§ 5. The Leaves.
35. The ordinary or perfect Leaf consists of a flat blade or lamina, usually green, and more or less horizontal, attached to the stem by a stalk called a footstalk or petiole. When the form or dimensions of a leaf are spoken of, it is generally the blade that is meant, without the petiole or stalk.
36. The end by which a leaf, a part of the flower, a seed, or any other organ, is attached to the stem or other organ, is called its base, the opposite end is its apex or summit, excepting sometimes in the case of anther-cells (115).
37. Xjeaves are
sessile, when the blade rests on the stem without the intervention of a petiole. amplexicaul or stem- clasping, when the sessile base of the blade clasps the stem horizontally.
perfoliate, when the base of the blade not only clasps the stem, but closes round it on the opposite side, so that the stem appears to pierce through the blade. decurrent, when the edges of the leaf are continued down the stem so as to form raised lines or narrow appendages, called wings.
sheathing, when the base of the blade, or of the more or less expanded petiole, fonus a vertical sheath roimd the stem for some distance above the node.
38. Leaves and flowers are called radical, wlien inserted on a rhizome or stock, or so close to the base of the stem as to appear to proceed from the root, rhizome, or stock; caulitie, when inserted on a distinct stem. Radical leaves are rosulate when they spread in a cu'cle on the ground.
39. Leaves are
simple and entire, when the blade consists of a single piece, with the margin no- where indented, simple being used in opposition to compound, entire m opposition to dentate, lohed, or divided.
ciliate, when bordered with thick hairs or fine hair-like teeth.
dentate or toothed, when the margin is only cut a httle way in, into what have been compared to teeth. Such leaves are serrate, when the teeth are regular and pointed like the teeth of a saw; crenate, when regular and blunt or romided (com- pai'ed to the battlements of a tower); serrulate, and crenulate, when the serratures or crenatures are small; sinuate, when the teeth are broad, not deep, and n-regular (compared to bays of the coast); wavy or undulate, when the edges are not flat, but bent up and down (compared to the waves of the sea).
lohed or cleft, when more deeply indented or divided, but so that the incisions do not reach the midrib or petiole. The portions thus divided take the name of lohes. When the lobes are narrow and very irregular, the leaves are said to be laciniate. The spaces between the teeth or lobes are called sinuses.
divided or dissected, when the incisions reach the midrib or petiole, but the parts so divided off, called segments, do not separate from the petiole, even when the leaf falls, without tearing.
compound, when divided to the midrib or petiole, and the parts so divided off, called leaflets, separate, at least at the fall of the leaf, from the petiole, as the whole leaf does from the stem, without tearing. The common stalk upon which the leaflets are inserted is called the com^non petiole or the rhachis; the separate stalk of each leaflet is a petiolule.
40. Leaves are more or less marked by veins, which, starting from the stalk, diverge or branch as the blade widens, and spread all over it more or less visibly. The principal ones, when prominent, are often called ribs or nerves, the smaller branches only then retaining the name of veins, or the latter are termed veinlets. The smaller veins are often connected together like the meshes of a net, they are then said to anastomose, and the leaf is said to be reticulate or net-veined. When one principal vein runs direct from the stalk towards the summit of the leaf, it is called the midrib. When several start from the stalk, diverge slightly without branching, and converge again towards the summit, they are said to be parallel, although not mathematically so, Wlien 8 or 5 or more ribs or nerves diverge from the base, the leaf is said to be ^-nerved, ^-nerved, etc., but if the lateral ones diverge from the midrib a little above the base, the leaf is triplinerved, quintuplinerved, etc. The arrangement of the veins of a leaf is called their venation.
41. The Leaflets, Segments, Lobes, or "Veins of leaves are pinnate (feathered), when there are several succeeding each other on each side of the midi'ib or petiole, compai'ed to the branches of a feather. A pinnately lobed or divided leaf is called lyrate when the terminal lobe or segment is much larger and broader than the lateral ones, compared, by a stretch of imagination, to a lyre; runcinate, when the lateral lobes are curved backwards towards the base of the leaf; pectinate, when the lateral lobes are numerous, narrow, and regular, like the teeth of a comb.
palmate or digitate, when several diverge from the same point, compared to the fingers of the hand.
ternate, when three only start from the same point, in which case the distinction between the palmate and pinnate arrangement often ceases, or can only be determined by analogy with allied plants. A leaf with ternate lobes is called trifid. A leaf with three leaflets is sometimes improperly called a ternate leaf: it is the leaflets that are ternate; the whole leaf is trifoliolate. Ternate leaves are leaves growing three together.
pedate, when the division is at first ternate, but the two outer branches are forked, the outer ones of each fork again forked, and so on, and all the branches are near together at the base, compared vaguely to the foot of a bird.
42. Leaves with pinnate, palmate, pedate, etc., leaflets, are usually for shortness called pinnate, palmate, pedate, etc., leaves. If they are so cut into segments only, they are usually said to be pinnatisect, palmatisect, pedatisect, etc., although the distinction between segments and leaflets is often unheeded in descriptions, and cannot indeed always be ascertained. If the leaves are so cut only into lobes, they are said to be pinnatifid, palmatifid, pedatifid, etc.
43. The teeth, lobes, segments, or leaflets, may be again toothed, lobed, divided, or compounded. Some leaves are even three or more times divided or compounded. In the latter case they are termed decompound. When twice or thrice pinnate (bipinnate or tripinnate), each primary or secondary division, with the leaflets it comprises, is called a pinna. When the pinna of a leaf or the leaflets of a pinna are in pairs, without an odd terminal pinna or leaflet, the leaf or pinna so divided is said to be abruptly pinnate; if there is an odd terminal pinna or leaflet, the leaf or pinna is unequally pinnate (imparipinnatum).
44. The number of leaves or their parts is expressed adjectively by the following numerals, derived from the Latin:—
prefixed to a termination, indicating the particular kind of part referred to. Thus—
unidentate, bidentate, multidentate, mean one-toothed, two-toothed, many-toothed, etc.
bifid, trifid, multifid, mean two-lobed, three-lobed, many-lobed, etc.
unifoliolate, bifoliolate, multifoliolate, mean having one leaflet, two leaflets, many leaflets, etc.
unifoliate, bifoliate, multifoliate, mean having one leaf, two leaves, many leaves, etc.
biternate and triternate, mean twice or thrice ternately divided.
unijugate, bijugate, multijugate, etc., pinnæ or leaflets, mean that they are in one, two, many, etc., pairs (juga).
45. Leaves or their parts, when flat, or any other flat organs in plants, are linear, when long and narrow, at least four or five times as long as broad, falsely compared to a mathematical line, for a linear leaf has always a perceptible breadth.
lanceolate, when about three or more times as long as broad, broadest below the middle, and tapering towards the summit, compared to the head of a lance.
cuneate, when broadest above the middle, and tapering towards the base, compared to a wedge with the point downwards; when very broadly cuneate and rounded at the top, it is often called flabelliform or fan-shaped.
spathulate, when the broad part near the top is short, and the narrow tapering part long, compared to a spatula or flat ladle.
ovate, when scarcely twice as long as broad, and rather broader below the middle, compared to the longitudinal section of an egg; obovate is the same form, with the broadest part above the middle.
orbicular, oval, oblong, elliptical, rhomboidal, etc., when compared to the corresponding mathematical figures.
transversely oblong, or oblate, when conspicuously broader than long.
falcate, when curved like the blade of a scythe.
46. Intermediate forms between any two of the above are expressed by combining two terras. Thus, a linear-lanceolate leaf is long and narrow, yet broader below the middle, and tapering to a point ; a linear-oblong one is scarcely narrow enough to be called linear, yet too narrow to be strictly oblong, and does not conspicuously taper either towards the summit or towards the base. . The apex or summit of a leaf is acute or 'pointed^ when it foi'ms an acute angle or tapers to a point. ohtuse or blunt, when it forms a very obtuse angle, or more generally when it is more or less rounded at the top. acuminate or cuspidate^ when suddenly narrowed at the top, and then more or less prolonged into an acumen or point, wliich may be acute or obtuse, linear or tapering. Some botanists make a slight difference between the acuminate and cuspidate apex, the acumen being more distmct from the rest of the leaf in the latter case than in the former ; but in general the two terms are used in the same sense, some preferring the one and some the other. truncate, when the end is cut off square. retuse, when very obtuse or truncate, and sUghtly indented. emarginate or notched, when more decidedly indented at the end of the midrib ; obeordate, if at the same time approaching the shape of a heart vrith its point down- wards. mucronaie, when the midrib is produced beyond the apex in the form of a small point. arisfate, when the point is fine like a hair. . The base of the leaf is hable to the same variations of form as the apex, but the terms more commonly used are tapering or narroived for acute and acuminate, rounded for obtuse, and cordate for emarginate. In all cases the petiole or point of attachment prevent ahy such absolute termination at the base as at the apex. . A leaf may be cordate at the base whatever be its length or breadth, or what- ever the shape of the two lateral lobes, caUed auricles (or little ears), formed by the indenture or notch, but the term cordiform or heart-shaped leaf is restricted to an ovate and acute leaf, cordate at the base, with rounded auricles. The word auricles is more particularly used as applied to sessile and stem-clasping leaves. . If the auricles are pointed, the leaf is more particularly called auriculate ; it is moreover said to be sagittate, when the points are directed downwards, compared to an arrow-head ; hastate, when the points diverge horizontally, compared to a halbert. . A reniform leaf is broader than long, slightly but broadly cordate at the base, with rounded auricles, compared to a kidney. . In a peltate leaf, the stalk, instead of proceeding from the lower edge of the blade, is attached to the under surface, usually near the lower edge, but sometimes in the very centre of the blade. The peltate leaf has usually several principal nerves radiating from the point of attachment, being, in fact, a cordate leaf, with the auricles united. . All these modifications of division and form in the leaf pass so gradually one into the other that it is often difficult to say which term is the most applicable — whether the leaf be toothed or lobed, divided or compound, oblong or lanceolate, obtuse or acute, etc. The choice of the most apt expression will depend on the skill of the describer. . laeaves, when solid, Stems, Fruits, Tubers, and other parts of plants, when not flattened Hke ordinary leaves, are setaceous or capillary, when very slender hke bristles or hairs. acicular, when very slender, but stiff and pointed like needles. subulate, when rather thicker and firmer like awls. linear, when at least four times as long as thick ; oblong, when from about two to about four times as long as thick, the terms having the same sense as when apphed to flat siu'faces. ovoid, when egg-shaped, with the broad end downwards, obovoid if the broad end is upwards ; these terms corresponding to ovate and obovate shapes in flat surfaces. globular or spherical, when corresponding to orbicular in a flat siu-face. Round applies to both. turbinate, when shaped like a top.
conical, when tapering upwards ; obconical, when tapering downwards, if in both cases a transverse section shows a circle.
pt/ramidal, when tapering upwards ; ohpyramidal^ when tapering downwards, if in both cases a transverse section shows a triangle or polygon. fusiform^ or spindle-shaped, wlien tapering at both ends ; cylindrical, when not tapering at either end, if in both cases the transverse section shows a circle, or sometimes irrespective of the transverse shape. terete, when the transverse section is not angular ; trigonous, triquetrous, if the transverse section shows a triangle, irrespective in both cases of longitudinal form. compressed, when more or less flattened laterally ; depressed, when more or less flattened vertically, or at any rate at the top ; ohcompressed (in the achenes of Compodtce), when flattened from front to back. articulate ov jointed, if at any period of their growth (usually when fully formed and approaching their decay, or in the case of fruits when quite ripe) they separate, without tearing, into two or more pieces placed end to end. The joints where they separate are called articulations, each separate piece an article. The name oi joint is, in common language, given both to the articulation and the article, but more especially to the former. Some morlern botanists, however, propose to restrict it to the article, giving the name o^ joining to the articulation.
didymoiis, when sh'ghtly two-lobed, with rounded obtuse lobes. moniliform, or beaded, when much contracted at regular intervals, but not sepa- rating spontaneously into articles.
55. In their consistence laeaves or other organs are fleshy, when thick and soft ; succulent is generally used in the same sense, but implies the presence of more juice. coriaceous, when firm and dry, or very tough, of the consistence of leather. membranous, when thin and not stiff. scarious or scariose, when very thin, more or less transparent and not green, yet rather stiff.
56. The terms apphed botanically to the consistence of solids are thos3 in general use in common language.
57. The mode in which unexpanded leaves are disposed in the leaf-bud is called their vernation or prcefoliation ; it varies considerably, and technical terms have been proposed to express some of its varieties, but it has been hitherto rarely noticed in descriptive botany.