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.

[Illustration: 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.

[Illustration: Fig. 172. Leaves of Solanum jasminoides, the petiole
adapted for climbing.]

[Illustration: Fig. 173. Leaf of Lathyrus Aphaca, consisting of a pair
of stipules and a tendril.]

168. =Leaves for Climbing= are various in adaptation. True
foliage-leaves serve this purpose; as in Gloriosa, where the attenuated
tip of a simple leaf (otherwise like that of a Lily) hooks around a
supporting object; or in Solanum jasminoides of the gardens (Fig. 172),
and in Maurandia, etc., where the leaf-stalk coils round and clings to a
support; or in the compound leaves of Clematis and of Adlumia, in which
both the leaflets and their stalks hook or coil around the support.

169. Or in a compound leaf, as in the Pea and most Vetches, and in
Cobaea, while the lower leaflets serve for foliage, some of the uppermost
are developed as tendrils for climbing (Fig. 167). In the common Pea
this is so with all but one or two pairs of leaflets.

170. In one European Vetch, the leaflets are wanting and the whole
petiole is a tendril, while the stipules become the only foliage (Fig.
173).

171. =Leaves as Pitchers=, or hollow tubes, are familiar in the common