must rest, or, 

 if we may so express it, one of the quarries from whence it must 

 derive the materials for its construction, we cannot admit that 



* Gregory, ' Outlines of Chemistry,' p. 564. 



