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If a solvent has been the cause, that solvent must have been water, for there is no other fluid in nature in sufficient abundance, to have acted the part of a solvent upon so large a scale.

Hence two distinct theories arise, founded upon these questions: Is the present structure of the solid contents of the earth, so far as it is capable of examination, the result of igneous fusion, or of aqueous solution? Is the Plutonic or the Neptunian system founded on the stronger basis?—The Plutonic theory was first started in modern times by M. Buffon, but its defenders are now chiefly confined to our own country; and consist of Dr. Hutton, Professor Playfair, and Sir James Hall, who are powerfully opposed by the equally respectable authorities of Werner, Saussure, and Kirwan; and it may be added, that the general opinion is much in favour of the Neptunian theory, or that entertained by the last named philosophers. These theories have been discussed in the notes to Mr. Jameson's third volume, to which we have already referred,

In addition to the works noticed as strictly mineralogical, the following is well deserving the student's attention: "An Introduction to Geology, illustrative of the general Structure of the Earth, comprising the Elements of the Science, &c. by Robert Bakewell." According to this author, the knowledge of the structure, composition, and arrangement of the materials, which form mountains, rocks, or strata, constitutes the first part of geology. In the second part is included the direction, structure, and extent of the mineral dykes and metallic veins by which they are intersected. The changes which are taking place on the surface of the globe by the agency of inundations, earthquakes, and volcanoes, make the third part. And the fourth part, or speculative geology, is chiefly confined to an investigation of the causes, that have probably operated in the formation of rocks and mountains, and also those by which the revolutions in the earth's surface have been subsequently affected. Mr. Bakewell's work is illustrated with plates, and he has devoted a long chapter to the Geology of England,

which he concludes by observing, that "there are few extensive estates, whose value would not be greatly increased by a correct knowledge of the mineral substances that they contain. The well known maxim of Lord Bacon, that knowledge is power, is particularly applicable to this subject; for as Sir John Sinclair has justly stated, a knowledge of our subterranean wealth, would be the means of furnishing greater sources of opulence to the country, than the acquisition of the mines of Mexico or Peru."

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CHAP. IX.

NATURAL HISTORY,

Continued.

BOTANY. Parts of a plant described-Root-Body, viz. Trunk-Leaves -Fulchra-Buds. Flowers-Fructification-Calyx-Corolla-Stamina

-Pistilla-Pericarpium-Capsula-Semina-Receptaculum.

Classifi

cation of plants-Systems-Classes, Orders, Genera and SpeciesLinnæus' artificial system-Classes and orders-Jussieu's natural system.

BOTANY is that branch of natural history, which relates to what is called the vegetable kingdom, the second of the three grand assemblages into which all terrestrial objects are divided. As a science, it is not confined to the description and classification of plants, but comprehends many other important particulars, some of which are the following.

I. The description, or nomenclature of the several parts of a plant which are externally visible. Every plant is composed of several parts, which differ from each other in their outward appearance: many of these are themselves compound, and obviously capable of being divided into subordinate parts, The first great division, adopted by most botanists, is into the root, the body of the plant, and the fructification.

The root, according to Linnæus, consists of the radicle and the descending caudex. The radicle is that fibrous part which draws nourishment from the earth, and in many plants constitutes the whole root. The descending caudex is properly part of the stock, or body of the plant, which extends itself below the surface of the ground, as the ascending caudex rises above it.

Roots are divided, according to the term of their duration, into annual, biennial, and perennial. The annual, biennial, and perennial: the two former produce flowers and fruits only once, and then soon die, the annual pass through all the stages of vegetable life in one season: the biennial throw out leaves the first year, but do not complete the fructification till the next. The perennial root has within itself a principle of continued life, and gives being to new flowers and seeds, year after year, for a considerable length of time.

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The body of the plant springs from the root, and is terminated by the fructification: it consists of the trunk, the leaves, the fulchra, props or supports, and the hybernacula or buds.

The trunk bears both leaves and flowers, as the trunks and branches of all trees and shrubs, as well as of many herbaceous plants. By its means the organs of plants are raised to a fit height above the ground, and presented in various directions to the atmosphere and light. In germination, it always takes a contrary direction to the root. As it advances in growth, it is either able to support itself, or it twines round, or adheres to other bodies. The trunk or stem is variously formed in different plants, but our limits do not allow us to enter into particulars.

The leaves are not absolutely necessary to all plants, for on some occasions the stems perform the function of the leaves. They are generally so formed as to present a large surface to the atmosphere; when they are of any other hue than green, they are said to be coloured. Their duration is for the most part annual, but in some trees and shrubs they

survive two or more seasons, and such plants being always in leaf are denominated ever-greens.

Leaves have a natural tendency to present their upper surface to the light, and turn that surface towards it in whatever direction it is presented to them. When trees in leaf are nailed to a wall, and the position of their leaves is consequently disturbed, they soon recover their natural direction. Light evidently acts as a wholesome stimulus to their upper surfaces, and as a hurtful one to the under. When the latter is forcibly presented for a long period to its rays, destruction is the consequence. Leaves seem to require occasional repose from the action of light on their upper surface; for, when it is withdrawn from them, many leaves close or fold themselves together, as if in a state of relaxation, and spread themselves forth again at the returning beams of the morning. This is more especially the case with winged leaves, as those of the pea kind. Those of the white acacia, robinia pseudoacacia, have been remarked by Bonnet, to be over-excited by the sun of a very hot day, and to fold their upper sides together, in a manner directly contrary to their nocturnal posture. The effect of moisture upon leaves, every one must have observed. By absorption from the atmosphere, they are refreshed; and by evaporation, especially when separated from their stalks, they soon fade and wither. Aquatic vegetables, whose leaves are immersed in the water, both absorb and perspire with peculiar facility. Anatomical investigations have shewn that the nutritious juices, imbibed from the earth, and become sap, are carried by appropriate vessels into the substance of the leaves. Knight, in his papers in the Philosophical Transactions, has demonstrated that these juices are returned from each leaf, not into the wood, but into the bark. Hence the theory of vegetation has been established. It appears that the sap is carried into the leaves for the purpose of being acted upon by air and light, with the assistance of heat and moisture. By all these agents a most material change is wrought in its component parts and qualities, differing widely according to the

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