128 STRUCTURAL BOTANY. [109,110. 



326. But the tendrils of the Grape vine 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 trans- 

 formed flower-stalks. 



327. 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 evi- 

 dently transformed leaves, as the same plant exhibits 



402 403 



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

 beris a, a, its thorns. 



leaves in every stage of the metamorphosis. In Goafs- 

 thorn (Astragalus tragacanthus) of S. Europe, the pet- 

 ioles 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 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 

 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. Prickles differ from either spines or 

 thorns, growing from the epidermis upon stems of leaves, at no determinate 

 point, and consisting of hardened cellular tissues, as in the Rose, Bramble. 



