(from de, and folium, a leaf), the fall of the leaves; a term opposed to frondescens, the annual renovation of the leaves, produced by the unfolding of the buds in spring.

Most plants in cold and temperate climates shed their leaves every year. This happens in autumn, and is generally announced by the flowering of the common meadow saffron. The term is only applied to trees and shrubs; for herbs perish down to the roots every year, losing stem, leaves, and all. All plants do not drop their leaves at the same time. Amongst large trees, the ash and walnut, although the latest in unfolding, are soonest divested of their leaves; which, indeed, the latter seldom carries above five months. On the oak and hornbeam the leaves die and wither as soon as the cold commences; but they remain attached to the branches until they are pushed off by the new ones, which unfold themselves the following spring. These trees are doubtless a kind of evergreens. The leaves are probably destroyed only by cold; and perhaps would continue longer on the plant, but for the force of the spring sap joined to the moisture.

In mild and dry seasons the lilac, privet, yellow jessamine of the woods, and maple of Crete, preserve their leaves green until spring, and do not drop them till the new leaves are beginning to appear. The fig-tree, and many other trees that grow between the tropics, are of this particular class of evergreens. The trees in Egypt, as Hasselquist observes, cast their leaves in the latter end of December and beginning of January, having young leaves ready before all the old ones have fallen off; and, to forward this operation of nature, few of the trees have buds; the sycamore and willow, indeed, have some, but with few and quite loose ti-

pules or scales. Buds seem to be less necessary in southern Deformity than in northern countries.

Lastly, some trees and shrubs preserve their leaves throughout the year, and are not in the least influenced by the clemency or inclemency of seasons. Such are the firs, juniper, yew, cedar, cypress, and many other trees; hence denominated "evergreens." These preserve their old leaves long after the formation of the new, and do not drop them at any determinate time. In general the leaves of evergreens are harder and less succulent than those which are renewed annually. The trees are generally natives of warm climates, as the alaternus or rhampus of France and Italy, and the evergreen oak of Spain, Portugal, and Sardinia.

Some herbaceous perennials, as the house-leeks and navel-worts, enjoy the same privilege with the evergreen trees, and resist the severities of winter; some even can dispense with the earth for a time, being replete with juices, which the leaves imbibe from the humidity of the atmosphere, and which in such plants are of themselves sufficient for effecting the purposes of vegetation. It is for this reason that, unless in excessively hot weather, gardeners seldom water succulent plants, as the aloes, which rot when they are moistened, if the sun does not quickly dry them.

The leaves of all the evergreen shrubs and trees have a thin compact skin or cover over their surface, as is easily discovered by macerating them in water, in order to separate the parenchyma or pulp from the vessels of the leaves, which cannot be effected in any of these evergreens till a thin parchment-like cover is taken off. These trees and shrubs are found by experiment to perspire but little, when compared with others which shed their leaves; and it is, perhaps, principally owing to this close covering, as also to the small proportion of moisture contained in their vessels, that they retain their verdure, and continue through the winter on the trees. The nutritive juices of these plants always abound more or less with an oily quality, which secures them from being injured by severe frosts; so that many of these evergreen trees are adapted to grow in the coldest parts of the habitable world.

With respect to deciduous trees, the falling off of the leaves seems principally to depend on the temperature of the atmosphere, which likewise serves to hasten or retard the process in question. A hot sun contributes to hasten the dropping of the leaves; and hence in warm and very dry summers the leaves of the lime-tree and horse-chestnut turn yellow about the first of September, whilst in ordinary years the yellowness does not appear till the beginning of October. Nothing, however, contributes more to hasten the fall of the leaves than immoderate cold or moist weather in autumn; but moderate droughts serve to retard it. As a proof of this position, M. Adanson relates, that in the year 1759, the leaves of the elm-tree, which generally fall off about the 25th of November, continued in verdure and vigour at Paris, where the autumn was remarkably dry, till the tenth of the following month.

It deserves to be remarked, that an evergreen grafted upon a deciduous tree determines the latter to retain its leaves. This observation is confirmed by repeated experiments, particularly by grafting the laurel, or cherry-bay, an evergreen, on the common cherry; and the ilex, or evergreen oak, on the oak.