green body, occupying the place and performing the functions of a leaf, and closed at its extremity by a lid, termed the operculum. The pitcher, or fistular part, is the petiole, and the operculum the blade of a leaf in an extraordinary state of transformation. This is found, by a comparison of Nepenthes and Sarracenia with Dionæa muscipula; in that plant the leaf consists of a broad-winged petiole, articulated with a collapsing blade, the margins of which are pectinate and inflexed. If we suppose the broad-winged petiole to collapse, and that its margins, when they meet, cohere, there would then be formed a fistular body like the pitcher of Sarracenia (fig. 58. B), and there would be no difficulty in identifying the acknowledged blade of the one with the operculum of the other. From Sarracenia the transition to Nepenthes (fig. 58. A) is obvious.

So.

The student must not, however, suppose that all pitchers are petioles, because those of Nepenthes and Sarracenia are Those of the curious Dischidia Rafflesiana (fig. 59.), figured by Wallich in his Planta Asiatica Rariores, are leaves, the margins of which are united. The pitchers of Marcgraavia and Norantea (fig. 60.) are bracts in the same state.

Spines of the leaves are formed either by a lengthening of the woody tissue of the veins, or by a contraction of the

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parenchyma of the leaves: in the former case they project beyond the surface or margin of the leaf, as in many Solana and the Holly (Ilex aquifolium): in the latter they are the veins themselves become hardened, as in the palmated spines of the Barberry; the spiny petiole of many Leguminous plants is of the same nature as the latter. So strong is the tendency in some plants to assume a spiny state, that in a species of Prosopis from Chili, of which I have a living specimen now before me, half the leaflets of its bipinnate leaves have the upper half converted into spines.

2. Of Stipules.

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At the base of the petiole, on each side, is frequently seated a small appendage, most commonly of a texture less firm than the petiole, and having a tapering termination. These two appendages are called stipules. They either adhere to the base of the petiole or are separate; - they either endure as long as the leaf, or fall off before it; they are membranous, leathery, or spiny; - finally, they are entire or laciniated.

By Link they have been called Paraphyllia, and defined as “foliaceous parts, in structure like the leaves, and developed before those organs."

When they are membranous, and surround the stem like a sheath, cohering by their anterior margins, as in Polygonum (fig. 61. a), they have been termed ochrea by Willdenow. Of this the fibrous sheath at the base of the leaves of Palms, called reticulum by some, may possibly be a modification. In pinnated leaves there is often a pair of stipules at the base of each leaflet, as well as two at the base of the common petiole : stipules, under such circumstances, are called stipels.

What stipules really are is not well made out. De Candolle seems, from some expressions in his Organographie, to suspect their analogy with leaves; while, in other places in the same work, it may be collected that he rather considers them special organs. I am clearly of opinion that, notwithstanding the difference in their appearance, they are really accessory leaves: first, because they are occasionally transformed, in Rosa bracteata, into pinnated leaves; secondly, because they are often undistinguishable from leaves, of which they obviously perform all the functions, as in Lathyrus, Lotus, and many other Fabaceæ: and, finally, because there are cases in which buds develope in their axils, as in Salix, a property peculiar to leaves and their modifications. De Candolle, in suggesting, after Seringe, that the tendrils of Cucurbitaceae are modified stipules, assigns the latter a tendency to a transformation exclusively confined either to the midrib of a leaf, or to a branch; and they cannot be the latter. It is, however, more probable that the tendril in this order is an accessory bud, a little out of its place, as the Bravais' have suggested. (Ann. Sc., n. s., VIII. 20.)

It is sometimes difficult to distinguish from true stipules certain membranous expansions, or ciliæ, or glandular appendages of the margin of the base of the petiole, such as are found in Ranunculaceæ, Apocynaceæ, Apiacea, and many other plants. In these cases the real nature of the parts is only to be collected from analogy, and by comparing them with the same part differently modified in neighbouring species.

Link regards the scales of leafbuds (called by him tegmenta) as a kind of stipule, and such they, no doubt, sometimes are, as in Liriodendron; but then he unites with them the primordial ramentaceous leaves of Pinus, which have no analogy with stipules.

De Candolle remarks, that no Monocotyledonous plants have stipules; but they certainly exist, at least in Naiadacea and Araceæ. It is also said that they do not occur in the embryo; but then there are some exceptions to this statement, as well as to Miquel's remark, that they never occur upon radical leaves, e. g. Strawberry.

Turpin considers them of two kinds.

1. Distinct, but rudimentary, leaves, when they originate from the stem itself, as in Cinchonaceæ, &c.

2. Leaflets of a pinnated leaf, when they adhere to the leafstalk, as in Roses, &c.

The ligula of grasses, at the apex of their sheathing petiole, a membranous appendage, which some have considered stipulary, should rather be considered an expansion analogous to the corona of some Silenaceous plants.

It has been already noted, that when stipules surround the stem of a plant they become an ochrea; in this case their anterior and posterior margins are united by cohesion; a property which they possess in common with all modifications. of leaves, and of which different instances may be pointed out in Magnoliacea, where the back margins only cohere, in certain Cinchonacea, in which the anterior margins of the stipules of opposite leaves are united, and in many other plants.

All the parts hitherto made the subject of inquiry are called organs of vegetation; their duty being exclusively to perform the nutritive parts of the vegetable economy. Those which are about to be mentioned are called organs of fructification; their office being to reproduce the species by a process in some respects analogous to that which takes place in the animal kingdom. The latter are, however, all modifications of the former, as will hereafter be seen, and as the subject of this division is in itself a kind of proof; bracts not being exactly either organs of vegetation or reproduction, but between the two.

Botanists call Bracts either the leaf from the axil of which a flower is developed, such as we find in Veronica agrestis; or else all those leaves which are found upon the inflorescence, and are situated between the true leaves and the calyx. There are, in reality, no exact limits between bracts and common leaves; but in general the former may be known by their situation immediately below the calyx, by their smaller size, difference of outline, colour, and other marks. They are often entire, however much the leaves may be divided; frequently scariose, either wholly or in part; sometimes deciduous before the flowers expand; but rarely very much dilated, as in Origanum Dictamnus, and a few other plants. It is often more difficult to distinguish bracts from the sepals of a polyphyllous calyx than even from the leaves