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few pores on the epidermis, evaporate but little moisture from their surface, as the succulent tribe.

1739. The qualities of water, or the nature of the substances dissolved in it, must necessarily influence powerfully the possibility of certain plants growing in certain places. But the difference in this respect is much less than would be imagined, because the food of one species of plant differs very little from that of another. The most remarkable case is that of salt marshes, in which a great many vegetables will not live, whilst a number of others thrive there better than any where else. Plants which grow in marine marshes, and those which grow in similar grounds situated in the interior of a country, are the same. Other substances naturally dissolved in water appear to have much less influence on vegetation, though the causes of the habitations of some plants, such as those which grow best on walls, as Peltària, and in lime-rubbish, as Thláspi, and other Cruciferæ, may doubtless be traced to some salt (nitrate of lime, &c.) or other substance peculiar to such situations.

1740. The nature of the earth's surface affects the habitations of vegetables in different points of view: 1. As consisting of primitive earths, or the débris of rocks or mineral bodies; and, 2. As consisting of a mixture of mineral, animal, and vegetable matter. 1741. Primitive surfaces affect vegetables mechanically according to their different degrees of movability or tenacity. On coarse sandy surfaces plants spring up easily; but many of them, which have large leaves or tall stems, are as easily blown about and destroyed. On fine, dry, sandy surfaces, plants with very delicate roots, as Pròtea and Erica, prosper; a similar earth, but moist in the growing season, is suited to bulbs. On clayey surfaces plants are more difficult to establish, but when established are more permanent: they are generally coarse, vigorous, and perennial in their duration.

1742. With respect to the relative proportions of the primitive earths in these surfaces, it does not appear that their influence on the distribution of plants is so great as might at first sight be imagined. Doubtless different earths are endowed with different degrees of absorbing, retaining, and parting with moisture and heat; and these circumstances have a material effect in a state of culture, where they are comminuted and exposed to the air; but not much in a wild or natural state, where they remain hard, firm, and covered with vegetation. The difference, with a few exceptions, is never so grer but that the seeds of a plant which has been found to prosper well in one description of earth, will germinate and thrive as well in another composed of totally different earths, provided they are in a nearly similar state of mechanical division and moisture. Thus, Decandolle observes, though the box is very common on calcareous surfaces, it is found in as great quantities in such as are schistous or granitic. The chestnut grows equally well in calcareous and clayey earths, in volcanic ashes, and in sand. The plants of Jura, a mountain entirely calcareous, grow equally well on the Vosges or the granitic Alps. But though the kind or mixture of earths seems of no great consequence, yet the presence of metallic oxides and salts, as sulphates of iron or copper, or sulphur alone, or alum, or other similar substances in a state to be soluble in water, are found to be injurious to all vegetation, of which some parts of Derbyshire and the maremmes of Tuscany (Chateauvieux, let. 8.) are striking proofs. But except in these rare cases, plants grow with nearly equal indifference on all primitive surfaces, in the sense in which we here take these terms; the result of which is, that earths, strictly or chemically so termed, have much less influence on the distribution of plants than temperature, elevation, and moisture. Another result is, as Decandolle has well remarked, that it is often a very bad method of culture, to imitate too exactly the nature of the earth in which a plant grows in its wild

state.

1743. Mixed or secondary soils include not only primitive earths, or the débris of rocks, but vegetable matters; not only the medium through which perfect plants obtain their food, but that food itself. In this view of the subject the term soil is used in a very extensive acceptation, as signifying, not only the various sorts of earths which constitute the surface of the globe, but every substance whatever on which plants are found to vegetate, or from which they derive their nourishment. The obvious division of soils, in this acceptation of the term, is that of aquatic, terrestrial, and vegetable soils; corresponding to the division of aquatic, terrestrial, and parasitical plants.

1744. Aquatic soils are such as are either wholly or partially inundated with water, and are fitted to produce such plants only as are denominated aquatics. Of aquatics there are several subdivisions according to the particular situations they affect, or the degree of immersion they require.

1745. One of the principal subdivisions of aquatics is that of marine plants, such as the Faci and many of the Algae, which are very plentiful in the scas that wash the coasts of Great Britain, and are generally attached to the stones and rocks near the shore. Some of them are always immersed; and others, which are situated above low-water mark, are immersed and exposed to the action of the atmosphere alternately. But none of them can be made to vegetate except in the waters of the sea. Another subdivision of aquatics is that of river plants, such as Chara, Potamogeton, and Nymphæ'a, which occupy the beds of freshwater rivers, and vegetate in the midst of the running stream; being for the most part wholly immersed, as well as found only in such situations.

1746. A third subdivision of aquatics is that of paludal or fen plants, being such as are peculiar to lakes, marshes, and stagnant or nearly stagnant waters, but of which the bottom is often tolerably clear. In such situations you find the Isoètes lacustris, flowering rush, water ranunculus, water violet, and a variety of others, which uniformly affect such situations; some of them being wholly immersed, and others immersed only in part.

1747. Earthy soils are such as emerge above the water, and constitute the surface of the habitable globe, which is every where covered with vegetable productions. Plants affecting such soils, which comprise by far the greater part of the vegetable kingdom, are denominated terrestrial, being such as vegetate upon the surface of the earth, without having any portion immersed in water, or requiring any further moisture for their support beyond that which they derive from the earth and atmosphere. This division is, like the aquatics, distributed into several subdivisions according to the peculiar situations which different tribes affect.

1748. Some of them are maritime, that is, growing only on the sea-coast, or at no great distance from it, such as Státice, Glaúx, Samòlus, samphire, sea-pea.

1749. Some are furiatic, that is, affecting the banks of rivers, such as Lythrum, Lycopus, Eupatorium. 1750. Some are champaign, that is, affecting chiefly the plains, meadows, and cultivated fields, such as Cardamine, Tragopogon, Agrostémma.

1751. Some are dumose, that is, growing in hedges and thickets, such as the bramble.

1752. Some are ruderate, that is, growing on rubbish, such as Senecio viscosus.

véstris.

1753. Some are sylvatic, that is, growing in woods or forests, such as Stachys sylvática, Angélica syl1754. And, finally, some are alpine, that is, growing on the summits of mountains, such as Pòa alpina, Epilobium alpinum, and many of the mosses and lichens.

1755. Vegetable soils are such as are formed of vegetating or decayed plants themselves, to some of which the seeds of certain other plants are found to adhere, as being the only soil fitted to their germination and developement. The plants springing from them are denominated Parasitical, as being plants that will vegetate neither in the water nor earth, but on certain other plants, to which they attach themselves by means of roots, that penetrate the bark, and from the juices of which they do often, though not always, derive their support. This last circumstance constitutes the ground of a subdivision of parasitical plants, into such as adhere to the dead or inert parts of other plants, and such as adhere to living plants, and feed on their juices.

1756. In the first subdivision we may place parasitical mosses, lichens, and fungi, which are found as often, and in as great perfection, on the stumps of rotten trees, and on rotten pales and stakes, as on trees which are yet vegetating; whence it is also plain that they do not derive their nourishment from the juices of the plants on which they grow, but from their decayed parts, and the atmosphere by which they are surrounded; the plant to which they cling serving as a basis of support.

1757. In the second subdivision we may place all plants strictly parasitical, that is, all such as do actually abstract from the juices of the plant to which they cling the nourishment necessary to the developement of their parts; and of which the most common, at least as being indigenous to Britain, are the mistletoe, dodder, broom-rape, and a sort of tuber which grows on the root of saffron, and destroys it if allowed to spread.

1758. The mistletoe (Viscum álbum) is found for the most part on the apple tree; but sometimes also on the oak. If its berry is made to adhere to the trunk or branch of either of the foregoing trees, which from its glutinous nature it may readily be made to do, it germinates by sending out a small globular body attached to a pedicle, which after it acquires a certain length bends towards the bark, whether above it or below it, into which it insinuates itself by means of a num ber of small fibres which it now protrudes, and by which it abstracts from the plant the nourishment necessary to its future developement. When the root has thus fixed itself in the bark of the supporting tree, the stem of the para site begins to ascend, at first smooth and tapering, and of a pale green colour, but finally protruding a multiplicity of branches and leaves. It seems to have been thought by some botanists that the roots of the mistletoe penetrate even into the wood, as well as through the bark. But the observations of Du Hamel show that this opinion is not well founded. The roots are, indeed, often found within the wood, which they thus seem to have penetrated by their own vegetating power: but the fact is, that they are merely covered by the additional layers of wood which have been formed since the fibres first insinuated themselves into the bark.

1759. The Cuscuta europea, or dodder (fig. 200.), though it is to be accounted a truly parasitical plant in the issue, is yet not originally so. For the seed of this plant, when it has fallen to the ground, takes root originally by sending down its radicle into the soil and elevating its stem into the air. It is not yet, therefore, a parasitical plant. But the stem which is now elevated above the surface lays hold of the first plant it meets with, though it is particularly partial to hops and nettles, and twines itself around it, attaching itself by means of little parasitical roots, at the points of contact, and finally detaching itself from the soil altogether by the decay of the original root, and becoming a truly parasitical plant. Withering describes the plant in his Arrangement as being originally parasitical; but this is certainly not the fact.

1760. The Orobanche, or broom-rape, which attaches itself by the root to the roots of other plants, is also to be regarded as being truly parasitical, though it sometimes sends out fibres which seem to draw nourishment from the earth. It is found most frequently on the roots of clover and common broom, but also in various other places.

1761. The Epidendrum fós deris is regarded also by botanists as a parasitical plant, because it is generally found growing on other trees. But as it is found to grow in old tan, it probably derives only support from the bark of trees, and not nourishment.

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tables, and some, also, on their habitation. The Fungi do not require the usual intervention of day, in order to decompose carbonic acid gas, and can live and thrive with little or no light. In green plants, which require the action of light, the intensity requisite is very different in different species; some require shady places, and hence the vegetable inhabitants of caves, and the plants which grow in the shades of forests; others, and the greater number, require the direct action of the sun, and grow in exposed, elevated sites. Decandolle considers that the great difficulty of cultivating alpine plants in the gardens of plains, arises from the impossibility of giving them at once the fresh temperature and intense light which they find on high mountains.

SECT. III. Civil Causes affecting the Distribution of Plants.

1763. By the art of man plants may be inured to circumstances foreign from their usual habits. Though plants in general are limited to certain habitations destined for them by nature, yet some are, and probably the greater number may be, inured to climates, soils, and situations, of which they are not indigenous. The means used are acclimation and culture.

1764. Acclimation seems to be most easily effected in going from a hot to a cold climate, particularly with herbaceous plants; because it often happens that the frosts of winter are accompanied with snow, which shelters the plant from the inclemency of the atmosphere till the return of spring. Trees and shrubs, on the contrary, are acclimated with more difficulty, because they cannot be so easily sheltered from the colds, owing to the greater length of their stems and branches. The acclimation, or naturalisation of vegetables has been attempted by two modes: by sowing the seeds of successive generations, and by the difference of temperature produced by different aspects. But though the habits of individuals may be altered by what is called acclimation, that is, by diminishing or increasing the supplies of nourishment and of heat, yet no art or device of man will alter the nature of the species. The potato, the kidneybean, the nasturtium, georgina, and many other plants which have been long in culture in Europe, and propagated from seeds ripened there through innumerable generations, there is no reason to suppose are in the least degree more hardy than when first imported from Asia or South America. The same slight degree of autumnal frost blackens their leaves, and of spring cold destroys their germinating seeds. But as summer is nearly the same thing in all lands, the summer or annual plants of the tropics are made to grow in the summers of the temperate zones, and, indeed, in general, the summer plants of any one country will grow in the summer climate of any other. The cucumber is grown in the fields in Egypt, and near Petersburg.

1765. Domesticated plants. "Some plants," Humboldt observes, "which constitute the object of gardening and of agriculture, have time out of mind accompanied man from one end of the globe to the other. In Europe the vine followed the Greeks; the wheat, the Romans; and the cotton, the Arabs. In America, the Tultiques carried with them the maize; and the potato and quinoa (Chenopòdium Quinda, of which the seeds are used) are found wherever have migrated the ancient Condinamarea. The migration of these plants is evident; but their first country is as little known as that of the different races of men, which have been found in all parts of the globe from the earliest traditions." (Géographie des Plantes, p. 25.)

1766. The general effect of culture on plants is that of enlarging all their parts; but it often also alters the qualities, forms, and colours: it never, however, alters their primitive structure. "The potato," as Humboldt observes, "cultivated in Chile, at nearly twelve thousand feet above the level of the sea, carries the same flower as in Siberia."

1767. The culinary vegetables of our gardens, compared with the same species in their wild state, afford striking proofs of the influence of culture on both the magnitude and qualities of plants. Nothing in regard to magnitude is more remarkable than in the case of the Brássica tribe; and nothing, in respect to quality, exceeds the change effected on the celery, the carrot, and the lettuce.

1768. The influence of culture on fruits is not less remarkable. The peach, in its wild state in Media, is poisonous; but cultivated in the plains of Ispahan and Egypt, it becomes one of the most delicious of fruits. The effect of culture on the apple, pear, cherry, plum, and other fruits, is nearly as remarkable; for not only the fruit and leaves, but the general habits of the tree, are altered in these and other species. The history of the migration of fruit trees has been commenced by Sickler, in a work (Geschichte, &c.) which Humboldt has praised as equally curious and philosophical.

1769. The influence of culture on plants of ornament is great in most species. The parts of all plants are enlarged; some are numerically increased, as in the case of double flowers; and, what is most remarkable, even the colours are frequently changed, in the leaf, flower, and fruit.

1770. The influence of civilisation and culture, in increasing the number of plants in a country, is very considerable, and operates directly, by introducing new species for cul

ture in gardens, fields, or timber-plantations; and indirectly by acclimation and final naturalisation of many species, by the influence of winds and birds in scattering their seeds. The vine and the fig are not indigenous to France, but are now naturalised there by birds. In like manner the orange is naturalised in the south of Italy. Many plants of the Levant are naturalised both in France and Britain; some, as the cabbage, cherry, and apple, were probably naturalised in England during its subjection to the Romans. The narrow-leaved elm was brought from the Holy Land during the crusades. Phaseolus vulgàris and Impatiens Balsamina were brought originally from India; and, Datura Stramonium, which is now naturalised in Europe, was brought originally from India or Abyssinia. Buckwheat and most species of corn and peas came also from the East, and along with them several plants found among corn only, such as Centaurèa Cyanus, Agrostémma Githago, Ráphanus Raphanistrum, and Myagrum sativum. The country whence the most valuable grasses migrated is not known. Bruce says he found the oat wild in Abyssinia, and wheat and millet have been found in a wild state in hilly situations in the East Indies. Rye and the potato were not known to the Romans. The country of the former Humboldt declares to be totally unknown.

1771. The greatest refinement in culture consists in the successful formation of artificial climates, for the culture of tropical plants, in cold regions. Many vegetables, natives of the torrid zone, as the pine apple, the palm, &c., cannot be acclimated in temperate countries: but by means of hot-houses of different kinds, they are grown, even on the borders of the frozen zone, to the highest degree of perfection; and, in Britain, some of the tropical fruits, as the pine and melon, are brought to a greater size and better flavour than in their native habitations. Casting our eyes on man, and the effects of his industry, we see him spread on the plains and sides of mountains, from the Frozen Ocean to the equator, and every where wishing to assemble around him whatever is useful and agrecable of his own country or those of others. The more difficulties to surmount, the more rapidly are developed the moral faculties; and thus the civilisation of a people is almost always in an inverse ratio with the fertility of the soil which they inhabit. What is the reason of this? Humboldt asks. Habit and the love of native land.

SECT. IV. Characteristic or Picturesque Distribution of Vegetables.

1772. The social and antisocial habits of plants are their most remarkable characteristics. Like animals, they live in two classes: the one class grows alone and scattered, as Solànum Dulcamàra, Lýchnis dioica, Polygonum Bistórta, Anthéricum Liliàgo, &c.; the other class unites in society, like ants or bees, covers immense surfaces, and excludes other species, such as Fragaria vésca, Vaccinium Myrtillus, Polygonum aviculàre, Aira canéscens, Pinus sylvestris, &c. Barton states that the Mitchella rèpens is the plant most extensively spread in North America, occupying all the ground between the 28° and 69° of north latitude; that the Arbutus ùva úrsi extends from New Jersey to the 72° of north latitude; while, on the contrary, Gordònia, Franklínia, and Dione'a muscípula are found isolated in small spots. Associated plants are more common in the temperate zones than in the tropics, where vegetation is less uniform and more picturesque. In the temperate zones, the frequency of social plants, and the culture of man, have rendered the aspect of the country comparatively monotonous. Under the tropics, on the contrary, all sorts of forms are united; thus cypresses and pines are found in the forests of the Andes of Quindiu and of Mexico; and bananas, palms, and bamboos in the valleys (fig. 201.):

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but green meadows and the season of spring are wanting, for nature has reserved gifts for every region. "The valleys of the Andes," Humboldt observes, "are ornamented

brambles, and a crowd of genera believed to belong only to countries of the north. Thus the inhabitant of the equinoctial regions views all the vegetable forms which nature has bestowed around him on the globe. Earth developes to his eyes a spectacle as varied as the azure vault of heaven, which conceals none of her constellations." The people of Europe do not enjoy the same advantage. The languishing plants, which the love of science or luxury cultivates in our hot-houses, present only the shadow of the majesty of equinoctial vegetation; but, by the richness of our language, we paint these countries to the imagination, and cultivated man feels a happiness peculiar to civilisation. 1773. The features of many plants are so obvious and characteristic, as to strike every general observer. The Scitamíneæ, tree-heaths, firs and pines, Mimòsæ, climbers, Cácti, grasses, lichens, mosses, palms, Equisetaceæ, Malvàceæ, Aröideæ, Orchideæ, Liliacea, &c., form remarkable groups distinguishable at first sight. Of these groups, the most beautiful are the palms, Scitamineæ, and Liliàceæ, which include the bamboos and plantains, the most splendid of umbrageous plants.

1774. The native countries of plants may often be discovered by their features, in the same manner as the national distinctions which are observable in the looks and colour of mankind, and which are effected chiefly by climate. Asiatic plants are remarkable for their superior beauty; African plants for their thick and succulent leaves, as in the case of the Cacti ; and American plants for the length and smoothness of their leaves, and for a sort of singularity in the shape of the flower and fruit. The flowers of European plants are but rarely beautiful, a great portion of them being amentaceous. Plants indigenous to polar and mountainous regions are generally low, with small compressed leaves; but with flowers large in proportion. Plants indigenous to New Holland are distinguishable by small and dry leaves, which have often a shrivelled appearance. In Arabia they are low and dwarfish; in the Archipelago they are generally shrubby and furnished with prickles; while, in the Canary Islands, many plants, which, in other countries, are merely herbs, assume the port of shrubs and trees. The shrubby plants of the Cape of Good Hope and New Holland exhibit a striking similarity. The shrubs and trees of the northern parts of Asia and America also are very much alike; which may be exemplified in the Plátanus orientalis of the former, and in the Plátanus occidentàlis of the latter, as well as in Fagus sylvatica and Fàgus latifòlia, or Acer cappadòcium and Acer saccharinum; and yet the herbs and undershrubs of the two countries do not in the least correspond. "A tissue of fibres," Humboldt observes, "more or less loose, vegetable colours more or less vivid, according to the chemical mixture of their elements, and the force of the solar rays, are some of the causes which impress on the vegetables of each zone their characteristic features."

1775. The influence of the general aspect of vegetation on the taste and imagination of a people; the difference in this respect between the monotonous oak and pine forests of the temperate zones, and the picturesque assemblages of palms, mimosas, plantains, and bamboos of the tropics; the influence of the nourishment, more or less stimulant, peculiar to different zones, on the character and energy of the passions; these, Humboldt observes, unite the history of plants with the moral and political history of man.

SECT. V. Systematic Distribution of Vegetables.

1776. The distribution of plants, considered in respect to their systematic classifications, is worthy of notice. The three grand systematic divisions of plants are Acotyledoneæ, Dicotyledoneæ, and Monocotyledoneæ. A simplification of this division considers plants as agamous or phanerogamous, that is, without or with visible sexes.

1777. Plants of visible sexes. Taking the globe in zones, the temperate contain the greater part of all the phanerogamous or visible sexual species of plants. The equinoctial countries contain nearly, and Lapland only part.

1778. Plants with the sexual parts invisible or indistinct. Taking the whole surface of the globe, the agamous plants, that is, Músci, Fúngi, Fùci, &c., are to the phanerogamous or perfect plants, nearly as 1 to 7; in the equinoctial countries as 1 to 5; in the temperate zones, as 2 to 5; in New Holland, as 2 to 11; in France, as 1 to 2; in Lapland, Greenland, Iceland, and Scotland, they are as 1 to 1, or even more numerous than the phanerogamous plants. Within the tropics, agamous plants grow only on the summits of the highest mountains. In several of the islands of the Gulf of Carpentaria, having a Flora of phanerogamous plants exceeding 200 species, R. Brown did not observe a single moss.

1779. In the whole globe, the Monocotyledoneæ, including the Gramíneæ, Liliaceæ, Scitamíneæ, &c., are to the whole of the perfect plants as 1 to 6; in the temperate zones (between 36 and 52°,) as one to 4; and in the polar regions as 1 to 20. In Germany, the Monocotyledoneæ are to the total number of species as 1 to 4; in France as 1 to 43; in New Holland the three grand divisions of plants, beginning with the Acotyledòneæ, are nearly as 1, 24, and 74.

1780. Dicotyledonea. In the whole globe, the Monocotyledoneæ are estimated by

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