. Class-book of botany : being outlines of the structure, physiology, and classification of plants ; with a flora of the United States and Canada . Botany; Botany; Botany. 66 TRANSFORMATIONS OF THE LEAF. 314. The petiole of the leaf of Clematis, otherwise unclianged, coils like a tendril for the support of the vine. In the greenbriar, the stipules are changed to tendrils, which thus arise in pairs from the base of the petioles. So probably in the gourd tribe. 316. But the tendrils of the grape-vine are of ,i different nature. From their position opposite the leaves, and tho tubercles occasiona
. Class-book of botany : being outlines of the structure, physiology, and classification of plants ; with a flora of the United States and Canada . Botany; Botany; Botany. 66 TRANSFORMATIONS OF THE LEAF. 314. The petiole of the leaf of Clematis, otherwise unclianged, coils like a tendril for the support of the vine. In the greenbriar, the stipules are changed to tendrils, which thus arise in pairs from the base of the petioles. So probably in the gourd tribe. 316. But the tendrils of the grape-vine are of ,i different nature. From their position opposite the leaves, and tho tubercles occasionally seen upon them, representing flower buds, they are inferred to be abortive, or transformed flower- 179 180 ISl 183 Thorns. 179, Cratajgus parvifolia (thorns axillary.) 180, Iloney-locnst. ISl, Common locust 182, Borboris, a, a, its thorns. 316. Spines. Many plants arc armed, as if for self-defense, with hard, sharp-pointed, woody processes, called spines or thorns. Those which are properly called spines originate from loaves. In Berberis the spines are evidently transformed lea\'cs, as the same plant exhibits leaves in every stage of tho metaraorpiiosis. In goat's-lhorn (Astraga- lus tragacanthiis) of S. Europe, the petioles 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. 31'if. Thorns originate from axillary buds, and are abortive branches. This is evident from their position in the hawthorn and Osage orange. Tho ajiple and pear tree in their wild state produce thorns, but by cultivation become thornless that is, the axillary buds, through better tillage, develop branches instead of thorns. The terrible branching thorns of the honey-locust originate just above the axil, from accessory buds. 318. Prickles differ from either spines or thorns, growing from tho epidermis upon stems or leaves, at no determinate point, and consisting of hardened cellular tissue, as in the
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