SPINES OE THORNS. 



119 



buds in certain circumstances. Even roots, when long exposed to the 

 air,_ may thus assume the functions of stems. Leaves bearing buds on 

 their margin are called proliferous (proks, offspring, and fero, I bear). 



Spines or Thoens. Branches 

 are sometimes arrested in their 

 development, and, in place of 

 forming leaves, become trans- 

 formed into spines and tendrils. 

 Spines or thorns are undeveloped 

 branches, ending in more or less 

 pointed extremities, as in the 

 Hawthorn. Plants which have 

 spines in a wild state, as the 

 Apple and Pear, often lose them 

 when cultivated, in consequence 

 of their being changed into 

 branches ; in some cases, as in 

 Prunus spinosa, or the Sloe 

 (fig. 234), a branch bears leaves 

 at its lower portions, and terminates 



Fig. 234. 



rig. 235. 



in a spine. Leaves them- 



Fig. 236. 



Fig. 237. 



Fig. 238. 



Fig. 234. Branch of Pniniis spinosa, or Sloe, with alternate leaves, and ending in a spine 

 or thorn. Fig. 235. Pinnate leaf of Astragalus massUiensis, the midrib of which, r, ends 

 in a spine, s, Petiolary stipules. /, Nine pairs of leaflets. Fig. 236. Branch ,of Berberis 

 vulgaris, or Barberry, the leaves of which, ///, are transformed into branching spines. In 

 the axil of each, a cluster, r rr, of regularly formed leaves is developed. Fig, 237. Base 

 of the pinnate leaf of Robinia pseudacacia, the stipules of which, s 5, are converted into 

 spines or thorns. &, Branch, r. Petiole. Fig. 238. Branch of Ribes Uva-crispa, in which 

 the pulvinus or swelling, c c c, at the base of each of the leaves, ///, is changed into a spine, 

 which is either simple, or double, or triple, h &, Leaf-buds arising from the axil of the 

 leaves. 



