PREFACE. 



IN the autumn of 1833, during a period of convalescence from a severe attack of the fever of 

 the Southern States, my thoughts were first turned to the connexion of Chemistry with Vegetable 

 Physiology. 



At that time, as the works on Chemistry show, comparatively but little advance had been made 

 in this interesting department of science. In the most popular treatises, Organic Chemistry consisted 

 chiefly of a descriptive history of the acids and bases of the vegetable and animal kingdoms. 



It is impossible for any one to witness in those warm climates the rapidity with which all the 

 operations of vegetable life are carried on, without having his thoughts directed to the obvious con- 

 nexion which exists between these phenomena and external agents. Even in the opinion of the 

 uneducated planter, the rapidity of vegetable growth is connected with the warmth of the season, 

 and the occurrence of favourable rains, and the brilliancy of the sun. 



A seed which has been buried in the ground a few days, makes its appearance above the surface. 

 It soon puts forth its leaves, which turn green in the light, and becomes an active laboratory of all 

 kinds of chemical and mechanical processes. Starch, gum, sugar, and a variety of other substances 

 are formed from inorganic matter, water is drawn up in large quantities from the ground, and 

 evaporated from the leaves. 



All these phenomena unquestionably depend on the common laws of physics. Our interest in 

 them is greatly increased by the close resemblance of many of them to things taking place in the 

 case of animal systems. The productions of vegetable life are, many of them, also apparently the 

 productions of animal life. The physical processes which appear in one of the great classes of 

 living beings, appear in the other too. Inquiries into the nature of the vital processes of plants end 

 in resolving problems connected with the physiology of animals. 



In every plant there are two prominent operations carried forward : the production of organic 

 matter, and its distribution through the various parts of the vegetable system. It is to the consid- 

 eration of these that the following pages are chiefly devoted. As to the various transformations 

 which take place in the interior of these organisms, and the chemical principles involved in those 

 changes, anything which I might offer would be insignificant, compared with the splendid results 

 which have been obtained by the German, French, and English chemists during the period which 

 has elapsed since these researches were first undertaken. 



Any one who peruses the works on Botany and Vegetable Physiology must be struck with the 

 inexact views which are entertained on the mode of action of the solar rays in producing the green 

 colour of plants, and effecting the decomposition of carbonic acid gas. Yet this is unquestionably 

 the most remarkable result in physiological and physical science. It is the transmutation of inor- 

 ganic into organized matter. With a view of giving clearness and precision to those vague notions, 

 I have devoted much of the following work to this point, showing how, as plants grow in water or 

 in air, they are furnished, upon physical principles, with nutrient material ; how, upon this, the sun- 



