Fig. 25.—Compound leaf of the Rose. L, leaflets; P, leaf-stalk; st, stipules. (× ½) Fig. 26.—Compound leaf of the Horse Chestnut. (× ⅙) The compound leaf of the horse chestnut (Fig. 26) is of a different type, for the seven leaflets all arise from one point; and the leaves of the lupine (Fig. 9) are arranged on the same plan. When the venation is examined, the reason for this becomes plain. In these cases the main veins all diverge from the top of the leaf stalk; whereas in the rose and ash the midrib gives rise to side ribs in pairs. The leaflets are naturally arranged so that one of the larger veins shall support each. The next question arising is, “What causes the differences in the methods of branching of the midrib?” At present this is a mystery. Compound leaves consisting of three leaflets are found in woodsorrel, strawberry (Fig. 50), clover, etc. [Pg 43] Intermediate leaves.—The ivy (Fig. 27) and sycamore (Fig. 33) have leaves which seem intermediate between truly simple and truly compound leaves. From the arrangement of the veins it is seen that they approach the horse chestnut type more than that of the rose. On the other hand, if the deep indentations of the oak leaf (Fig. 113) were carried to the midrib, the simple leaf would be divided into leaflets arranged, somewhat like those of the rose or ash leaf, along the sides of the midrib. Fig. 27.—Ivy. (× ¹ ₁₀)  Fig. 28.—Compound leaf of Pea. Fl, flower-stalk; Sp, stipules; T, tendrils. (× ½) Stipules.—At the bases of many leaf stalks, close to the stem, are leaf-like outgrowths called stipules. They are well seen in the rose (Fig. 25) and pea (Fig. 28). Some leaves have a sheath at the bottom of the stalk, partially enclosing the stem. Tendrils.—The pea also affords an interesting case of leaflets [Pg 44] being modified to do special work. Here the upper leaflets seem to have remained undeveloped except for their main veins, and these have acquired a remarkable power of twining round suitable objects and so supporting the stem. Many other plants have tendrils, but these are not always modified leaflets. 8. HOW LEAVES ARE ARRANGED ON THE STEM.