Chemical composition of the Sap. The sap is a transparent, colourless fluid, imbibed by the vegetable from the earth and air; or more properly, from the water existing in them, which holds in solution oxygen, hydrogen, carbon, nitrogen, earths, mineral-salts, and animal and vegetable matter. We might suppose, that being derived from the same source, the sap in all vegetables would be alike, but it is never obtained pure; it is mingled with the proximate principles, or proper juices, and thus differs in different species of vegetables; water, however, constitutes the principal part in all. The following result of the analysis of the sap of some vegetables has been offered by a French chemist.* Sap of the,elm, (ULMUS campestris,) water, volatile matter, acetate of potash, carbonate of lime, vegetable matter, sulphate of potash. Sap of the beech, (FAGUS sylvatica,) water, acetate of lime, with excess of acid, acetate of potash, gallic acid, tannin, mucous extract, acetate of alumine. Sap of the Horse Chesnut, (ESCULUS hippocastanum,) water, extractive mucous matter, nitre, acetate of potash, and carbonate of lime. These few examples of the decomposition of vegetable principles show how wide a field is open to the chemist, in the study of vegetable elements. It may seem wonderful, that of so few elementary substan ́ces, such a great variety should exist in the taste, smell, colour, consistence, medicinal and nutricious qualities of vegetable -combinations; is it not equally wonderful that, with the nine digits and the cipher, we may make such varied combinations of numbers; or with our twenty-six letters of the alphabet, form every variety of composition? Thus, by the various combinations of a few simple principles, are formed all vegetable and animal productions; and, although formerly, the presence of nitrogen was considered as a test of animal substance, and the want of it of a vegetable substance, it is now ascertained that animal substances may exist without nitrogen, and that this principle is contained in several vegetables. The elements of the compounds being the same, the question naturally arises, what causes the great diversity in the properties? Two causes may be assigned for this; viz. 1st. The * Vauquelin. Sap-Of the elm-Of the beech-Of the horse chesnut-All vegetable and animal productions composed of a few simple principles-Illustration-What two causes assigned for the different properties of compounds formed from the same elements? different proportions in which the elements are combined. 2nd. The various modes of their combination. In In vinegar and sugar, the one substance a liquid, and of a sour taste, the other solid and sweet, are found the same elements in different proportions and differently combined. gum, starch, and sugar, the elements are the same, the tions nearly the same, but they are combined differently. propor. When we know by chemical analysis, the combinations which exist in inorganized bodies, we can by putting the same together, often form similar substances; but we cannot thus form organized bodies; for to these belongs a living principle, which it is not in the power of man to bestow. It is said, Rousseau declared, that he would not believe in the correctness of the analysis of vegetable or animal substances, until he should see a young animal or a thrifty plant spring into existence, from the retort of a chemist. But the power to create, the Almighty has not delegated to man; neither is it to be supposed that any future discoveries in science will ever confer it upon him. To study into the compound nature of substances, to classify, arrange, and by various combinations to beautify the world of matter, to cultivate the faculties of mind, until stronger and brighter, the mental vision sees facts and principles before invisible; these are the high privileges bestowed on man; but to add one new particle to matter, or one new faculty to the mind, is beyond the power of the whole human race. Examples-Can organized bodies be produced by the skill of man? PART III. CLASSIFICATION. Note. As the pupil, in the first part of this volume, is introduced to a knowledge of the leading principles of the Linnæan system, some repetition must necessarily occur in the following part, in which the principles of classification are to be more fully considered. LECTURE XX. Method of Tournefort.-System of Linnæus.-Method of Jussieu: Natural Method of Linnæus. LET us now imagine the whole vegetable kingdom, comprising innumerable millions of individual plants, to be spread out before a botanist. Could he, in the course of the longest life, number each blade of grass, each little moss, each shrub, or even each tree? If he could not even count them, much less could he give each one a separate name and description. But he does not need to name them separately, for he sees that nature has arranged them into sorts or kinds. W ere you sent into the fields to gather flowers of a similar kind, you would need no book to direct you to put into one parcel, all the red clover blossoms, and into another, the white clover; while the dandelions would form another group. These all constitute different species. Nature would also teach you that the red and white clover, although differing from each other in some particulars, yet bear a strong resemblance. By placing them together you form a genus, and to this genus you refer all the different kind's or species of clover. When you see the red, damask, and cinnamon roses, you perceive they all have such strong marks of resemblance as to entitle them to be placed together in one genus. But yet you know that the seed of a damask rose would never produce a red rose. One species of plants can never produce another species, however near may be their resemblance. The whole number of species of plants which have been named and described, including many which have been recently discovered in New Holland and about the Cape of Good Hope, is said to be 56,000.* *According as recently reported by the Baron Humboldt, to the French National Institute. Nature arranges plants into kinds or sorts-Examples-Number of species of plants. If species of plants were described without any regular order, we could derive no pleasure, and very little advantage from the study of practical botany. If we wished to find out the name of a plant, we should be obliged to turn over the leaves of a large volume, without any rule to guide us in our search. The necessity of some kind of system was so apparent, that many attempts for the methodical arrangement of plants, were made, before the time of Linnæus; but his system was so superior to all others, that it was no sooner published to the world, than it was adopted by the universal consent of all men of science. Previous to this time, Tournefort, a native of France, had published an ingenious method of arrangement, beautiful by its simplicity, but imperfect, on account of the vagueness of its application. The characters of his classes were founded upon the absence, presence, and form of the corolla. Tournefort made twenty-two classes; these he subdivided into sections or orders. The first seventeen classes contained herbs and shrubs; the remaining five contained trees. The division of the first seventeen classes, or those which contain herbs and shrubs, was as follows. The first four classes had monopetalous corollas; they were Bell-form, Funnel-form, Labiate and Personate. The seven following classes contained the Cruciform, Rosaceous, Umbelliferous, Caryophyllous, Liliaceous, Papilionaceous, and the Anomalous. The three following included the Compound flowers. The three next following, included; 1st. Plants having Stamens without a corolla. 2d. Such as had no flower. 3d. Such as had neither flower nor fruit. Next followed the arrangement of large and small trees. The eighteenth and nineteenth classes were Apetalous, hav. ing corollas without petals; and Amentaceous, having flowers in a catkin; as the chesnut and willow. The twentieth class contained such large and small trees as had monopetalous corollas. The twenty-first and twenty-second classes contained such large and small trees as had polypetalous corollas; Rosaceous, as the apple and lilac, or papilionaceous, as the locust. Necessity of order in description-Attempts at arrangement made before the time of Linnæus.-Tournefort's classes, on what founded-How many-Mention the divisions of the first seventeen-Eighteenth and nineteenth classesTwentieth class-Twenty-first and twenty-second classes. Flowers Without petals, 12 Flosculus. Composed. 13 Semi-Flosculus. 15 Apetalous with stamens. TREES. Without 18 Trees apetalous. petals. 19 Trees amentaceous. Corollas monopetalous petalous. Corollas polypetalous. 20 Trees with monopetalous flowers. After having derived from the corolla the distinctions of classes, Tournefort subdivided them into orders, or as he called them, sections. These orders were founded upon the observation of the pistil, calyx, fruit, &c. The first step in this classification, or the separation of shrubs and trees was wrong. The distinction between a small tree and shrub, cannot be accurately defined; there are many plants which we should doubt whether to class among large shrubs or small trees. Two circumstances were, by Tournefort, relied on as a foundation for this distinction; viz. that shrubs do not form buds for the future year; and secondly, the difference in the size of trees and shrubs. With respect to the formation of buds, the distinction is not found to be invariable, as some shrubs do form buds, and some trees do not. With respect to size, the variation, even in the same species, is such, in different soils and situations, that it cannot be admitted as a mark of distinction. Synopsis of Tournefort's method-Orders-Defects in Tournefort's classification-Difficulty of determining between buds and shrubs. |