like the rest of their tribe, have the foramen of the ovulum very remote from the placenta, Mons. Adolphe Brongniart has observed, that, at the period of impregnation, the ovula are bent down in such a way as to present their foramina to the conducting tissue; and that when, owing to the shortness of the umbilical cords this is impossible, other not less ingenious means of establishing the contact have been provided by nature.

The function of the stigma has been already shown to be to catch the grains of pollen. This is a mere mechanical operation, and is effected by a viscid secretion, which is generally exuding from the surface of the stigma; which is also generally covered with minute papillæ, or sometimes with fringes, all of which, undoubtedly, aid the action of the organ. In some plants, as in Compositæ, Campanulaceæ, Lobeliaceæ, &c. the style is furnished with a sort of brush, with which it sweeps out the cells of the anthers, and collects the pollen either upon its own stigma, or scatters it upon that which is next it.

CHAPTER VIII.

OF THE FRUIT.

THE fruit, which is mechanically destined as a mere protection to the seed, by which its race is to be maintained, is also, next to the wood, the most important part in the productions of vegetation. It constitutes the principal part of the food, especially in winter, of birds and small animals; it is often more ornamental than the flowers themselves, and it contributes. most materially to the necessities and luxuries of mankind. When ripe, it falls from the plant, and, borne down by its weight, lies on the ground at the foot of the individual that produced it: here its seeds vegetate, when it decays, and a crop of new individuals arises from the base of the old one; but, as plants produced in such a manner would soon choke and destroy each other, nature has provided a multitude of ways for their greater dispersion. Many are carried to distant spots by the animals which eat them; others, provided with a sort of wings, such as the Samara, and the pappus of Compositæ, fly away upon the wind to seek a distant station; others scatter their seeds abroad by an explosion of the pericarpium, caused by a sudden contraction of the tissue; others falling upon the surface of streams, are carried along by the current; while others are dispersed by a variety of methods which it would be tedious to enumerate. The fruit, during its growth, is supported at the expense of the sap generally; but most especially of that which had been previously accumulated for its maintenance. This is less apparent in perennial or ligneous plants than in annual ones, but is capable of demonstration in both. Mr. Knight has well observed, that in annual fruit-bearing plants, such as the melon, if a fruit is allowed to form at a very early period of the life of the plant, as, for instance, in the axilla of the third leaf, it rarely sets or arrives at maturity, but falls off soon after beginning to swell, from want of an accumulation of food for its support; while, if the same

plant is not allowed to bear fruit until it has provided a considerable supply of food, as will be the case after the leaves are fully formed, and have been some little time in action, the fruit which may then set swells rapidly, and speedily arrives at the highest degree of perfection of which it may be susceptible. And in woody trees, also, a similar phenomenon occurs it is well known to gardeners, that, if a season occurs in which trees in a state of maturity are prevented bearing their usual crops, the succeeding year their fruit is unusually fine and abundant; owing to their having a whole year's extra stock of accumulated sap to feed upon.

The cause of the fruit attracting food from surrounding parts is probably to be sought in the phenomenon called endosmose. All the sap that may be at first impelled into the fruit by the action of vegetation, not being able to find an exit, collects within the fruit, and, in consequence of evaporation, becomes gradually more dense than that in the surrounding tissue: it will then begin to attract to itself all the more aqueous fluid that is in communication with it; and the impulse once given in this way to the concentration of the sap in particular points will continue until the growth of the fruit is completed, and its tissue so much gorged as to be incapable of receiving any more food, when it usually falls off.

M. Berard, of Montpelier, has made some curious observations upon the chemical actions of fruit, the substance of which is as follows (See Annales de Chimie, vol. xvi. pp. 152.

Fruit does not act like leaves on the air. The result of its action, as well in light as in darkness, is, at every instant of its formation, a loss of carbon by the fruit, which combines with the oxygen of the air, and forms carbonic acid. This loss of carbon is essential to the ripening of the fruit; for, when the fruit is placed in an atmosphere deprived of oxygen, this function becomes suspended, the ripening is stopped, and, if the fruit remains attached to the tree, it dries up and dies.

A fruit which happens naturally to be enclosed in a shell may, nevertheless, ripen, because the membrane which forms the husk is permeable to the air. The communication between the external and internal air is so free, that the two

portions are always of uniform composition; so that when the air thus contained is analysed, it is always found to be of the same composition as atmospheric air.

When fruits, separated from the tree, but capable of completing their own ripening, are placed in media free from oxygen, they do not ripen: the power, however, is only suspended, and may be re-established by placing the fruit in an atmosphere capable of taking carbon from it. But, if the fruit remain too long in the first situation, although it preserves the same external appearance nearly, it has entirely lost the power of ripening.

Hence it results, that most fruits, and especially those that do not require to remain on the tree, may be preserved for some time, and the pleasure they afford us thus prolonged. The most simple process consists in placing at the bottom of a bottle, a paste formed of lime, sulphate of iron, and water, and afterwards to introduce the fruit, it having been pulled a few days before it would have been ripe. Such fruits are to be kept from the bottom of the bottle, and, as much as possible, from each other; and the bottle to be closed by a cork and cement. The fruits are thus placed in 、an atmosphere free from oxygen, and may be preserved for a longer or shorter time, according to their nature; peaches, prunes, and apricots, from twenty days to a month: pears and apples for three months. If they are withdrawn after this time, and exposed to the air, they ripen extremely well; but, if the times mentioned are much exceeded, they undergo a particular alteration, and will not ripen at all.

Ripe fruit exposed to the air rots and decays: in this case, it first changes the oxygen of the surrounding air into carbonic acid, and then liberates from itself a large quantity of the same acid gas. It appears that the presence of oxygen gas is necessary to the rotting or decay of fruits: when it is absent, a different change takes place.

When the fruit cannot ripen, except on the tree, its ripening is not produced by a chemical change of the substances it contained whilst still green, but by the change of new substances furnished to it by the tree; and when it appears to lose the acid taste it had in its unripe state, it is because that

taste is hidden by the large quantity of sugar it receives in ripening.

In the fruits which ripen off the tree the quantity of sugar is also found considerably to increase; and, in this case, it must be formed at the expense of the substances previously in the fruit. Gum and lignin are the only principles the proportion of which diminish at the same time; it is, therefore, natural to conclude, that it is the portions of these substances which have disappeared that have been converted into sugar; and, as the lignin contains most carbon, it is natural to suppose it is from it the oxygen takes the carbon to form carbonic acid, that change so indispensable to ripening.

Finally, the alteration the lignin suffers in the ripening continues during the decay of the fruit. It becomes brown, and its decomposition occasions the formation of much carbonic acid sugar is also decomposed at this time, and it is to its disappearance that the peculiar taste of decayed fruits is to be attributed. The sugar, in its decomposition, also gives rise, no doubt, to the formation of carbonic acid.