AGKICULTUKAL CHEMISTRY. 



95 



organized matter. Azote, phosphorus, 

 sulphur, manganesum, iron, silicum, cal- 

 cium, aluminum, and mngnesium, like- 

 wise, in different arrangements, enter into 

 their composition, or are found in the 

 agents to which they are exposed; and 

 these twelve undecompodnded substances 

 are the elements, the study of which is of 

 the most importance to the agricultural 

 chemist. 



The doctrine of definite combinations, 

 as will be shown in the following lectures, 

 will assist us in gaining just views respect- 

 ing the composition of plants and the eco- 

 nomy of the vegetable kingdom; but the 

 same accuracy of weight and measure, the 

 same statical results which depends upon 

 the uniformity of the laws that govern 

 dead matter, cannot be expected in opera- 

 tions where the powers of life are concern- 

 ed, and where a diversity of organs and of 

 functions exist. 



The classes of definite inorganic bodies, 

 even if we include all the crystalline ar- 

 rangements of the mineral kingdom, are 

 few, compared with the forms and sub- 

 stances belonging to animated nature. 

 Life gives a peculiar character to all its 

 productions; the power of attraction and 

 repulsion, combination and decomposition, 

 are subservient to it; a few elements, by 

 the diversity of their arrangement, are 

 made to form the most different substan- 

 ces, and similar substances are produced 

 from compounds which, when superficial- 

 ly examined, appear entirely diiferent. 



LECTURE IIL 



On the Organization of Plants. Of the 

 roots, trunk, and branches. Of their 

 structure. Of the Epidermis. Of the 

 cortical and alburnous parts of leaves, 

 Jiowers, and seeds. Of the chemical 

 constitution of the organs of plants, 

 and the substances found in them. Of 

 mucilaginous, saccharine, extractive, 

 resinous and oily substances, and 

 other vegetable compounds, their ar- 

 rangements in the organs of plaiits, 

 their composition, changes and uses. 



Variety characterizes the vegetable 

 kingdom, yet there is an analogy between 

 the forms and the functions of all the dif- 

 ferent classes of plants, and on this analo- 



gy the scientific principles relating to their 

 organization depend. 



Vegetal)les are living structures distin- 

 guished from animals by exhibiting no 

 signs of perception or of voluntary mo- 

 tion; and their organs are either organs of 

 nourishment or of reproduction, organs 

 for the preservation and increase of the in- 

 dividual, or for the multiplication of the 

 species. 



In the living vegetable system there are 

 to be considered, the exterior form, and 

 the interior constitution. 



Every plant examined as to external 

 structure displays at least four systems of 

 organs, or some analogous parts. 

 Fiist, the Root. 



Secondly, the Trunk and Branches, 

 or Stem. 



Thirdly, the Leaves. 

 And fourthly, the Flowers or Seeds. 

 The root is that part of the vegetable 

 which least impresses the eye; but it is 

 absolutely necessary. It attaches the plant 

 to the surface, is its organ of nourishment, 

 and the apparatus by which it imbibes food 

 from the soil. 



The roots of plants, in their anatomical 

 division, are very similar to the trunk and 

 branches. The root may indeed be said 

 to be a continuation of the trunk, termina- 

 ting in minute ramifications and filaments, 

 and not in leaves; and by burying the 

 branches of certain trees in the soil, and 

 elevating the roots in the atmosphere, 

 there is, as it were, an inversion of the 

 functions — the roots produce buds and 

 leaves, and the branches shoot out into 

 radical fibres and tubes. This experiment 

 was made by Woodward on the willow, 

 and has been repeated by a number of 

 physiologists. 



When the branch or root of a tree is cut 

 transversely, it usually exhibits three bo- 

 dies — the bark, the wood, and the pith; 

 and these again are individually suscepti- 

 ble of a new division. 



The bark when perfectly formed is co- 

 vered by a thin cuticle or epidermis, 

 which may be easily separated. It is ge- 

 nerally composed of a number of laminae 

 or scales, which in old trees are usually in 

 a loose and decaying slate. The epider- 

 mis is not vascular, and it merely defends 

 the interior parts from injury. In forest 



