. 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 Off THE liBAr. 314. The petiole of the leap of Clematis, otherwise unchanged, 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. 315. But THE TENDEILS OF THE GEAPE-viNE are of'a different nature. Prom their position opposite the leaves, and the tubercles occasional
. 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 Off THE liBAr. 314. The petiole of the leap of Clematis, otherwise unchanged, 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. 315. But THE TENDEILS OF THE GEAPE-viNE are of'a different nature. Prom 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,. 179 180 181 Thorns. 1T9, Cratffigus parfifolla (thorns axillary.) 180, 181, Common looost 182. Borberis, a, a, its thorns. 316. Spines. Many plants are armed, as if for self-defense, with hard, sharp-pointed, woody processes, called spines or thorns. Those which are properly called spines originate from leaves. In Berberis the spines are evidently transformed leaves, as the same plant exhibits leaves in every stage of the metamorphosis. In goat's-thorn (Astraga- lus tragacanthus) of S. Europe, the petioles change to spines after the leaflets fall off. In the locust (Kobinia), there is a pair of spines at the base of the petiole, in place of stipules. 31f. Thorns originate from axillary buds, 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 thomless, 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 the epidermis upon stems or leaves, at no determinate point, and consisting of hardened cellular tissue, as in the rose, bramb
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