VARIETY, in botany, a plant changed by some accidental cause, which being removed, the variety or mutation disappears, and the species is restored. As many plants of different form and appearance as are produced from seed of the same species, are to be regarded as genuine varieties, and in all cases to be di-
stinguished with great accuracy from the species.
In the form and disposition of the parts of each individual of the same species, there exists, in general, a constant uniformity. Different causes, however, as culture, climate, exposure, age, diseases, luxuriance or poverty of nourishment, contusions, and other circumstances, produce monstrous appearances and accidental varieties in the parts of plants.
It is known, that a superabundance of nourishment gives rise to the numerous tribe of double and prolific flowers: the same cause gives to all the parts of the plant a thickness and extent by no means natural to them. Hence, likewise, the prodigious multiplication of the leaves of some plants, which increase to such a degree, as frequently to injure the flower and fruit.
The leaves of young trees and of new shoots are much larger, and less cut and ramified, than those of a grown tree of the same species. In holly, the leaves lose their prickles when the tree waxes old.
The lower leaves of aquatic plants, as crow-foot and water-drop-wort, are frequently finely cut like hairs, whilst those above are of a different form. Plants of the same species that grow in another soil have no diversity in the form of their upper and under leaves. Again, in mountainous plants, the lower leaves are generally more entire; the upper ones more divided. Burnet, saxifrage, anise, and coriander, furnish examples.
The seeds or grains of many grasses, particularly of rye, are sometimes prolonged into a horny appearance of a fungous substance, that is pretty hard, and as it were cartilaginous. Some of these monstrous productions are more than two inches long. Rye diseased in this manner, is frequently attended with fatal consequences to such as eat of the bread prepared from it. The same appearance has been observed in gramen aquaticum fuitans, and carex. This disease, termed by Linnæus clavus, is common in moist years and rainy seasons, and seems to be principally owing to a defect of perspiration.
The flowers and seeds of many of the esculent grasses, and some other plants, are frequently reduced into a black powder. This appearance has been particularly observed in wheat, rye, barley, oats, persicaria, marsh-marigold, goats-beard, soap-wort, and some of the lychnis, pink, and chick-weed tribe. In the greater number, the disease, when it attacks the flower, begins by the receptacle under the form of small black points, which insensibly reach the other parts of the flower; as the flower-cup, petals, and stamens, without attacking the pistil or female organ, which however commonly proves abortive.
The disease termed ustilago, or burning, differs from that just mentioned, in that it is contagious and hereditary; the seeds being the only parts that are affected by it. It has been discovered in the same species of grasses as the former, but more abundantly on Indian millet. M. Aymon, a French academician, attributes both these diseases to an internal fault in the sap.
The upper surface of the leaves of some plants, particularly of hop, melon, dead-nettle, hedge-nettle, maple, and gromwell, is subject to be covered with a white appearance, which makes the leaves seem thicker, more weighty, and more opaque. Plants which are attacked by this disease, termed by botanists erysiphe, rarely produce any fruit; or if they do, it is badly formed.
Variety. formed, and has a crude disagreeable taste.
On the under surface of the leaves of ladies' mantle, and a species of euphorbia with cypress leaves, is occasionally dispersed a yellowish dust, which, from its resemblance to rusty iron, has occasioned the name of rubigo, or rust, to be given to this particular disease; which, like the former, appears to proceed from a defect of perspiration.
White spots are frequently observed on some leaves, which thence appear empty, and as it were transparent: it is occasioned by the influence of a burning sun acting upon them when very much moistened, either in consequence of continued rain or a strong dew. When all the leaves are attacked with this disease, which has obtained the name of candor, that is, "the whites," the plant commonly perishes a few days after.
Certain plants of warm climates are subject to lose their petals when cultivated in cold countries; and that even when the fruit arrives at maturity.
Plants which grow in the shade, or in places that are deprived of a proper current of air, are apt to become meagre, and, without taking the consistence which is suitable, to perish before they have produced any fruit. Experiments demonstrate, that the feebleness of such plants proceeds less from a defect of heat, than from a privation of light.
Other causes alter the colour of leaves, and occasionally produce the beautifully variegated leaves so much in request among gardeners. Some leaves are subject to assume a deep red; this is particularly the case with herb Robert, a species of crane's bill.
The branches of ash and willow are frequently flattened in several irregular ways. This is supposed to be in consequence of two buds being naturally grafted in each other before the unfolding of the branch. Two leaves, two fruits, engrafted in this manner, produce other monstrous appearances. By means of artificial grafting, we may in like manner vary the form of leaves, stems, flowers, and fruit.
Lastly, certain insects depositing their eggs under the bark of the leaves and stems of several plants, occasion an extravasation of the sap; and hence give birth to certain singular productions, which in different bodies resemble either nuts, mushrooms, or sponges; and are either round or long, hard or soft, covered with leaves, or guarded with bristly threads.
Such are the galls of oak, which enter into the composition of ink; those of elm, lime, cistus, ground-ivy, a species of hawk-weed, the aspen-tree, and several species of willow. Those of a species of sage, called salvia baccifera, are sold in the markets of the Levant by the name of sage-apples. Tournefort relates that they are round, nine or ten lines in diameter; of the colour of ashes, cottony, with a white pulp that is somewhat transparent, sweet, and of a very agreeable taste. Those of the scarlet-oak are two lines in diameter; the substance is very red, and being dried, is the kermes, or scarlet-pastel, so well known by the dyers.
Of the same nature with the galls just mentioned, are those strange bodies covered with green, red, or yellow fibres, termed bedeguar, which a fly of the same kind produces upon the wild rose: such are likewise the small-bladders on the surface of the elm-leaves, which are filled with gnats, and with an astringent balmy liquor that is an excellent vulnerary.
Such are the principal accidents to which the parts of plants are subject, and which give rise to the numerous tribes of varieties in the vegetable kingdom.