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121. This is tautological; for foliage is simply leaves: but it is very convenient to speak of typical leaves, or those which serve the plant for assimilation, as foliage-leaves, or ordinary leaves. These may first be considered.

122. The Parts of a Leaf. The ordinary leaf, complete in its parts, consists of blade, foot-stalk, or petiole, and a pair of stipules.

123. First the Blade or Lamina, which is the essential part of ordinary leaves, that is, of such as serve the purpose of foliage. In structure it consists of a softer part, the green pulp, called parenchyma, which is traversed and supported by a fibrous frame, the parts of which are called ribs or veins, on account of a certain likeness in arrangement to the veins of animals. The whole surface is covered by a transparent skin, the Epidermis, not unlike that which covers the surface of all fresh shoots.

124. Note that the leaf-blade expands horizontally—that is, normally presents its faces one to the sky, the other to the ground, or when the leaf is erect the upper face looks toward the stem that bears it, the lower face away from it. Whenever this is not the case there is something to be explained.

125. The framework consists of wood—a fibrous and tough material which runs from the stem through the leaf-stalk, when there is one, in the form of parallel threads or bundles of fibres; and in the blade these spread out in a horizontal direction, to form the ribs and veins of the leaf. The stout main branches of the framework are called the Ribs. When there is only one, as in Fig. 112, 114, or a middle one decidedly larger than the rest, it is called the Midrib. The smaller divisions are termed Veins; and their still smaller subdivisions, Veinlets. The latter subdivide again and again, until they become so fine that they are invisible to the naked eye. The fibres of which they are composed are hollow; forming tubes by which the sap is brought into the leaves and carried to every part.

Fig. 112. Leaf of the Quince: b, blade; p, petiole; st, stipules.

126. Venation is the name of the mode of veining, that is, of the way in which the veins are distributed in the blade. This is of two principal kinds; namely, the parallel-veined, and the netted-veined.

127. In Netted-veined (also called Reticulated) leaves, the veins branch off from the main rib or ribs, divide into finer and finer veinlets, and the branches unite with each other to form meshes of network. That is, they anastomose, as anatomists say of the veins and arteries of the body. The Quince-leaf, in Fig. 112, shows this kind of veining in a leaf with a single rib. The Maple, Basswood, Plane or Buttonwood (Fig. 74) show it in leaves of several ribs.

128. In parallel-veined leaves, the whole framework consists of slender ribs or veins, which run parallel with each other, or nearly so, from the base to the point of the leaf—not dividing and subdividing, nor forming meshes, except by minute cross-veinlets. The leaf of any grass, or that of the Lily of the Valley (Fig. 113) will furnish a good illustration. Such parallel veins Linnæus called Nerves, and parallel-veined leaves are still commonly called nerved leaves, while those of the other kind are said to be veined—terms which it is convenient to use, although these "nerves" and "veins" are all the same thing, and have no likeness to the nerves and little to the veins of animals.

129. Netted-veined leaves belong to plants which have a pair of seed-leaves or cotyledons, such as the Maple (Fig. 20, 24), Beech (Fig. 33), and the like; while parallel-veined or nerved leaves belong to plants with one cotyledon or true seed-leaf; such as the Iris (Fig. 59), and Indian Corn (Fig. 70). So that a mere glance at the leaves generally tells what the structure of the embryo is, and refers the plant to one or the other of these two grand classes—which is a great convenience. For when plants differ from each other in some one important respect, they usually differ correspondingly in other respects also.

Fig. 113. A (parallel-veined) leaf of the Lily of the Valley. 114. One of the Calla Lily.

130. Parallel-veined leaves are of two sorts—one kind, and the commonest, having the ribs or nerves all running from the base to the point of the leaf, as in the examples already given; while in another kind they run from a midrib to the margin, as in the common Pickerel-weed of our ponds, in the Banana, in Calla (Fig. 114), and many similar plants of warm climates.

131. Netted-veined leaves are also of two sorts, as in the examples already referred to. In one case the veins all rise from a single rib (the midrib), as in Fig. 112, 116-127. Such leaves are called Feather-veined or Penni-veined, i.e. Pinnately-veined; both terms meaning the same thing, namely, that the veins are arranged on the sides of the rib like the plume of a feather on each side of the shaft.

132. In the other case (as in Fig. 74, 129–132), the veins branch off from three, five, seven, or nine ribs, which spread from the top of the leaf-stalk, and run through the blade like the toes of a web-footed bird. Hence these are said to be Palmately or Digitately veined, or (since the ribs diverge like rays from a centre) Radiate-veined.

133. Since the general outline of leaves accords with the framework or skeleton, it is plain that feather-veined (or penni-veined) leaves will incline to elongated shapes, or at least to be longer than broad; while in radiate-veined leaves more rounded forms are to be expected. A glance at the following figures shows this.

Fig. 115–120. A series of shapes of feather-veined leaves.

134. Forms of Leaves as to General Outline. It is necessary to give names to the principal shapes, and to define them rather precisely, since they afford easy marks for distinguishing species. The same terms are used for all other flattened parts as well, such as petals; so that they make up a great part of the descriptive language of Botany. It will be a good exercise for young students to look up leaves answering to these names and definitions. Beginning with the narrower and proceeding to the broadest forms, a leaf is said to be

Linear (Fig. 115), when narrow, several times longer than wide, and of the same breadth throughout.

Lanceolate, or Lance-shaped, when conspicuously longer than wide, and tapering upwards (Fig. 116), or both upwards and downwards.

Oblong (Fig. 117), when nearly twice or thrice as long as broad.

Elliptical (Fig. 118) is oblong with a flowing outline, the two ends alike in width.

Oval is the same as broadly elliptical, or elliptical with the breadth considerably more than half the length.

Ovate (Fig. 119), when the outline is like a section of a hen's egg lengthwise, the broader end downward.

Orbicular, or Rotund (Fig. 132), circular in outline, or nearly so.

Fig. 121, oblanceolate; 122, spatulate; 123, obovate; and 124, wedge-shaped, feather-veined, leaves.

135. A leaf which tapers toward the base instead of toward the apex may be

Oblanceolate (Fig. 121) when of the lance-shaped form, only more tapering toward the base than in the opposite direction.

Spatulate (Fig. 122) when more rounded above, but tapering thence to a narrow base, like an old-fashioned spatula.

Obovate (Fig. 123) or inversely ovate, that is, ovate with the narrower end down.

Cuneate or Cuneiform, that is, Wedge-shaped (Fig. 124), broad above and tapering by nearly straight lines to an acute angle at the base.

Fig. 125, sagittate; 126, auriculate; and 127, halberd-shaped or hastate leaves.

136. As to the Base, its shape characterizes several forms, such as

Cordate or Heart-shaped (Fig. 120, 129), when a leaf of an ovate form, or something like it, has the outline of its rounded base turned in (forming a notch or sinus) where the stalk is attached.

Reniform, or Kidney-shaped (Fig. 131), like the last, only rounder and broader than long.

Auriculate, or Eared, having a pair of small and blunt projections, or ears, at the base, as in one species of Magnolia (Fig. 126).

Sagittate, or arrow-shaped, where such ears are acute and turned downwards, while the main body of the blade tapers upwards to a point, as in the common Sagittaria or Arrow-head, and in the Arrow-leaved Polygonum (Fig. 125).

Hastate, or Halberd-shaped, when such lobes at the base point outwards, giving the shape of the halberd of the olden time, as in another Polygonum (Fig. 127).

Fig. 128–132. Various forms of radiate-veined leaves.

Peltate, or Shield-shaped (Fig. 132), is the name applied to a curious modification of the leaf, commonly of a rounded form, where the footstalk is attached to the lower surface, instead of the base, and therefore is naturally likened to a shield borne by the outstretched arm. The common Watershield, the Nelumbium, and the White Water-lily, and also the Mandrake, exhibit this sort of leaf. On comparing the shield-shaped leaf of the common Marsh Pennywort (Fig. 132) with that of another common species (Fig. 130), it is at once seen that a shield-shaped leaf is like a kidney-shaped (Fig. 130, 131) or other rounded leaf, with the margins at the base brought together and united.

137. As to the Apex, the following terms express the principal variations:—

Acuminate, Pointed, or Taper-pointed, when the summit is more or less prolonged into a narrowed or tapering point; as in Fig. 133.

Acute, ending in an acute angle or not prolonged point; Fig. 134.

Obtuse, with a blunt or rounded apex; as in Fig. 135, etc.

Truncate, with the end as if cut off square; as in Fig. 136.

Retuse, with rounded summit slightly indented, forming a very shallow notch, as in Fig. 137.

Emarginate, or Notched, indented at the end more decidedly; as in Fig. 138.

Obcordate, that is, inversely heart-shaped, where an obovate leaf is more deeply notched at the end (Fig. 139), as in White Clover and Wood-sorrel; so as to resemble a cordate leaf inverted.

Cuspidate, tipped with a sharp and rigid point; as in Fig. 140.

Mucronate, abruptly tipped with a small and short point, like a mere projection of the midrib; as in Fig. 141.

Aristate, Awn-pointed, and Bristle-pointed, are terms used when this mucronate point is extended into a longer bristle-form or slender appendage.

The first six of these terms can be applied to the lower as well as to the upper end of a leaf or other organ. The others belong to the apex only.

Fig. 133–141. Forms of the apex of leaves.

138. As to degree and nature of Division, there is first of all the difference between

Simple Leaves, those in which the blade is of one piece, however much it may be cut up, and

Compound Leaves, those in which the blade consists of two or more separate pieces, upon a common leaf-stalk or support. Yet between these two kinds every intermediate gradation is to be met with.

Fig. 142–147. Kinds of margin of leaves.

139. As to Particular Outlines of Simple Leaves (and the same applies to their separate parts), they are

Entire, when their general outline is completely filled out, so that the margin is an even line, without teeth or notches.

Serrate, or Saw-toothed, when the margin only is cut into sharp teeth, like those of a saw, and pointing forwards; as in Fig. 142.

Dentate, or Toothed, when such teeth point outwards, instead of forwards; as in Fig. 143.

Crenate, or Scalloped, when the teeth are broad and rounded; as in Fig. 144.

Repand, Undulate, or Wavy, when the margin of the leaf forms a wavy line, bending slightly inwards and outwards in succession; as in Fig. 145.

Sinuate, when the margin is more strongly sinuous or turned inwards and outwards; as in Fig. 146.

Incised, Cut, or Jagged, when the margin is cut into sharp, deep, and irregular teeth or incisions; as in Fig. 147.

Lobed, when deeply cut. Then the pieces are in a general way called Lobes. The number of the lobes is briefly expressed by the phrase two-lobed, three-lobed, five-lobed, many-lobed, etc., as the case may be.

140. When the depth and character of the lobing needs to be more particularly specified, the following terms are employed, viz.:—

Lobed, in a special sense, when the incisions do not extend deeper than about half-way between the margin and the centre of the blade, if so far, and are more or less rounded; as in the leaves of the Post-Oak, Fig. 148, and the Hepatica, Fig. 152.

Cleft, when the incisions extend half way down or more, and especially when they are sharp; as in Fig. 149, 153. And the phrases two-cleft, or, in the Latin form, bifid, three-cleft or trifid, four-cleft or quadrifid, five-cleft or quinquefid, etc., or many-cleft, in the Latin form, multifid—express the number of the Segments, or portions.

Parted, when the incisions are still deeper, but yet do not quite reach to the midrib or the base of the blade; as in Fig. 150, 154. And the terms two-parted, three-parted, etc., express the number of such divisions.

Divided, when the incisions extend quite to the midrib, as in the lower part of Fig. 151, or to the leaf-stalk, as in Fig. 155; which really makes the leaf compound. Here, using the Latin form, the leaf is said to be bisected, trisected (Fig. 155), etc., according to the number of the divisions.