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In many cases perennial plants, by this change of climate, are converted into annual ones; that is, as if fearing the inclemencies of a cold winter, they pass through their successive stages of existence with rapidity, and accomplish in one summer what they had been accustomed to require years to perform. The nasturtion was originally a shrub, flourishing without cul. tivation on the banks of the Peruvian streams; yet transferred to this country it is an annual plant, which completes its term of existence in a few months.
The habits of some plants are with difficulty subdued ; and it is by slow removals that they can be made to grow in foreign situations. Rice by a slow progress has advanced from Caro. lina to Virginia, and it is now cultivated in New Jersey. The habits of Indian corn, aided by climate and culture, have suf, fered a still more remarkable change. After having been for several years raised in Canada, it arrives to perfection in a few weeks, and on that account is employed by us as an early corn; but that which has been long cultivated in Virginia, will not ripen in a New England summer; yet, originally, the early corn of Canada and that of Virginia were the same, both in habit and other properties.
Agents which affect the growth of plants. Of the various substances by which vegetables are nourish. ed, water is thought the most important. Some plants grow and mature, with their roots immersed in water, without any soil; most of the marine plants are of this description.
Atmospheric air is necessary to the health and vigour of plants; if a plant is placed under a glass into which no air can enter, it withers and dies.
Most plants are found by analysis to contain a certain portion of salts, such as nitre, and muriate of soda,* or common salt. It
appears that the root absorbs them from the soil, by which it is nourished.
No plants can grow without some degree of heat, though some require a greater portion of it than others.
Plants may be made to grow without light, but they will not exhibit the verdure, or any of the properties of health. The atmosphere, which is contaminated by the respiration of ani. mals, is restored to purity by the vegetation of plants; but se. cluded from light, vegetables are no longer capable of converting a portion of the fixed air to their use, or of supplying the atmosphere with the oxygen, on which its importance in sup
According to modern chemistry, chloride of sodium.
Some plants change from perennial to annual-Of rice and Indian corAgents which affect the growth of plants-Water-Atmospheric air-Salts— Heat-Light.
porting animal life chiefly depends. By the action of light, the carbon of the fixed air is interwoven with the texture of the plants. The aromatic plants, the clove, cinnamon, and the Peruvian bark, all owe their chief excellencies to the intense light of the equatorial regions.
Habitations of Plants. Plants are not thrown by chance over the surface of the globe, but we perceive that the Creator has regulated their distribution according to certain fixed principles; we find not only a wonderful adaptation of plants to the physical necessities of animals in general, but that they are also varied to correspond to the peculiar wants of animals in different climates.
First, we would notice the herbs which cover the surface of the earth; had their stems been hard and woody, the greater part of the earth would have been inaccessible to the foot of man, until the vegetation was first destroyed by fire, or by some other means. Shall we suppose that the grass and herbs which now afford a soft carpet for our feet, came by chance to grow “thus, rather than hard and woody like the trees ? Shall we suppose, too, that by chance, the prevailing colour of vegetation is green, that colour upon which, above all, the eye rests with the most agreeable sensations ? Suppose the grass and herbs to have been red or yellow, and with our present organs of sight, how painful would be the sensations excited by these bright colours ! Instead of beholding nature with delight, we should turn from it, and vainly seek some object on which the eye might repose.
Woody shrubs occasionally alternate with herbs, but they are so placed as not to offer obstructions to the foot of man; they often grow out of the clefts of rocks, affording a means of climbing almost perpendicular precipices. Large trees are not usually placed so near together as to prevent a passage between them; their lowest branches are mostly at a height sufficient to admit men and beasts under them, and thus, few fo. rests are impenetrable.
In cold countries, whether occasioned by distance from the equator, or elevation by means of mountains and table lands, we find the pine, fir, and cedar, and other resinous plants, which furnish man, during the dreary season of winter, with light and fuel. The leaves of these trees are mostly filiform, or long and narrow, thus fitted for reverberating the heat, like the hair of animals, and for resisting the impetuosity of winds, which often prevail in those regions.
In warm countries, trees present in their foliage a resource
Habitations of Plants—Herbs-Woody shrubs Trees—Trees of cold countries–Of warm countries.
from the scorching rays of the sun; their leaves serving as fans and umbrellas. The leaf of the banana is broad and long, like an apron; it has acquired the name of Adam's fig leaf. The leaves of the cocoa tree are said to be from twelve to fifteen feet long, and from seven to eight broad. Those of the talipot tree are equal in size. A traveller remarks respecting the leaves of the talipot tree, that one is capable of covering
from fifteen to twenty persons. The soldiers, he says, use it for a covering to their tents. He remarks, that it seems an inestimable blessing of Providence in a country burnt up by the sun, and inundated by rains for six months of the year. In our climate, during the warm season, Providence bestows upon us a variety of juicy and acid fruits, cherries, peaches, plums, me. lons and berries; nuts and many fruits are fitted for preserva. tion during the winter, so that we are never destitute of these bounties.
A remarkable instance of the care of Providence in provi. ding for the wants of man, appears in what is related of a plant found amidst the burning deserts of Africa ; the leaf of which is said to be in the form of a pitcher, and to possess the property of secreting moisture to such a degree as to form a quantity of water sufficient for a draught to a thirsty person ;* the end of the leaf is folded over the throat, as if to prevent the evaporation of the fluid.t Various plants and trees, in hot regions, furnish refreshing draughts to the thirsty traveller.
These remarks might be pursued to an extent as great as the vastness of the vegetable kingdom, and wants of man; we have merely glanced at the subject of the adaptation of plants to the wants of animal life, hoping that these few suggestions may lead you to trace, from your own observation of the works of na. ture, the great designing mind, which rules and governs all with infinite wisdom and benevolence.
The earth, then, we find to be covered with a multitude of species of plants, differing not more by their external forms, than by their internal structure, each endowed with peculiar habits and instincts.
Some species seem adapted to the mountains, some to the valleys, and others to the plains; some require an argillaceous or clayey soil, others a calcareous soil, or one impregnated with lime; others a quartzose or sandy soil, and some will only grow where the earth contains soda or marine salts. Many
* This plant, from the general description of the leaf, would seem to be the Sarracenia; this, however, only grows in marshes.
+ See Part I.
A plant found in the deserts of Africa-Reflection-Plants adapted to various soils, &c.
plants will grow only in water; we find here such as are peculiar to the marsh, the lake, the river, and the sea. Many plants require a very elevated temperature, some will grow only in mild and temperate climates, and others only in the midst of frosts and snows.
Thus every country where man is to be found has its vegetation. Some species of plants, with respect to localities, are confined to narrow limits.
A species of ORIGANUM (the tournefortii), was discovered by Tournefort, in 1700, upon one single rock'in the little island of Amorgos, in the Greek Archipelago; eighty years afterwards the plant was found in the same island, and upon the same rock, and has never been discovered in any other situation. Some plants confine themselves within certain longitudes, scarcely varying from the right to the left. The MENZIESIA pallifolia, a species of heath confined between ten and fifteen degrees of west longitude, is found in Portugal, Spain, and Ireland. Lati. tude and elevation, by reason of mountains and table lands, produce a greater variety in the appearance of vegetation than almost any other causes.
Few plants are found to endure extreme cold. Botanists have estimated, that at Spitsbergeri
, in north latitude about 80°, there are but about 30 species of plants ; in Lapland, in 70°, there are 539 species; at Madagascar, at the tropic of Capricorn, there are 5000; and at the equator a much greater num. ber. These estimates fall very far short of the number of species now known, but they may give some idea of the differ. ence in the vegetation of cold and warm climates.
Geographical situation of Plants. Every country exhibits a botanical character peculiar to itself. Linnæus, in his bold and graphic language, said,* “ A practical botanist can usually at the first glance, distinguish the plants of Africa, Asia, America and the Alps; but it is not easy to tell how he is able to do this. There is a certain cha. racter of sullenness, gloom and obscurity, in the plants of Africa; something proud and elevated in those of Asia ; joyful and smiling in those of America ; while those of the Alps seem hardened and ungrateful!".
In investigating the geographical situation of the vegetable * Primo intuitu distinguit sæpius exercitatus botanicus plantas Africæ, Asiæ, Americæ, Alpiumque, sed non facile dicerit ipse ex qua nota. Nescis quæ facies torva, sicca, obscuris Afris ; quæ superba, exaltata Asiaticus ; quæ laota, glabra Americanus ; quæ coarctata, indurata Alpinis !
Some have a confined locality-Few endure extreme cad- Every country has its own botanical character.
kingdom, we see the powerful effects of light and heat. Feeble in the polar regions, vegetation acquires strength as we approach towards the equator, where the light of the sun is vivid, and its heat, permanent and intense.
The centre of the frigid zone is entirely destitute of vegeta. tion. After passing the arctic circle, we find on the borders of the temperate zone, a few species of plants, chiefly lichens, mosses, and ferns, also a few shrubs and berries. In the heat of a polar summer, the growth of plants is rapid ; Lapland is the only country within this zone where any kind of grain can be raised.
The productions of the temperate zone gradually alter in character as we approach the tropics. Humboldt has divided the temperate zone, with respect to productions, into three regions; the cold, the temperate, and warm regions. In the cold region, grain may be raised to advantage, and berries grow in abundance. In the temperate region, the wine grape, grain, and fruits of many kinds, are cultivated in their greatest perfection. The warm region produces olives, figs oranges and lemons.
The variety of plants in the torrid zone is very great. Trees are more numerous in proportion to other plants, than in the temperate zones; the same tribes which are there slender and humble plants, here spread into lofty trees, many of which are adorned by large and beautiful flowers. The richest fruits and spices, and the most valuable medicinal plants are found here. In ascending the mountains of the torrid zone, as the temperature varies, each section has its own distinct plants, and we find in succession, the production of every region from the equator to the poles.*
As the mountains of the torrid zone afford every yariety of climate between their base and their summit, so they are capable of producing all the vegetables of every climate ; but as the temperature diminishes, as the latitude increases, so, generally speaking, the productions, as we proceed from the tropic northward or southward, correspond with the elevation at which the same plants will grow upon a mountain within the tropics. Every plant requires other circumstances alike; the same mean annual temperature,† for example. The magnifi. cent plantain tree and valuable sugar cane require a mean annual heat of from 82 to 73 degrees; but 73 degrees of mean
So Frontispiece. + explanation of mean annual temperature, see note under vines, Lecture
Plants of the frigid zone-Temperate zone – Torrid zone- e-Production of every region found in ascending mountains of the torrid zone.