kept in jars for ornament: some seeds will sprout and grow luxuriantly, if they are spread on a woollen cloth and kept moist: branches of the houseleek will give out fresh leaves and shoots, if suspended only in a damp and moist atmosphere. Many most decisive experiments might be adduced to prove that the soil does not afford the nutriment; it is chiefly beneficial in fixing the root steadily in the ground: but as water and air are always present, and absolutely requisite to the growth of vegetables, and as these must be present, one or other, or both of them, must be the source from whence they derive their aliment. That water acts an important part in the process of vegetation, and is largely taken up by the roots of the plant, is known, as well by the earth in which a plant grows becoming soon dry after it has been watered, and also by the vigorous growth of a plant when well watered, which was before drooping for want of it; and likewise by the growth of many species of plants in water alone. In considering the part which atmospheric air acts in vegetation, we must remember that it is a compound of two sorts of gas, one of which, viz. azotic gas, and likewise carbonic acid gas (found in small quantities in the atmosphere, and also in water and in the soil), are, probably, very efficient agents in the growth and nourishment of plants. Water, moreover, is a compound of two kinds of gas, viz. oxygen and hydrogen and carbonic acid gas is a compound of oxygen and carbon. Water and air, then, which are supposed to be the chief food of plants, consist of oxygen, azote, hydrogen, and carbon. Now, all the various parts and productions of vegetables are resolvable into water, hydrogen gas and charcoal, and, of course, into oxygen, hydrogen and carbon, which are, probably, the food of plants, and the bases of their various productions. Water taken up by the absorbent vessels is decomposed in the course of circulation: the oxygen is evolved in the form of pure air, while the hydrogen is fixed as a component part of oils, resins, gums, &c. Carbonic acid gas, taken in by the roots, and partly absorbed from the air, is likewise decomposed ; its pure air is evolved, and its carbon fixed in the formation of wood and other parts. In a similar manner the azote is absorbed from the atmosphere, and also from decayed animal and vegetable matter. Certain earths seem also essentially requisite in some cases thus some plants afford much lime or calcareous earth; others, as reeds, rushes, grasses, and the stalks of all that are hard and glazed like them, contain siliceous or flinty earth, which, perhaps, in some way or other, is absorbed from the soil in which they exist. Upon the whole, then, it may be inferred that the soil itself, and a certain state of it, is requisite to the healthy growth of most plants, although it afford but little if any nutriment. That is the best soil, which, besides affording a sufficiently firm support, and being loose enough to suffer the roots to extend, absorbs and retains moisture long enough to prevent drought, but still suffers it to percolate, and drain off so fast, as to prevent its excess. As different plants have roots of different kinds, and different lengths, and as some require much more moisture than others, the same soil cannot equally suit all plants; some require a light, some a stiff, some an arid, some a swampy soil. Light is required for healthy vegetation. Plants, deprived of it, become pale and sickly: it is only during the action of the sun's rays upon plants that they exhale pure air: hence light is probably essential in the decomposition of water, which is one of the indispensible requisites in the growth of vege-* tables. The bleaching effects of excluding the light, proves that the deposition of the green colouring matter of plants depends upon some process which is the immediate consequence of the action of light, and only takes place where the light gains access. Celery is blanched by earthing it up, and thus excluding the light. Lettuces, cabbages, &c., are rendered white within by tying up the outer leaves, so as to exclude the light and plants, that grow in places from which the light is nearly excluded, are pale, languid, and sickly. : 2 The effects of heat in promoting vegetation are every where apparent. apparent. In the winter season vegeta-` tion is almost at a stand, and it is not till the reviving warmth of spring approaches, that the sap rises, and the plants grow. The forcing of early fruits, flowers, &c., and the production of plants natural to warmer climes, depend wholly on the due application of an increased temperature. Heat applied to a part only of a tree promotes the vegetation of that part only: if, for instance, a branch of a vine be trained into a hothouse, that branch puts out its leaves earlier and affords fruit sooner than the rest. The different processes of vegetation, like the circulation and respiration of animals, tend to maintain a certain uniform temperature; and, as the heat of the animal body is the same at the tropics and at the poles, so the temperature of a healthy tree is higher than that of the air in winter, but colder in the height of summer. Nothing is more worthy of attention than the order and succession of flowering plants, and their infinite variety; but as we have already spoken at length on this subject', we shall conclude our Introduction with some excellent reflections by Dr. (now Sir J. E.) Smith 2. The student in botany has a rich source of innocent pleasure. He would find himself neither solitary nor desolate, had he no other companion than a "mountain. daisy," that "modest crimson-tipped flower," so sweetly sung by one of nature's own poets. The humblest weed or moss will ever afford him something to examine or illustrate, and a great deal to admire. Introduce him to the magnificence of a tropical forest, the enamelled meadows of the Alps, or the wonders of New Holland, and his thoughts will not dwell much upon riches or literary honours. Whether (adds the same author) we scrutinise the damp recesses of woods in the wintry months, when the numerous tribe of mosses are displaying their minute but highly interesting structure ;-whether we walk forth in the early spring, See T. T. for 1814, pp. 133-137. See also the present volume, pp. 154-158, and poetical descriptions of flowers, at pp. 128, 178, 203. 2 Introduction to Physiological and Systematical Botany [Pref. pp. xix, xxi], the best elementary work extant on this subject. when the ruby tips of the hawthorn bush give the first sign of its approaching vegetation, or a little after, when the violet welcomes us with its scent, and the primrose with its beauty;-we shall always find something to study and admire in their characters. The yellow blossoms of the morning that fold up their delicate leaves as the day advances, others that court. and sustain the full blaze of noon-and the pale nightscented tribe which expand and diffuse their sweet fragrance towards evening,—all have peculiar charms. The more we study the works of the Creator, the more wisdom, beauty, and harmony, become manifest, even to our limited apprehensions; and while we admire, it is impossible not to adore.' For the amusement, or, at least, the instruction, of the fair sex, we add the following lines from the Contemplative Philosopher : Ye lovely Fair, while flowery chaplets bind Your youthful brows, and o'er the verdant paths Vain is their blaze, which, like the noontide day, So beauty fades, so fleets its showy life, |