Page:An introduction to physiological and systematical botany (1st edition).djvu/254

 224 The permanent footstalks of the Gum Tragacanth shrub, Astragalus Tragacantha, are hardened into real Spines, as are the flowerstalks in Pisonia, as well as the stipulas of Xanthium spinosum and the Mimosæ.—''Linn. Mss.''

4. Aculeus, a Prickle, arises from the bark only, and comes off with it, having no connection with the wood, as in Rosa, Rubus (the Bramble Raspberry, &c.), and Zizyphus, ''Willd. Sp. Pl. v.'' 1. 1102.

This is not liable to disappear by culture, being very distinct in nature from the last.

5. Cirrus. A Tendril. This is indeed properly called a fulcrum or support, being intended solely to sustain weak and climbing stems upon more firm and sturdy ones. By its means such climbers often reach, in tropical forests, to the summits of lofty trees, which they crown with adventitious blossoms. Tendrils or claspers when young are usually put forth in a straight direction; but they presently become spiral,