1362. The functions of the trunk are those of the tissues, systems and members; thus first of the cells, vessels or ducts and tracheæ; secondly, of the bark, liber and wood; lastly, of the root, stalk and foliage.
1. Facts.
1363. The phenomena to be regarded in plants bear relation to their constituent parts, and the changes or preliminary incidents which they undergo.
A. Constituent Parts.
The chemical constituent parts of vegetables are inorganic and organic.
a. INORGANIC BODIES.
Elements.
1364. The plant contains all the primitive bodies; carbon, oxygen, hydrogen and nitrogen. The carbon forms the principal mass, and almost alone constitutes its solid parts. The nitrogen is only present in small quantity, being, as it were, a trace only of the future animal kingdom.
1365. In the plant all the elements are also active, as the æther, which, through the gravitation of the root, strives towards the middle point or centre of the earth. The light, which imparts the general polarity and decomposition, as well as produces colours. The latter appear to reside in the starch-flour. The heat, that sustains the indifference, promotes the evaporation and the course of the sap, as also protects the plant from being killed by frost or cold. The air that penetrates through the spiral vessels to all parts, and is also met with occasionally in the hollow stalks, the interstices and cells of the pith and cuticle. It imparts the process of oxydation. The water is the proper mother of the plant, being the medium by which the nutrition is imparted. It contains in a state of absorption some hydrogen and nitrogen, a larger amount of oxygen, and abundance of carbonic acid; besides different salts, mucus, sugar, and acids. The earth, as element, bestows upon the plant a firm station, so that the water-and air-organs continue separate from each other.
Minerals or Earths.