Fig. 170. Series of bud-scales and foliage-leaves from a developing bud of the Low Sweet Buckeye (Æsculus parviflora), showing nearly complete gradation, from a scale to a compound leaf of five leaflets; and that the scales answer to reduced petioles.
[166.] Leaves as Bud-Scales serve to protect the forming parts within. Having fulfilled this purpose they commonly fall off when the shoot develops and foliage-leaves appear. Occasionally, as in Fig. [170], there is a transition of bud-scales to leaves, which reveals the nature of the former. The Lilac also shows a gradation from bud-scale to simple leaf. In Cornus florida (the Flowering Dogwood), the four bud-scales which through the winter protect the head of forming flowers remain until blossoming, and then the base of each grows out into a large and very showy petal-like leaf; the original dry scale is apparent in the notch at the apex.
Fig. 171. Shoot of common Barberry, showing transition of foliage-leaves to spines.
[167.] Leaves as Spines occur in several plants. A familiar instance is that of the common Barberry (Fig. [171]). In almost any summer shoot, most of the gradations may be seen between the ordinary leaves, with sharp bristly teeth, and leaves which are reduced to a branching spine or thorn. The fact that the spines of the Barberry produce a leaf-bud in their axil also proves them to be leaves.
Fig. 172. Leaves of Solanum jasminoides, the petiole adapted for climbing.