stem. The second and third pairs of leaves on the axillary shoot (when the latter develops) are reduced to scales, which decussate with the spines. True leaves follow the scales. PROTECTION BY THE LEAF-BASE OR THE LEAF-STALK The axillary buds are thus protected in most Composites, Umbellifers, in the whole family of the Caryophyllaceae (Pink family), except Spergula and Spergularia, in the Gentians, and many other families. In all these species the base of the petiole is more or less dilated, so as the more effectually to protect the bud. B S FIG. 110.-SECTION ACROSS Fig. 110 represents a section across the stem of a Walnut (Juglans nigra). It shows the bud, B, lying between the stem, S, and the dilated base of the leaf-stalk, L. The protection is more complete than the figure indicates, because in nature the parts touch, while for clearness a small space has been left between them in the illustration. In the Box Elder (Negundo aceroides) (figs. 111,112), a near ally of the Maples, the base of the petiole is also widened, concave, almost covering the axillary bud, and attached to the axis by a wide and deeply horseshoe-shaped base. The interior of the concavity is densely lined with white silky hairs, which almost completely surround the axillary bud, keeping it safe and comfortable till the fall of the leaf. The terminal bud nestles in the cavity between the petioles of the youngest expanded or expanding pair of leaves. The petioles of the latter remain erect for a considerable time, and being closely applied face to face, FIG. 111.-Portion of shoot (A) with the bases of the two opposite leaf-stalks (P). FIG. 112.-Vertical section of same, showing the axillary buds (B) sheltered in the hollowed base of the leaf-stalk. they completely cover and protect the bud. When growth becomes arrested for the season the terminal bud attains some size, so that its tip projects beyond the cavity of the petioles. By this time, however, the scales of the winter-bud are sufficiently hardened to escape harm and protect the younger members. In Sophora japonica (fig. 113), one of the Leguminosa, the terminal bud is thickly covered with brown hairs, and is also protected by the crowding of the leaves and the stipules. The latter are narrowly linear or setaceous and caducous, i.e., falling early. The axillary bud is entirely protected by the swollen, fleshy base of the petiole. The resting bud remains very small during winter, and consists of leaves and stipules, crowded together, and densely covered with short, brown hairs. In Citharexylum quadrangulare (fig. 114), belonging to the Verbenacea, an exstipulate family, the axillary buds are completely covered by the concave pedestal. . B P" FIG. 113.-SOPHORA JAPONICA. Two nodes of a stem, the lower showing the base of the petiole (P') with the small round scar of the fallen stipule. In vertical section above, the upper node showing the axillary bud (B) completely covered by the thickened, fleshy base of the petiole (p"). The terminal bud in the growing state consists of leaves partly conduplicate, then involute at the margins, and placed face to face, but not overlapping or interlocking with one another. The leaves attain some size before expanding, and each pair covers the next younger pair. In some cases the petiole forms a regular arch over the bud, as, for instance, in Rhus glabra (fig. 115). Additional protection is also afforded by hairs, both on the bud and on the under side of the cup formed by the petiole. In these cases the overarching tissue belongs entirely to the petiole. In others the stem also projects outwards, and thus makes the protection more complete. FIG. 114.-CITHAREXYLUM QUADRANGULARE. Nat. size. ax, ar, axis of shoot with portions of a pair of leaves; a a, articulation of the leaves, 7, 7, to the persistent sheathing pedestals, one of which, p, is slightly opened to show the axillary bud it covers. In Kalmia latifolia, for instance (figs. 116-119), the axis of every shoot produces an outgrowth opposite the dilated portion of the petiole. This is carried still further in Actinidia colomicta (fig. 120), where, as Feist (13) has shown, the bark of Section through a bud shortly before the leaf falls. S, stem; FIG. 116. S S FIG. 117. SHOOT OF KALMIA LATIFOLIA, × 2. FIG. 116.-s, swelling of the stem just above the base of the leaf (L), between which and the leaf-base the bud is sheltered. FIG. 117.-Another view. Sc, scar of leaf; s, swelling; B bud. |