which, as they float in the air, enter the pores of the epidermis of the leaf, particularly if the plant is sickly; or they exist in the manure or soil, and enter by the pores of the root. (Sir J. Banks on Blight, 1805.) This fungus has been figured by Sowerby, and by F. Bauer, and Grew. It is known among farmers by the name of red rust, and as it affects the stalks and leaves only it does not materially which the crop. But there is another species of fungus known to the farmer by the name of red gum, injure attacks the ear only, and is extremely prejudicial. In the aggregate it consists of groups of minute globules interspersed with transparent fibres. The globules are filled with a fine powder, which explodes when they are put into water. It is very generally accompanied with a maggot of a yellow colour, that preys also upon the grain, and increases the amount of injury. The only means of preventing or lessening the effect of any of the different varieties of blight mentioned is proper culture. Palliatives are to be found in topical applications, such as flower of sulphur, and where the disease proceeds from, or consists of, innumerable minute insects, it may occasionally be removed. Grisenthwaite conjectures that in many cases in which the blight and mildew attack corn-crops, it may be for want of the peculiar food requisite for perfecting the grain; it being known that the fruit or seeds of many plants contain primitive principles not found in the rest of the plant. Thus the grain of wheat contains gluten and phosphate of lime, and where these are wanting in the soil, that is, in the manured earths in which the plant grows, it will be unable to perfect its fruit, which of consequence becomes more liable to disease. (New Theory of Agr. &c.)

1658. Smut is a disease incidental to cultivated corn, by which the farina of the grain, together with its proper integuments and even part of the husk, is converted into a black soot-like powder. If the injured ear is struck with the finger, the powder will be dispersed like a cloud of black smoke; and if a portion of the powder is wetted by a drop of water and put under the microscope, it will be found to consist of millions of minute and transparent globules, which seem to be composed of a clear and glary fluid encompassed by a thin and skinny membrane. This disease does not affect the whole body of the crop, but the smutted ears are sometimes very numerously dispersed throughout it. Some have attributed it to the soil in which the grain is sown, and others have attributed it to the seed itself, alleging that smutted seed will produce a smutted crop. But in all this there seems to be a great deal of doubt. Willdenow regards it as originating in a small fungus, which multiplies and extends till it occupies the whole ear. (Princip. of Bot. p. 356.) But F. Bauer of Kew, seems to have ascertained it to be merely a morbid swelling of the ear, and not at all connected with the growth of a fungus. (Smith's Introd. p. 348.) It is said to be prevented by steeping the grain before sowing in a weak solution of arsenic. But besides the disease called smut there is also a disease analogous to it, or a different stage of the same disease, known to the farmer by the name of bags or smut-balls, in which the nucleus of the seed only is converted into a black powder, whilst the ovary, as well as the husk, remains sound. The ear is not much altered in its external appearance, and the diseased grain contained in it will even bear the operation of threshing, and consequently mingle with the bulk. But it is always readily detected by the experienced buyer, and fatal to the character of the sample. It is said to be prevented as in the case of smut.

1659. Mildew is a thin and whitish coating with which the leaves of vegetables are sometimes covered, occasioning their decay and death, and injuring the health of the plant. It is frequently found on the leaves of tussilago farfara, humulus lupulus, corylus avellana, and the white and yellow dead-nettie. It is found also on wheat in the shape of a glutinous exudation, particularly when the days are hot and the nights without dew. Willdenow says it is occasioned by the growth of a fungus of great minute. ness, the mucor erisyphe of Linnæus; or by a sort of whitish slime which some species of aphides deposit upon the leaves. J. Robertson (Hort. Trans. v. 178.) considers it as a minute fungus of which different species attack different plants. Sulphur he has found the only specific cure. In cultivated crops mildew is said to be prevented by manuring

with soot.

1660. Honey-dew is a sweet and clammy substance which coagulates on the surface of the leaves during hot weather, particularly on the leaves of the oak-tree and beech, and is regarded by Curtis, as being merely the dung of some species of aphides. This seems to be the opinion of Willdenow also, and it is no doubt possible that it may be the case in some instances or species of the disease. But Sir J. E. Smith contends that it is not always so, or that there are more species of honey-dew than one, regarding it particularly as being an exudation, at least in the case of the beech, whose leaves are, in consequence of an unfavorable wind, apt to become covered with a sweet sort of glutinous coating, similar in flavor to the fluid obtained from the trunk.

1661. It is certain, however, that saccharine exudations are found on the leaves of many plants, though not always distinguished by the name of honey-dew; which should not perhaps be applied except when the exudation occasions disease. But if it is to be applied to all saccharine exudations whatever, then we must include under the appellation of honey-dew, the saccharine exudations observed on the orange-tree by De la Hire, together with that of the lime-tree which is more glutinous, and of the poplar which is more resinous; as also that of the cistus ereticus, and of the manna which exudes from the ash-tree of Italy and larch of France. It is also possible that the exudation or excrement constituting honey-dew may occasionally occur without producing discase; for if it should happen to be washed off soon after by rains or heavy dews, then the leaves will not suffer. Washing is therefore the palliative: judicious culture the preventive.

1662. Dropsy. Plants are also liable to a disease which affects them in a manner similar to that of the dropsy in animals, arising from long continued rain or too abundant watering.

Willdenow describes it as occasioning a preternatural swelling of particular parts, and inducing putrefaction. It is said to take place chiefly in bulbous and tuberous roots, which are often found much swelled after rain. It affects fruits also, which it renders watery and insipid. It prevents the ripening of seeds, and occasions an immoderate production of roots from the stem.

1633. Succulent plants. This disease generally appears in consequence of excessive waterings, and is generally incurable. The leaves drop, even though plump and green; and the fruit rots before reaching maturity. In this case the absorption seems to be too great in proportion to the transpiration; but the soil when too much manured produces similar effects. Du Hamel planted some elms in a soil that was particularly well manured, and accordingly they pushed with great vigor for some time; but at the end of five or six years they all died suddenly. The bark was found to be detached from the wood, and the cavity filled up with a reddish-colored water. The symptoms of this disease suggest the palliatives; and the preventive is ever the same-judicious culture.

1664. Flux of juices. Some trees, but particularly the oak and birch, are liable to a great loss of sap either bursting out spontaneously, owing to a superabundance of sap, or issuing from accidental wounds; sometimes it is injurious to the health of the plant, and sometimes not.

1665. There is a spontaneous extravasation of the sap of the vine, known by the name of the tears of the wine, which is not always injurious. As it often happens that the root imbibes sap, which the leaves are not yet prepared to throw off, because not yet sufficiently expanded, owing to an inclement season, the sap which is first carried up, being propelled by that which follows, ultimately forces its way through all obstructions, and exudes from the bud. But this is observed only in cold climates; for in hot climates where the developement of the leaves is not obstructed by cold, they are ready to elaborate the sap as soon as it reaches them. There is also a spontaneous extravasation of proper juice in some trees, which does not seem in general to be injurious to the individual. Thus the gum which exudes from cherry, plum, peach, and almond trees, is seldom detrimental to their health, except when it insinuates itself into the other ressels of the plant and occasions obstructions.

1606. But the crudation of gum is sometimes a disease, and one for which there is seldom any remedy. It is generally the consequence of an unsuitable soil, situation, or climate. Cold raw summers will produce it in the peach, apricot, and more under-sorts of plum and cherry; or grafting these fruits on diseased stocks. Cutting out the part and applying a covering of loam or tar and charcoal to exclude the air are palliatives; but the only effectual method, where it can be practised, is to take up the tree and place it in a suitable soil and situation.

1607. The extravasation and corruption of the ascending or descending juices, has been known to occasion a fissure of the solid parts. Sometimes the fissure is occasioned by means of frost, forming what is called a double alburnum; that is, first a layer that has been injured by the frost, and then a layer that passes into wood. Sometimes a layer is partially affected, and that is generally owing to a sudden and artial thaw on the south side of the trunk, which may be followed again by a sudden frost. In this case the alburnum is split into clefts or chinks, by means of the expansion of the frozen sap.

1668, Chilldains. But clefts thus occasioned often degenerate into chilblains that discharge a blackish and acrid fluid to the great detriment of the plant, particularly if the sores are so situated that rain or snow will readily lodge in them, and become putrid. The same injury may be occasioned by the bite or puncture of insects while the shoot is yet tender; and as no vegetable ulcer heals up of its own accord, the sooner a cure is attempted the better, as it will, if left to itself, ultimately corrode and destroy the whole plant, bark, wood, and pith. The only palliative is the excision of the part affected, and the application of a cost of grafting wax. (Willdenow, p. 354.)

1669. Gangrene. Of this disorder there are two varieties, the dry and the wet. The former is occasioned by means of excessive heat or excessive cold. If by means of cold, it attacks the leaves of young shoots and causes them to shrink up, converting them from green to black; as also the inner bark, which it blackens in the same manner, so that it is impossible to save the plant except by cutting it to the ground. If by means of heat, the effects are nearly similar, as may oftentimes be seen in gardens, or even in forests, where the foresters are allowed to clear away the moss and withered leaves from the roots. Sometimes the disease is occasioned by the too rapid growth of a particular branch, depriving the one that is next it of its due nourishment, and hence inducing its decay. Sometimes it is occasioned by means of parasitical plants, as in the case of the bulbs of the saffron, which a species of lycoperdon often attaches itself to and totally

corrupts.

1670. Dry gangrene. The harmattan winds of the coast of Africa kill many plants, by means of inducing a sort of gangrene that withers and blackens the leaves, and finally destroys the whole plant. The nopal of Mexico is also subject to a sort of gangrene that begins with a black spot, and extends till the whole leaf or branch rots off, or the plant dies. But plants are sometimes affected with a gangrene by which a part becomes first soft and moist, and then dissolves into foul ichor. This is contined chiefly to the leaves, flowers, and fruit. Sometimes it attacks the roots also, but rarely the stem. It seems to be owing, in many cases, to too wet or too rich a soil; but it may originate in contusion, and may be caught by infection. But the nopal is subject also to a disease called by Thiery, la dissolution, considered by Sir J. E. Smith as distinct from gangrene, and which appears to be Willdenow's dry gangrene. A joint of the nopal, or a whole branch, and sometimes an entire plant, changes in the space of a single honar, from a state of apparent health to a state of putrefaction or dissolution. Now its surface is verdant and shining, and in an instant it changes to a yellow, and its brilliancy is gone. If the substance is cut Lato, the parts are found to have lost all cohesion, and are quite rotten; the attempt at a cure is by speedy amputation below the diseased part. Sometimes the vital principle collecting and exerting all its energies, raakes a stand as it were against the encroaching disease, and throws off the infected part. (Smith's Introduction, p. 340.)

1671. Etiolation. Plants are sometimes affected by a disease which entirely destroys their verdure, and renders them pale and sickly. This is called ctiolation, and may arise merely from want of the agency of light, by which the extrication of oxygen is effected, and the leaf rendered green. And hence it is that plants placed in dark rooms, or between great masses of stone, or in the clefts of rocks, or under the shade of other trees,

look always peculiarly pale. But if they are removed from such situations, and exposed to the action of light, they will again recover their green color. Etiolation may also ensue from the depredation of insects nestling in the radicle, and consuming the food of the plant, and thus debilitating the vessels of the leaf so as to render them insusceptible of the action of light. This is said to be often the case with the radicles of secale cereale; and the same result may also arise from poverty of soil.

1672. Suffocation. Sometimes it happens that the pores of the epidermis are closed up, and transpiration consequently obstructed, by means of some extraneous substance that attaches itself to and covers the bark. This obstruction induces disease, and the disease is called suffocation.

1673. Sometimes it is occasioned by the immoderate growth of lichens upon the bark covering the whole of the plant, as may be often seen in fruit-trees, which it is necessary to keep clean by means of scraping off the lichens, at least from the smaller branches. For if the young branches are thus coated, so as that the bark cannot perform its proper functions, the tree will soon begin to languish, and will finally become covered with fungi, inducing or resulting from decay, till it is at last wholly choked up.

1674. But a similar effect is also occasionally produced by insects, in feeding upon the sap or shoot. This may be exemplified in the case of the aphides, which sometimes breed or settle upon the tender shoot in such multitudes as to cover it from the action of the external air altogether. It may be exemplified also in the case of Coccus Hesperidum and Acarus tellarius, insects that infest hot-house plants, the latter by spinning a fine and delicate web over the leaf, and thus preventing the access of atmospheric air. Insects are to be removed either by the hand or other mechanical means, or destroyed by excess of some of the elements of their nutrition, as heat, or cold, or moisture, where such excess does not prove injurious to the plant; or by a composition either fluid or otherwise, which shall have the same effects. Prevention is to be attempted by general culture, and particular attention to prevent the propagation of the insects or vermin, by destroying their embryo progeny, whether oviparous or otherwise.

1675. Sometimes the disease is occasioned by an extravasation of juices which coagulate on the surface of the stalk so as to form a sort of crust, investing it as a sheath, and preventing its further expansion. 1676. Sometimes the disease is occasioned from want of an adequate supply of nourishment as derived from the soil, in which the lower part of the plant is the best supplied, while the upper part of it is starved. Hence the top shoots decrease in size every succeeding year, because sufficient supply of sap cannot be obtained to give them their proper developement. This is analogous to the phenomena of animal life, when the action of the heart is too feeble to propel the blood through the whole of the system: for then the extremities are always the first to suffer. And perhaps it may account also for the fact, that in bad soils and unfavorable seasons, when the ear of barley is not wholly perfected, yet a few of the lower grains are always completely developed. (Smith's Introduction, p. 344.)

1677. Contortion. The leaves of plants are often injured by means of the puncture of insects, so as to induce a sort of disease that discovers itself in the contortion or convolution of the margin, or wrinkled appearance of the surface. The leaves of the apricot, peach, and nectarine, are extremely liable to be thus affected in the months of June and July.

1678. The leaf that has been punctured soon begins to assume a rough and wrinkled figure, and a reddish and scrofulous appearance, particularly on the upper surface. The margins roll inwards on the under side, and enclose the eggs which are scattered irregularly on the surface, giving it a blackish and granular appearance, but without materially injuring its health. In the vine, the substance deposited on the leaf is whitish, giving the under surface a sort of a frosted appearance, but not occasioning the red and scrofulous aspect of the upper surface of the leaf of the nectarine. In the poplar, the eggs when first deposited resemble a number of small and hoary vesicles containing a sort of clear and colorless fluid. The leaf then becomes reflected and conduplicated, enclosing the eggs, with a few reddish protuberances on the upper surface. The embryo is nourished by this fluid; and the hoariness is converted into a fine cottony down, which for some time envelopes the young fly. The leaf of the lime-tree in particular is liable to attacks from insects when fully expanded; and hence the gnawed appearance it so often exhibits. The injury seems to be occasioned by some species of puceron depositing its eggs in the parenchyma, generally about the angles that branch off from the midrib. A sort of down is produced, at first green, and afterwards hoary; sometimes in patches, and sometimes pervading the whole leaf; as in the case of the vine. Under this covering the egg is hatched; and then the young insect gnaws and injures the leaf, leaving a hole, or scar of a burnt or singed appearance. Sometimes the upper surface of the leaf is covered with clusters of wart-like substances somewhat subulate and acute. They seem to be occasioned by means of a puncture made on the under surface, on which a number of openings are discoverable, penetrating into the warts, which are hollow and villous within. The disease admits of palliation by watering frequently over the leaves; and by removing such as are the most contorted and covered by larvæ.

1679. Consumption. From barren or improper soil, unfavorable climes, careless planting, or too frequent flowering exhausting the strength of the plant, it often happens that disease is induced which terminates in a gradual decline and wasting away of the plant, till at length it is wholly dried up. Sometimes it is also occasioned by excessive drought, or by dust lodging on the leaves, or by fumes issuing from manufactories which may happen to be situated in the neighborhood, or by the attacks of insects.

1680. There is a consumptive affection that frequently attacks the pine-tree, called Teredo Pinorum (Wildenow, Princ. Bot. p. 351.), which affects the alburnum and inner bark chiefly, and seems to proceed from long continued drought, or from frost suddenly succeeding mild or warm weather, or heavy winds. The leaves assume a tinge of yellow, bordering upon red. A great number of small drops of resin exude from the middle of the boughs, of a putrid odor. The bark exfoliates, and the alburnum presents a livid appearance. The tree swarms with insects, and the disease is incurable, inducing inevitably the total decay and death of the individual. The preventive is obviously good culture, so as to maintain vigorous health palliatives may be employed according to the apparent cause of the disease.

SECT. III. Natural Decay.

1681. Although a plant should not suffer from the influence of accidental injury, or from disease, still there will come a time when its several organs will begin to experience the approaches of a natural decline insensibly stealing upon it, and at last inducing death. The duration of vegetable existence is very different in different species. Yet in the vegetable, as well as in the animal kingdom, there is a term or limit set, beyond which

the individual cannot pass. Some plants are annuals and last for one season only, springing up suddenly from seed, attaining rapidly to maturity, producing and again sowing their seeds, and afterwards immediately perishing. Such is the character of the various species of corn, as exemplified in oats, wheat, and barley. Some plants continue to live for a period of two years, and are therefore called biennials, springing up the first year from seed, and producing roots and leaves, but no fruit; and in the second year producing both flower and fruit, as exemplified in the carrot, parsnep, and caraway. Other plants are perennials, that is, lasting for many years; of which some are called under-shrubs, and die down to the root every year; others are called shrubs, and are permanent both by the root and stem, but do not attain to a great height or great age; others are called trees, and are not only permanent by both root and stem, but attain to a great size, and live to a great age. But even of plants that are woody and perennial, there are parts which perish annually, or which are at least annually separated from the individual; namely, the leaves, flowers, and fruit, leaving nothing behind but the bare caudex, which submits in its turn to the ravages of time, and ultimately to death.

1682. The decay of the temporary organs, which takes place annually, is a phenomenon familiar to every body, and comprehends the fall of the leaf, the fall of the flower, and the fall of the fruit.

1685. The fall of the leaf, or annual defoliation of the plant, commences for the most part with the colds of autumn, and is accelerated by the frosts of winter, that strip the forest of its foliage, and the landscape of its verdure. But there are some trees that retain their leaves throughout the whole of the winter, though changed to a dull and dusky brown, and may be called ever-clothed trees, as the beech: and there are others that retain their verdure throughout the year, and are denominated evergreens, as the holly. The leaves of both sorts ultimately fall in the spring. Sir J. E. Smith considers that leaves are thrown off by a process similar to that of the sloughing of diseased parts in the animal economy; and Keith observes, that if it is necessary to illustrate the fall of the leaf by any analogous process in the animal economy, it may be compared to that of the shedding of the antlers of the stag, or of the hair or feathers of other beasts or birds, which being, like the leaves of plants, distinct and peculiar organs, fall off, and are regenerated annually, but do not slough.

1684. The flowers, which, like the leaves, are only temporary organs, are for the most part very shortlived; for as the object of their production is merely that of effecting the impregnation of the germs, that object is no sooner obtained than they begin again to give indications of decay, and speedily fall from the plant; so that the most beautiful part of the vegetable is also the most transient.

165. The fruit, which begins to appear conspicuous when the flower falls, expands and increases in volume, and, assuming a peculiar hue as it ripens, ultimately detaches itself from the parent plant, and drops into the soil. But it does not in all cases detach itself in the same manner: thus, in the bean and pea the seed-vessel opens and lets the seeds fall out, while in the apple, pear, and cherry, the fruit falls entire, enclosing the seed, which escapes when the pericarp decays. Most fruits fall soon after ripening, as the cherry and apricot, if not gathered; but some remain long attached to the parent plant after being fully ripe, as in the case of the fruit of euonymus, and mespilus. But these, though tenacious of their hold, detach themselves at last, as well as all others, and bury themselves in the soil, about to give birth to a new individual in the germination of the seed. The fall of the flower and fruit is accounted for in the same manner as that of the leaf. Such then is the process and presumptive raBut there is

1686. Decay of the permanent organs. tionale of the decay and detachment of the temporary organs of the plant. also a period beyond which even the permanent organs themselves can no longer carry on the process of vegetation. Plants are affected by the infirmities of old age as well as animals, and are found to exhibit also similar symptoms of approaching dissolution. The root refuses to imbibe the nourishment afforded by the soil, or if it does imbibe a portion, it is but feebly propelled, and partially distributed, through the tubes of the alburnum; the elaboration of the sap is now effected with difficulty as well as the assimilation of the proper juice, the descent of which is almost totally obstructed; the bark becomes thick and woody, and covered with moss or lichens; the shoot becomes stunted and diminutive; and the fruits palpably degenerate, both in quantity and quality. The smaller or terminal branches fade and decay the first, and then the larger branches also, together with the trunk and root; the vital principle gradually declines without any chance of recovery, and is at last totally extinguished." When life is extinguished, nature hastens the decomposition; the surface of the tree is overrun with lichens and mosses, which attract and retain the moisture; the empty pores imbibe it, and putrefaction speedily follows. Then come the tribes of fungi, which florish on decaying wood, and accelerate its corruption; beetles and caterpillars take up their abode under the bark, and bore innumerable holes in the timber; and woodpeckers in search of insects pierce it more deeply, and excavate large hollows, in which they place their nests. Frost, rain, and heat assist, and the whole mass crumbles away, and dissolves into a rich mould." (Dial. on Bot. p. 365.)

CHAP. VI.

Vegetable Geography and History, or the Distribution of Vegetables relatively to the Earth

and to Man.

1687. The science of the distribution of plants, Humboldt observes (Essai sur la Geographie des Plantes, &c. 1807), considers vegetables in relation to their local associations in

different climates. It points out the grand features of the immense extent which plants occupy, from the regions of perpetual snow to the bottom of the ocean, and to the interior of the globe, where, in obscure grottoes, cryptogamous plants vegetate, as unknown as the insects which they nourish. The superior limits of vegetation are known, but not the inferior; for every where in the bowels of the earth are germs which develope themselves when they find a space and nourishment suitable for vegetation. On taking a general view of the disposition of vegetables on the surface of the globe, independently of the influence of man, that disposition appears to be determined by two sorts of causes, geographical and physical. The influence of man, or of cultivation, has introduced a third cause, which may be called civil. The different aspects of plants, in different regions, has given rise to what may be called their characteristic or picturesque distribution; and the subject of distribution may be also considered relatively to the systematic divisions of vegetables, their arithmetical proportions, and economical applications.

SECT. I. Geographical Distribution of Vegetables.

1688. The territorial limits to vegetation are determined in general by three different causes. By sandy deserts, which seeds cannot pass over either by means of winds or birds, as that of Sahara, in Africa; 2. By seas too vast for the seeds of plants to be drifted from one shore to the other, as in the ocean; while the Mediterranean sea, on the contrary, exhibits the same vegetation on both shores; and, 3. By long and lofty chains of mountains. To these causes are to be attributed the fact, that similar climates and soils do not always produce similar plants. Thus in certain parts of North America, which altogether resemble Europe in respect to soil, climate, and elevation, not a single European plant is to be found. The same remark will apply to New Holland, the Cape of Good Hope, Senegal, and other countries, as compared with countries in similar physical circumstances, but geographically different. The separation of Africa and South America, Humboldt considers, must have taken place before the developement of organised beings, since scarcely a single plant of the one country is to be found in a wild state in the other.

SECT. II. Physical Distribution of Vegetables.

1689. The natural circumstances affecting the distribution of plants, may be considered in respect to temperature, clevation, moisture, soil, and light.

1690. Temperature has the most obvious influence on vegetation. Every one knows that the plants of hot countries cannot in general live in such as are cold, and the contrary. The wheat and barley of Europe will not grow within the tropics; the same remark applies to plants of still higher latitudes, such as those within the polar circles, which cannot be made to vegetate in more southern latitudes; nor can the plants of more southern latitudes be made to vegetate there. In this respect, not only the medium temperature of a country ought to be studied, but the temperature of different seasons, and especially of winter. Countries where it never freezes; those where it never freezes so strong as to stagnate the sap in the stems of plants; and those where it freezes sufficiently strong to penetrate into the cellular tissue; form three classes of regions in which vegetation ought to differ. But this difference is somewhat modified by the effect of vegetable structure, which resists, in different degrees, the action of frost; thus, in general, trees which lose their leaves during winter resist the cold better than such as retain them; resinous trees more easily than such as are not so; herbs of which the shoots are annual and the root perennial, better than those where the stems and leaves are persisting; annuals which flower early, and whose seeds drop and germinate before winter, resist cold less easily than such as flower late, and whose seeds lie dormant in the soil till spring. Monocotyledonous trees, which have generally persisting leaves and a trunk without bark, as in palms, are less adapted to resist cold than dicotyledonous trees, which are more favorably organised for this purpose, not only by the nature of their proper juice, but by the disposition of the cortical and alburnous layers, and the habitual carbonisation of the outer bark. Plants of a dry nature resist cold better than such as are watery; all plants resist cold better in dry winters than in moist winters; and an attack of frost always does most injury in a moist country, in a humid season, or when the plant is too copiously supplied with

water.

1691. Some plants of firm texture, but natives of warm climates, will endure a frost of a few hours' continuance, as the orange at Genoa, (Humboldt, De Distributione Plantarum); and the same thing is said of the palm and pine-apple, facts most important for the gardener. Plants of delicate texture, and natives of warm climates, are destroyed by the slightest attack of frost, as the phaseolus, nasturtium, &c.

1692. The temperature of spring has a material influence on the life of vegetables; the injurious effects of late frosts are known to every cultivator. In general, vegetation is favored in cold countries by exposing plants to the direct influence of the sun; but this excitement is injurious in a country subject to frosts late in the season; in such cases, it is better to retard than to accelerate vegetation.