SPINES OR THORNS, AND TENDRILS. 



103 



where the midrib becomes spiny after the fall of some of the leaflets; in 

 the Holly, where all the veins are so; and in the Barberry (fig. 218), 

 where some of the leaves, fff, are produced in the form of spiny 

 branches, with scarcely any parenchyma. In place of producing a lamina 

 or blade at its extremity, the petiole sometimes terminates in a spine. 

 Stipules are occasionally transformed into spines, as in Robinia pseudo- 

 acacia (fig. 219, ss), and such is also the case with the swelling or pulvinus 

 at the base of the leaf, as in Ribes Uva-crispa (fig. 220, ccc). Branches 



are sometimes arrested in their progress at an early state of their de- 

 velopment, and do not appear beyond the surface of the stem; at 

 other times, after having grown to a considerable size, they undergo 

 decay. In both instances, the lower part of the branch becomes 

 embedded and hardened among the woody layers of the stem, and 

 forms a knot. 



201. Tendrils. A leaf-bud is sometimes developed as a slender spiral 

 or twisted branch, called a tendril or cirrhus (cirrus, a curl), as in the Pas- 

 sion-flower, in which the lateral buds are thus altered with the view of 

 enabling the plant to climb. When tendrils occupy the place of leaves, 

 and appear as a continuation of the leaf-stalk, they are called petiolary, 

 as in Lathyrus Aphaca, in which the stipules perform the function of 

 true leaves. In Flagellaria indica, Methonica superba, Anthericum 



Fig. 21S. Branch of Berberis vulgaris, or Barberry, the leaves of which, ///, are transformed 

 into branching spines. In the axil of each, a cluster, r r r, of regularly formed leaves is de- 

 veloped. 



Fig. 219. Base of the pinnate leaf of Robinia pseudo-acacia, the stipules of which, s s, are 

 converted into spines or thorns, b, Branch, r, Petiole. 



Fig. 220. Branch of Ribes Uva-crispa, in which the pulvinus or swelling, ccc, at the base 

 of each of the leaves, ///, is changed into a spine, which is either simple, or double, or tripk-. 

 b 6, Leaf-buds arising from the axil of the leaves. 



