ADHESION, in Botany, is applied to the union of parts which are separate in other plants, or in younger states of the same plant. Many of the characters which cause the diversity of appearance in the vegetable kingdom originate in the adhesion of n few very simple organs ; and what we are accustomed to consider parts of extremely different nature, only seem so in consequence of the way in which such adhesion occurs. Thus, the stem of a tree is not a homogeneous masa of vegetable matter, perforated by holes, or filled by little cavities caused by the extrication of air in it when in a soft state, but is produced by the adhesion of certain elementary bellies, called Cellular Tissue and Vascular Tissue [Tessera, Verrerstme), arranged in a definite manner, which varies in every species; neither is n leaf, or a fruit, or a flower, a mere niters of pulp, or an expansion, like the horn of an animal, but also consists of those same elementary organs in a state of adhesion.
Guided by these facts, modern botanists have made use of this property of adhesion to explain the nature of every organ that plants bear, and there are few anomalies that are not due in a great measure to the union of contiguous Parts.
Some leaves are said to be stem-clasping, or amplexicaul, when their base partially surrounds the stem (fig. a); while some stems are said to be perfoliate, when they seem as if they pierced through the leaf; as in Buplettrunt rotundifolium (fig. b); but the latter differ from the former only in this, that in the first the lobes at the base of the leaf embrace the stem without adhering, while in the second they not only clasp the stem but grow together where their margins come in contact. Some leaves are hollow, as in the Pitcher Plant, and these were formerly thought to be special organs with which no analogy could be discovered ; they are now known to be leaves which have rolled up so that their opposite margins come in contact and adhere. Other leaves, growing from opposite sides of a stem, adhere in conse quence of their bases becoming connate (fig. c), as in the honeysuckle ; and finally there are others, many of which grow in what botanists call a whorl, that is to say, all round a stem upon the same plane, and adhere by their margins into a sheath (fig. d), as in Casuarina.
In other organs adhesions of a similar nature occur.
In the calyx, all the sepals, or parts, are often distinct, as in the Ranunculus; but they also often adhere by their edges, into a sort of cup, as in the cherry. In the corolla the petals are either all separate, as in the rose, or they adhere by their edges into a cup or bell, as in the different heaths, Campanula, and the like.
Similar adhesions take place between the stamens. In the rose they are all distinct from each other ; in the geranium they slightly adhere at the base (fig. e); in the mallow they adhere into a tube, except near the upper extremity, where they are not united, and have their ordinary appearance (fig. f ); in other plants they grow together into a solid tube in which no trace of separation can bo discovered, as in the genus Cuarea (fig. g).
Finally, in the pistil there are certain parts called carpels, each of which is a hollow body terminated by a style and stigma. These carpels are hollow, because they are formed of a flat organ, doubled up so that its edges come in contact and adhere to each other. Sometimes only one carpel is present in a flower, as in the cherry (fig. It); sometimes several, as in the rose (fig. i). In the Nigella, the styles of the carpels are all distinct (fig. k), but in the lily and the myrtle (fig. I) the styles of the carpels adhere so completely that there seems to be but one. In the apple, the calyx seems to grow from the top of the fruit ; this is caused by the carpels having at a very early period adhered to the inside of the calyx, which afterwards grows with their growth, and, finally, leaves its extremities in a withered state near the top of the carpels : in the cherry, on the contrary, no adhesion ever takes place between the carpel and the calyx ; and, consequently, when the fruit is ripe, there is no trace of the latter upon its upper end. In the raspberry, the fruit is enabled to slip like a thimble from off the receptacle, because the carpels all adhere by their sides.
( De Candolle, Thu Orie Elementaire de la Botanigue ; Lindley, Intro duction to Botany ; Schleiden, Principles of Scientific Botany.)