unequally pinnate because there is an odd leaflet at the end of the common petiole. When the odd leaflet is absent the leaf is equally or abruptly pinnate. A leaf becomes twice pinnate (bi-pinnate) when the common petiole, instead of bearing leaflets, bears secondary petioles upon which the leaflets are pinnately arranged. When leaflets are arranged on the digitate plan, and are but 3 in number, they are called ternate, and the leaf

FIG. 47.-Digitate leaf of Horse Chestnut.

is tri-foliolate, as in Clover and Strawberry; if 5, quinate, the leaf being quinque-foliolate. The leaflets may be twice ternate (bi-ternate) if the petiole bears 3 secondary petioles, each of which bears 3 leaflets, and so on.

II. The point of a leaf or leaflet at which the midrib ends is called the apex; the point where it passes into the petiole, or, if the leaf be sessile, where it is joined to the stem, the base. The apex and base vary considerably

in outline, and attention must be paid to both in describing the form of leaves. The apex, if sharp, is termed acute, if blunt or rounded, obtuse; if with a very shallow narrow notch, emarginate; if the notch be deep, bifid-the leaf becoming bipartite if divided nearly to the base; it is trifid or tripartite if there be three divisions. The base of the blade in cordate, sagittate, and hastate leaves we have already figured. If the base of the sessile leaf clasp the stem, it is termed amplexicaul. If the lobes at each side of the base of an amplexicaul leaf be united together on the side of the stem opposite to the midrib, so that the stem appears to pass through the blade, the leaf is perfoliate. If the bases of two opposite leaves be united

stip.

Stip.

FIG. 48.-Pinnate leaf of Bean. Stip. stipules.

on each side of the stem, as in Teazle, the leaves are said to be connate. Sometimes, in sessile leaves, the margins of the blade are continued down the sides of the stem, forming wings to it. Such leaves are decurrent. They are very common amongst Thistles. When the petiole joins the blade upon its under surface and not at the margin, as in Garden Nasturtium (Tropœolum), the leaf is said to be peltate.

The margin of the leaf varies, being sometimes perfectly continuous and not indented or toothed at all, when it is termed entire; it is serrate if with sharp teeth directed forward, like those of a saw ; dentate if with sharp teeth directed outward; crenate if with rounded teeth.

The surface may be more or less hairy, or altogether without hairs, when it is termed glabrous. Different terms are used to denote different kinds and degrees of hairiness, the more important of which are defined in the Glossary at the end of the book.

12. Taking up again a specimen of the Pea or Bean, observe on each side of the base of the petiole a leafy organ somewhat resembling a leaflet. In the Pea these organs are very large-larger indeed than the leaflets. They are relatively very large also in the Garden Pansy. These are the stipules. They originate as lateral appendages of the leaf-base, and usually attain their full development before the leaf to which they belong. Leaves provided with stipules are called stipulate, and leaves destitute of them, as those of Wallflower, exstipulate. Like leaves and leaflets, the stipules vary in form, but they are generally small, and often fall away very early, as in the Oak and Beech.

13 Foliage-leaves are sometimes curiously modified, either to serve some special purpose, or by the absence of the blade, or the reduction of the leaf to a mere spine. Thus in the Pea we find the extremity of the common petiole and two or more of the lateral leaflets assume the form of tendrils, enabling the weak stem to lay hold of supports in climbing. Compare with the tendrils of the Pea those of the Grape-vine or Virginian Creeper, which we have described as branches modified for the same purpose (page 59).

In Barberry, the leaves borne by the elongated branches

are reduced to sharp spines, from the axils of which spring subsessile tufts of ordinary foliage-leaves, borne (as in Pine, Larch and Cedar) upon branches with undeveloped internodes. Leaves tufted in this way are said to be fasciculate. In Whin or Furze, both the leaves (excepting those of the very young plant) and the branches are spinose. Stipules also are sometimes replaced by spines. When the blade of the leaf is absent, the petiole sometimes becomes flattened to such an extent as to look

FIG. 49.-Branch of Acacia melanoxylon. The lower leaves with pinnate lamina; the upper reduced to petioles (phyllodes).

like an entire leaf, in order to replace the blade as an organ useful to the plant. But the flattening is generally vertical, so that the apparent leaf is placed edgewise upon the stem, instead of spreading horizontally. By this character these leaf-life petioles may be generally recognised. They are called phyllodes. Sometimes the true blade is partially developed at the extremity of the phyllode, thus putting its petiolar character beyond doubt,

14. We cannot fail to have observed the various ways in which the flowers are borne upon the stem, in gathering and comparing together the common plants which we have had occasion to use in the course of these lessons. It is convenient to speak of the Flowering System, or mode of arrangement of the flowers of plants, as the

INFLORESCENCE.

In the Tulip we find a solitary terminal flower, borne by a firm herbaceous peduncle, which appears to spring directly from the root. (Such radical peduncles, whether they bear one flower or many as in the Cowslip and Dandelion, are called scapes.)

In Wallflower, the peduncle, instead of ending in a solitary flower, gives off successively a number of shortstalked (pedicellate) flowers in succession, until it exhausts itself and ceases to lengthen. Such an infloresence is termed a raceme.

Common Plantain, gathered to feed canary-birds, has a similar kind of infloresence, but the flowers are sessile. This difference distinguishes the spike from the raceme. The corymb is a form of raceme in which the lower pedicels are much longer than the upper ones.

In Cow-parsnip and Carrot the flowers are borne upon pedicels springing apparently from one point. Such an arrangement of pedicellate flowers constitutes the umbel. But as you find each of the umbels in these plants borne upon peduncles, which, like the pedicels, also spring from one point, the entire inflorescence forms a compound umbel; the umbels of single flowers being the partial umbels.

Observe the ring of small leaves at the base of the pedicels in the Carrot, forming an involucre. In compound umbels we frequently have both general and partial involucres, the former surrounding the compound umbel, the latter each partial umbel.

Suppose, now, all the flowers of a simple umbel to be sessile; we should have the same form of inflorescence as we find in the Daisy and Marigold, in which a number of florets are arranged upon a conical or flattened disk (the common receptacle), surrounded by an involucre. Such an inflorescence may be called a flower-head. The older botanists used to regard the flower-head as a kind