1838] 



FA K M \: n s' R i<:(,\ st i: r 



67^ 



orirans; and it is by exaniininfr their physica! niid 

 chemical conslitiilion, and the subslanccs iiiui 

 powers which act upon ihem, and tho niudilicu- 

 tions which tiiey uiulcriro, tiiat tho scientific prin- 

 ciples of aijjricuitural chemistry arcohtained. 



According to these ideas, it is evident ti)at the 

 ptudy ouirht to be commenced by some general 

 incpiiries into the composition and nature of ma- 

 terial bodies, and the laws of their changes. The 

 surface of tiic earth, the atmosphere, and the wa- 

 ter deposited from it, must cither together or se- 

 parately ad'ord all the principles concerned in ve- 

 getation; and it is only by examining the chemi- 

 cal nature of these principles, that we are capable 

 of discovering what is the food of plants, and the 

 manner in which this food is supplied and pre- 

 pared lor their nourishment. The principles of 

 the constitution of bodies, consequently, will Ibrm 

 the first subject lor our consideration. 



JJy methods of analysis dependent upon che- 

 mical and electrical instruments dicovered in late 

 times, it has been ascertained that all the varie- 

 ties of material substances may be resolved into a 

 comparatively small number of bodies, which, as 

 they are not capable of being decompounded, are 

 considered in the present state of chemical know- 

 ledge, as elements. The bodies incapable of de- 

 composition at present known are fifiy-two.* Of 

 these, ibrty are metals; eight are inflammable 

 bodies; and five are substances which unite with 

 meials and intlamm-^.ble bodies, and form with 

 them acids, alkalies, earths, or other analogous 

 compounds. The chemical elements acted upon 

 by attractive powers combine in different aggre- 

 gates. In their simpler combinations, they pro- 

 duce various crystalline substances, distinguished 

 by the regularity of their (orms. In more com- 

 plicated arrangements, they constitute the varie- 

 ties ol' vegetable and animal substances, bear the 

 higher character of organization, and are render- 

 ed subservient to the purposes of lilt;. And by 

 the influence of heat, light, and electrical powers, 

 there is a constant series of changes; matter as- 

 sumes new forms, the destruction of one order of 

 beings tends to the conservation of another; solu- 

 tion and consolidation, decay and renovation, are 

 connected; and whilst the parts of the system 

 continue in a state of lluctiiation and chantre, the 

 order and harmony ol' the whole remain unaltera- 

 ble. 



Alter a geiier;d view has been taken of the na- 

 ture of tiie elements, and of the principles of che- 

 mical changes, the next object will bi; the struc- 

 ture and constitution ol" plants. In all plants there 

 exists a system of tubes or vessels, which in one 

 extremity terminate in roots, and at the other in 

 leaves. It is by the capillary aciion of the n^ois 

 that fluid matter is taken up from thcs(*il. The 

 sap, in [lassing upwards, becomes denser, and 

 more fitted to depusiie solid matter: it is iiiodiliei' 

 by exposure to heat, light, and air in the leaves; 

 descends tiiroiigh the bark, in its progress produ- 

 ces new organized matter; and is thus, in its ver- 

 nal and autumnal flow, the cause of the forma- 

 tion of new parts, and of tlie more perltjct evolution 

 of parts already lljrmed. 



* The number is now^ fil'ty-fbur. Since tho above 

 was written, thorium has been discovered by Beize- 

 lius, and vanadium by Sefstrom; both of them metals, 

 as their tcimiiiatioii indicates. — J. D. 



In this part of tlie inquiry, I shall endeavor to 

 connect together into a general view, the observa- 

 tions of the most enlightened philoso[)hers who 

 have studied the j)hyHiology ol' vegetation. 

 Those of (rrew, JMal|)higlii, Sennebier, J)arwin, 

 l)e ("andolle, JMirbel, and, above all, of JVlr. 

 Knight, lie is the latest iiKjuirer into these in- 

 teresting subjects, and his labors have tended 

 most to illustrate this part of the economy of na- 

 ture. 



The chemical composition of plants has, within 

 the last ten years, been elucidated by the experi- 

 ments of a number of chemical philosopers, both 

 in this and in other countries; and it forms a beauti- 

 ful part of general chemistry. It is too extensive 

 to be treated of minutely; but it will be necessary 

 to dwell upon such parts of it, as afford practical 

 inferences. 



If the organs of plants be submitted to chemi- 

 cal analysis, it is found that their almost infinite 

 diversity of lorrn depends upon different arrange- 

 ments and combinations of a very few of the ele- 

 ments; seldom more than seven or eight belon<T to 

 them, and three constitute the greatest part of 

 their organized matter; and accordiiig to the man- 

 ner in which these elements are disposed, arise 

 the different properties of the products of vegeta- 

 tion, whether employed as food, or lor other pur- 

 poses and wants of life. 



The value and uses of every species of agricul- 

 tural produce, are most correctly estimated and ap- 

 plied, when practical knowledge is assisted by 

 principles derived fi-om chemistry. The com- 

 pounds in vegetables really nutritive as the food 

 of animals, are very lew; farina or the pure mat- 

 ter of starch, glu1en,sugar, vegetable jellv, oil, 

 and extract.* Of these the most nutritive is glu- 

 ten; which apjjfoaches nearest in its nature to ani- 

 mal matter, and which is the substance that irives 

 to wheat its eu|)eriority over other grain. "The 

 next in order as to nourishing power is oil, then 

 sugar, then farina; and last of all, gelatinous and 

 extractive matters. Simple tests of the relative 

 nourishing powers of the difi'erent species of food, 

 are the relative quantities of these substances that 

 they aflbni by analysis; and though taste and ap- 

 pearance must influence the consumption of all 

 articles in years of plenty, yettheynre less attend- 

 ed to in times of scarcity, and on such occasions 

 this kind of knowledge may be of the greatest im- 

 portance. Sugar and iiirina, or starch, are very 

 similar in (;om|)osition, and are capable of being 

 converted into each other, by simple chemical pro- 

 cesses. In the discussion of their relations, I shall 

 detail to you the results of some recent experi- 

 ments, which wdl be fijund possessed of applica- 

 tions both to the economy of vegeiaiion, and to 

 some imporlaiM. processes of inanuliicture. 



All tlie v;tiif!ies of substances found in plants, 

 are produced liom tfie sap; and the sap of plants is 

 derived lioin water, or from thefiuidsofthesoil, and 



* Doubt may be entertaini'd of the number being- so 

 limited. As the saw-dust of wood is capable of being 

 converted into a kind of bread, by a peculiar process, 

 it i« not improbable that, by the digestive powers of 

 animals, nourishment may be derived from substantes 

 analogous to saw-dust, as chaff, 8cc. In the Ionian 

 islands, where cattle are miserably kept during the 

 winter months, they are fed chiefly on straw, and the 

 horses of the farmer on straw and the cuttings of the 

 vine, — J. D. 



