the hairs are then said to be plumose. It sometimes happens that little branchlets are produced on one side only of a hair, as on the leaves of Siegesbeckia orientalis, in which case the hair is called one-sided (secundatus); very rarely they appear upon the articulations of the hair, which in that case is called ganglioneous. (Plate I. fig. 9. Verbascum Lychnitis): the poils en goupillon of De Candolle are referable to this form. Besides these, there are many other modifications. Hairs are conical, cylindrical, or moniliform, thickened slightly at the articulations (torulose), as in Lamium album, or much enlarged at the same point (nodulose), as in the calyx of Achyranthes lappacea.

Hairs are sometimes said to be fixed by their middle (Plate I. fig. 10. c); a remarkable structure, common to many different genera; as Capsella, Malpighia, Indigofera, &c. This expression, however, like many others commonly used in botany, conveys a false idea of the real structure of such hairs. They are in reality formed by an elevation of one cellule of the cuticle above the level of the rest, and by the developement of a simple hair from its two opposite sides. Such would be more correctly named divaricating hairs. When the central cellule has an unusual size, as in Malpighia, these hairs are called poils en navette (pili Malpighiacei) by M. De Candolle; and when the central cellule is not very apparent, poils en fausse navette (pili pseudo-Malpighiacei, biacuminati), as in Indigofera, Astragalus, Asper, &c. In many plants the hairs grow in clusters, as in Malvaceæ, and are occasionally united at their base: such are called stellate, and are frequently peculiar to certain natural orders. (Plate I. fig. 10. a.)

All these varieties belong to one or other of the two principal kinds of hairs; viz. the Lymphatic and the. Secreting. Of these, lymphatic hairs consist of tissue tapering gradually from the base to the apex; and secreting, of cellules visibly distended either at the apex or base into receptacles of fluid. Malpighiaceous and glandular hairs, stings, and those which cause asperity on the surface of any thing, belong to the latter; almost all the other varieties to the former.

When hairs arise from one surface only of any of the

appendages of the axis, it is almost always from the under surface; but the seed leaves of the nettle, and the common leaves of Passerina hirsuta, are mentioned by M. De Candolle as exceptions to this rule: certain states of Rosa canina might also be mentioned as exhibiting a similar phenomenon. When a portion only of the surface of any thing is covered by hairs, that portion is uniformly the ribs or veins. According to M. De Candolle, hairs are not found either upon true roots, except at the moment of germination, nor upon any part of the stem that is formed under ground, nor upon any parts that grow under water.

4. Of Scales.

SCALES are thin flat membranous processes, formed of cellular tissue springing from the cuticle. They may be considered as hairs of a higher order, - as organs of the same nature, but more developed; for they differ from hairs only in their degree of composition. They are of two kinds, Scales properly so called, and Ramenta. Care must be taken not to confound scales of this description with scales of the stem, to be described hereafter: those now under consideration being mere processes of the cuticle; those to be noticed hereafter being peculiar modifications of leaves.

Scales, properly so called, are the small, roundish, flattened particles which give a leprous appearance to the surface of certain plants, as the Elæagnus and the Ananassa. (Plate I. fig. 10. b.) They consist of a thin transparent membrane, attached by its middle, and, owing to the imperfect union towards its circumference, of the cellular tissue of which it is composed, having a lacerated irregular margin. A scale of this nature is called in Latin composition lepis, and a surface covered by such scales lepidotus, and not squamosus, which is only applied to a surface covered with the rudiments of leaves. Scales are the poils en écusson (pili scutati) of De Candolle.

Ramenta (Vaginella) are thin, brown, foliaceous scales, appearing sometimes in great abundance upon young shoots. They are particularly numerous, and highly developed, upon the petioles and the backs of the leaves of Ferns. They consist of cellular tissue alone, without any vascular

bundles, and are known from leaves not only by their anatomical structure, but also by their irregular position, and by the absence of buds from their axillæ. The student must particularly remark this, or he will confound with them leaves having a ramentaceous appearance, such as are produced upon the young shoots of Pinus. Link remarks, that they are very similar in structure to the leaves of mosses. The term striga has occasionally been applied to them (Dec. Théor. Elém. ed. 2. 376. Link, Elem, 240.); but that word was employed by Linnæus to designate any stiff bristle-like process, as the spines of the Cactus, the divaricating hairs of Malpighia, and the stiff stellated hairs of Hibiscus. So vague an application of the term is very properly avoided at the present day, and the substantive is rejected from modern glossology; the adjective term strigose is, however, occasionally still employed to express a surface covered with stiff hairs.

5. Of Glands.

GLANDS are elevated spaces in the stratum of parenchyma lying immediately below the cuticle, in which they cause projections. They are of several kinds.

Stalked glands are elevated on a stalk which is either simple or branched: they secrete some peculiar matter at their extremities, and are often confounded with the glandular hairs above described, from which they have been well distinguished by Link. According to that botanist, they are either simple or compound; the former consisting of a single cell, and placed upon a hair acting as a simple conduit, occasionally interrupted by divisions; the latter consisting of several cells, and seated upon a stalk containing several conduits, formed by rows of cellular tissue. They are common upon the rose and the bramble, in which they become very rigid, and assume the nature of aculei. For the sake of distinguishing them from the latter, they have been called setæ by Woods and myself, but improperly; they are also the aiguillons of the French. In Hypericum they abound on the calyx and corolla of some species, but do not give out any exudation; they contain, however, a deep red juice within

their cells. In some Jatrophas they are much branched; in many Diosmeæ they form a curious humid appendage at the apex of the stamens.

Sessile glands are produced upon various parts, and are extremely variable in figure. In Cassias, they are seated upon the upper edge of the petiole, and are usually cylindrical or conical; in Cruciferous plants they are little roundish shining bodies, arising from just below the base of the ovarium; in the leafless Acacias, they are a little depressed, with a thickened rim, and placed on the upper edge of the phyllodium; they are little kidney-shaped bodies upon the petiole of the Peach and other drupaceous plants; and they assume many more appearances.

Verruca, or warts, are roundish excrescences, formed of cellular tissue filled with opaque matter, and are situated upon various parts. They are common upon the surface of the leaves of the Aloe, where they are very large; upon the stem, as in Euonymus verrucosus; upon the petiole, as in Passiflora; they are also found upon the calyx, as in some species of Campanula, and at the serratures of the leaves, when they are considered by M. Röper (De Floribus Balsaminearum, p. 15.) to be abortive ovula. They also appear upon the pericarpium and the testa of the seed; in the latter case they are called spongiola seminales by De Candolle. They are round, oblong, or reniform, and occasionally cupulate, when they receive the name of glandes à godet (glandulæ urceolares) from some French writers. Verrucæ are the glandes cellulaires of Mirbel; but they must not be confounded with the glandes vasculaires of the same writer, which are not mere excrescences of the epidermis, but modifications of well known organs. (See Discus, further on.) The presence of minute verrucæ upon the surface of a leaf gives rise to a peculiar kind of roughness which is called scabrities, and such a surface is then said to be scabrous (scaber): this must not be confounded with asperity.

Papilla (Glandulæ utriculaires of Guettard) are minute transparent elevated points of the cuticle, filled with fluid, and covering closely the whole surface upon which they appear. In other words, they are elevated, distended cellules of the

cuticle. The presence of papillæ upon the leaves of the ice plant gives rise to the peculiar crystalline nature of its surface; they also cause the satiny appearance of the petals, upon which they almost always exist in great quantities. Link remarks, that the petals of Plantago, which are destitute of papillæ, are also without the usual satiny lustre of those organs. When the papillæ are much elongated beyond the surface, as in many stigmas, of which they form the collecting fringes, they receive sometimes the name of papulæ. It should be observed, that in M. De Candolle's Théorie Elémentaire, these two terms are transposed, each having received the definition belonging to the other.

Lenticular glands (Lenticelles of De Candolle; Glandes lenticulaires of Guettard ;) are brown oval spots found upon the bark of many plants, especially willows: they indicate the points from which roots will appear if the branch be placed in circumstances favourable to their production. They are considered by M. De Candolle to bear the same relation to the roots that buds bear to young branches. (De Candolle, Premier Mém. sur les Lentic., in the Ann. des Sciences Naturelles.)

6. Of Prickles.

PRICKLES (aculei) are rigid, opaque, conical processes, formed of masses of cellular tissue, and terminating in an acute point. They may be, not improperly, considered as very compound indurated hairs. They have no connection with the woody fibre, by which character they are obviously distinguished from spines, of which mention will be made under the head of branches, of which spines are an abortion. Prickles are found upon all parts of a plant, except the stipulæ and stamens. They are very rarely found upon the corolla, as in Solanum Hystrix; their most usual place is upon the stem, as in Rosa, Rubus, &c.

SECT. II. Of the Stem or Ascending Axis.

WHEN a plant first begins to grow from the seed, it is a little body called an embryo, with two opposite extremities, of