26 SYLVA AMERICANA. 



pruned away by the skilful planter and horticulturist. They 

 have a rough bark, and produce only a few blackish buds. 



Of Th orn s. 



Thorns are stunted branches ; their imperfect form may be 

 owing to the buds being partially evolved, from want of proper 

 nutrition. Indeed, that it is, in a great degree, owing to such a 

 cause, is proved by the conversion of thorns into branches on 

 removal into richer soil. This fact is well known to gardeners, 

 as many fruit trees, which are thorny when wild, become smooth 

 when cultivated. Some times the foot-stalks of pinnate leaves 

 that have fallen off become thorns, as in the case in the 

 Astragalus tragacantha, or goat's thorn milk vetch. 



Of Prickles. 



Prickles may be taken off with the bark, and is therefore a 

 mere elongation of that organ, which is chiefly composed of 

 cellular substance, and of cortical vessels. There is this 

 remarkable distinction between the prickle and the thorn, that 

 no cultivation whatever can convert the former into a shoot, as 

 is the case with the latter ; for the vessels become very rapidly 

 hard, separate from the stem, and at last is merely retained by 

 the exterior covering. The stipules of some plants are converted 

 into prickles, as in Berberis vulgaris, or common berberry. 



Of the Flo wer stalk and Footstalk. 



The flower stalk and foot stalk are also composed of cellular 

 texture, of central and cortical vessels, which convey the 

 vegetable juices to and from the leaf. 



Of the Tendrils. 



Tendrils have the same structure as the preceding, and are in 

 fact elongated foot stalks, without the leafy expansion, which 



