PROGRESS OF GROWTH IN THE VEGETABLE CREATION. (From Hunt's Poetry of Science.) THE rapid growth of confervo upon water has often been brought forward as evidence of a spontaneous generation, or the conversion of inorganic elements into organic forms; but it has been most satisfactorily proved that the germ must be present, otherwise no evidence of anything like organization will be developed. All the conditions required for the production of vegetable life appear to show that it is quite impossible for any kind of plant, even the very lowest in the scale, to be formed in any other way than from an embryo in which are contained the elements necessary for it, and the arrangements required for the various processes which are connected with its vitality. The earth is now covered with vegetable life, but there must have existed a time when "darkness was upon the face of the deep," and organization had not yet commenced tracing its lovely net-work of cells upon the bare surface of the oceanburied rock. At length the mystery of organic creation began: into this, science dares not penetrate, but it is privileged to begin its search a little beyond this point, and we are enabled to trace the progress of organic development, through a chain of interesting results which are constantly recurring. If we take some water, rising from a subterranean spring, and expose it to sunshine, we shall see, after a few days, a curious formation of bubbles, and the gradual accumulation of green matter. At first we cannot detect any marks of organization-it appears a slimy cloud of an irregular and undetermined form. It slowly aggregates, and forms a sort of mat over the surface, which at the same time assumes a darker green colour. Careful examination will now show the original corpuscles involved in a net-work formed by slender threads, which are tubes of circulation, and may be traced from small points which we must regard as the compound atom, the vegetable unit. We must not forget, here, that we have to deal with four chemical elements, oxygen, hydrogen, carbon, and nitrogen, which compose the world of organized forms, and that the water affords us the two first as its constituents, gives us carbon in the form of carbonic acid dissolved in it, and that nitrogen is in the air surrounding it, and frequently mixed with it also. Under the influence of sunshine, we have now seen these elements uniting into a mysterious bond, and the result is the formation of a cellular tissue, which possesses many of the functions of the noblest specimens of vegetable growth. But let us examine the progress. The bare surface of a rock rises above the waters covered over with this green slime, a mere veil of delicate net-work, which, drying off, leaves no perceptible trace behind it; but the basis of a mighty growth is there, and under solar influence, in the process of time, other changes occur. After a period, if we examine the rock, we shall find upon its face little coloured cups or lines with small hard discs. These, at first sight, would not be taken for plants, but on close examination they will be found to be lichens. These minute vegetables shed their seed and die, and from their own remains a more numerous crop springs into life. After a few of these changes, a sufficient depth of soil is formed, upon which mosses begin to develop themselves, and give to the stone a second time a faint tint of green, a mere film still, but indicating the presence of a beautiful class of plants, which, under the microscope, exhibit in their leaves and flowers many points of singular elegance. These mosses, like the lichens, decaying, increase the film of soil, and others of a larger growth supply their places, and run themselves the same round of growth and decay. By and by, funguses of various kinds mingle their little globes and umbrella-like forms. Season after season plants perish and add to the soil, which is at the same time increased in depth by the disintegration of the rock over which it is laid, the cohesion of particles being broken up by the operations of vegetable life. The minute seeds of the ferns floating on the breeze, now find a sufficient depth of earth for germination, and their beautiful fronds, eventually, wave in loveliness to the passing winds. Vegetable forms of a higher and a higher order gradually succeed each other, each series perishing in due season, and giving to the soil additional elements for the growth of plants of their own species or those of others. Flowering herbs find a genial home on the once bare rock; and the primrose pale, the purple foxglove, or the gaudy poppy, open their flowers to the joy of light. The shrub, with its hardy roots interlaced through the soil, and binding the very stones, grows rich in its bright greenery. Eventually the tree springs from the soil, and where once the tempest beat on the bare cold rock, is now the lordly and branching monarch of the forest, with its thousand leaves, affording shelter from the storm for bird and beast. Such are the conditions which prevail throughout nature in the progress of vegetable growth; the green matter gathering on a pond, the mildew accumulating on a shaded wall, being the commencement of a process which is to end in the development of the giant trees of the forest, and the beautifully tinted flowers of nature's most chosen spot. PLANTS AND THEIR COUNTRIES. (From the Tract Society's "Geography of Plants.") Spe'cies, n. (see p. 117). Veg'e-ta'tion, n. (L. vegeo), the Lux-u'ri-ant, adj. (L. luxuria), Pro-fuse', adj. (L. pro, fusus, see that are edible, or fit to be eaten, Cul'ti-va'tion, n. (L. cultum, see scent. In-dig'e-nous, adj. (L. in, gigno), native to a country; not exotic. Ver'dure, n. (L. ver), green, the general colour of vegetation in spring. Ex-hale', v. (L. ex, halo), to breathe IT IS estimated that the number of distinct species of plants, already known and described, is 92,930. This includes all the flowering plants, trees, and shrubs, ferns, mosses, lichens, sea and river weeds, (Algae) mushrooms and their allies, (Fungi) in fact, every vegetable production. These are very variously distributed over our globe; light, heat, altitude, soil, situation, all contributing their influence in modifying the diffusion of species, and of these the first two are by far the most important. Near the equator, where light and heat are most intense, vegetation is most luxuriant and profuse; while at the poles, or at those high elevations which reach above the line of perpetual snow, or in the profounder recesses of the ocean, vegetable life seems to become entirely extinct, and not a plant even of the simplest form appears. Between these extreme limits, however, every gradation is seen, according to the increase of latitude or height. The species which inhabit each particular district of our globe are just those best suited to the physical condition of each, and to the requirements of its inhabitants, whether of the human species or of the brute creation. Thus, the water-melon, the banana, the bread-fruit, and the rice-plant, are peculiar to tropical regions; while the vine, wheat, barley, and the common corn-plants, will not succeed in so high a temperature, but require a cooler climate. Many facts, which we shall have to notice, will exhibit to us the goodness of God in so arranging the vegetable productions of our globe, that not only, (to a great extent), are the food-plants of the various countries exactly such as are best adapted to the wants of the inhabitants, but also that a vast variety of the more useful plants are so distributed as to induce commercial intercourse; and thus, while they render nations mutually dependent on one another for many of the comforts and conveniences of life, they are an indirect means of promoting the advancement of civilization, and, above all, of the spread of the gospel. Why, however, a certain species should only be able to flourish in a certain soil, and under a certain amount of heat and moisture, is a problem we cannot as yet solve; it doubtless depends on special peculiarities in the internal structure, but in what those peculiarities consist, we are ignorant. Some plants, too, are very widely distributed. The daisy, for example, is spread throughout Europe almost universally, in Australia, in Northern Asia, in some parts of Africa, and in South America. In India and North America, however, it is entirely absent, and can only be preserved as a choice exotic, tended with the most zealous care in botanic gardens. The cereals, that is, wheat, barley, oats, rye, etc., are endowed with a very great power of adaptation. Though their native country is scarcely known, and they are rarely found wild, yet they possess a power of enduring such a variety of temperature, that they have been introduced by cultivation over a large portion of our globe. They can withstand the cold of 62° N. lat., and though they will not in general bear the heat of the tropics, yet even in such places they are sometimes cultivated during the winter season. The potato, again, though only known wild as a native of the western coast of South America, is now cultivated almost universally, particularly in Europe and North America, and has become one of the most important articles of food, especially among the poor. The On the other hand, many species (and probably the great majority of plants) are very limited in their abodes. Cactus tribe, so generally cultivated in our green-houses, and so remarkable for the singularity of their growth, the absence of leaves, and the splendour of their flowers, contains 800 species, all of which are peculiar to America, and not a single species is a native of Europe, Asia, or Africa. 533 species of the beautiful genus Erica, or heath, are found at or near the Cape of Good Hope, and nowhere else in the world. The species of Cinchona, too, which yield the Peruvian bark, grow only on the eastern declivity of the Andes, as far as 18° s. lat.; and the cedar of Lebanon is indigenous to that mountain alone. It would be easy to multiply instances, but this is needless. These facts will enable us readily to understand, that there are numerous botanical districts on the surface of our globe, each of which has its own vegetation; a considerable number, perhaps the majority of the species, being peculiar to the particular district, while the remaining species are found in various localities. Thus, the Flora of the United States of North America is totally different from that of Europe, even in places where the annual temperature is the same. Of 2,891 species of flowering plants found in the United States, only 385 are common to them and the corresponding latitudes of Europe. In St. Helena, of thirty flowering plants, only one or two are native elsewhere. In the Galapagos1 islands, out of 180 plants which have been collected, 100 are found nowhere else; and 1 Galapagos; a group of islands in the Pacific Ocean, off the Coast of Columbia and immediately under the Equator. |