TRANSFORMATIONS OF THE LEAF. 



109 



tendrils represent the attenuated leaf-blades themselves. Again, 

 the entire leaf sometimes becomes a tendril in Lathyrus, while 

 the stipules act as leaves. 



325. The petiole of the leaf of Clematis, otherwise unchanged, 

 coils like a tendril for the support of the vine. In the Green- 

 brier, the stipules are changed to tendrils, which thus arise in 

 pairs from the base of the petioles. So probably in the Gourd. 



326. But the tendrils of the Grapevine are of a different nature. From their position 

 opposite the leaves, and the tubercles occasionally seen upon them, representing flower- 

 buds, they are inferred to be abortive, or transformed flower-stalks. 



Thorns 400, Crataegus parvifolia (thorns axillary). 401, Honey-locust. 402, Common Locust. 403, 

 Berberis u, rt, its thorus. 



327. Many plants are armed, as if for self-defence, with hard, 

 sharp-pointed, woody processes, called spines or thorns. Those 

 which are properly called spines originate from leaves. In Ber- 

 beris the spines are evidently transformed leaves, as the same 

 plant exhibits leaves in every stage of the metamorphosis. In 

 Goat's-thorn (Astragalus tragacanthus) of S. Europe, the pe- 

 tioles change to spines after the leaflets fall off. In the Locust 

 (Robinia), there is a pair of spines at the base of the petiole, in 

 place of stipules. 



328. Thorns originate from axillary bnds, and are abortive branches. This is evident 

 from their position in the Hawthorn and Osage-orange. The Apple and Pear tree in 

 their wild state produce thorns, but by cultivation become thornlese ; thai is, the axil- 

 lary buds, through better tillage, develop branches instead of thorns. The terrible 



