term including all plants and roots which grow above and under ground; being nourished by the air, water, &c.—See Food of Plants.
The different classifications of plants by Ray, Tournefort, Linnæus, and other eminent botanists, having already been mentioned, vol. i. pp. 316-17; we shall at present confine our attention to the constituent parts of vegetables, and conclude with a few directions for collecting and preserving simples, both for medicinal and economical purposes.
According to the most accurate chemical analysis, plants have been found to contain:
1. Sugar; to which we refer.
2. Starch; which see.
3. Gluten is a viscid matter, that remains after washing wheaten flour, in the preparation of starch, and which also subsides when paste is repeatedly washed with cold water, till that fluid become perfectly transparent. It is very tenacious; and, if combined with the nitric, it may be converted into the oxalic acid, which is known under the name of Essential Salt of Lemons.
4. Albumen; 5. Jelly; 6. Gum; 7. Camphor; and, 8. Resin; to which we refer.
9. Caoutchouc, or Elastic Resin, is obtained not only from the tree mentioned in that article, but exists in numerous plants, particularly the misletoe, from which it may be extracted by infusion in water.
10. Wax; 11. Acids; 12. Alkalies (see also Barilla, Kelp, Pot-ash, &c.); 13. Oil; all of which have already been explained.
13. Earths:—for instance, lime, which abounds in almost every plant; silica, or pure flint, has been discovered in the different species of Horsetail and Grass; magnesia, which occurs chiefly in the marine plants, particularly the Sea-wrack, and the exotic species of the Saltwort, or Salsola soda; and lastly, alumina, or pure clay, which is found only in a few vegetables.
15. Several metallic sulstances have likewise been chemically separated; though in very small portions. Thus M. Sage has clearly proved that gold exists in many plants; M. M. Scheele and Prouse have obtained manganese from the ashes of the Vine, Green Oak, Fig-tree, Pine, &c. Iron also forms an ingredient in almost every plant, but particularly in the different species of the Saltwort.
16. The Woody Fibre is the basis of all vegetables: it abounds mostly in trees, but occurs less frequently in herbs; is insoluble either in water or alkohol, but is acted upon by alkalies; and is also decomposed by the mineral acids: when burnt in a smothering heat, it yields a large proportion of Carbon, or Charcoal.
The mode of collecting vegetables, or simples, varies according to their peculiar nature, and the different parts to be preserved. Thus, annual roots should be dug up before they shoot forth either stalks or flowers; biennials in the autumn of the year in which they were sown; and perennials also in the autumn: though some naturalists prefer the spring for the collection of the latter; because at that season they abound with juice, or sap: but, as they are then apt to shrivel in drying, the autumn is doubtless the most proper time for such purpose.
