7 ARMATURE. PART I. 



a strong and rigid process issuing from the stem or 

 branch, in which case it originates in the wood 

 (PI. I. Fig. 6.), or from the foot-stalk or expansion 

 of the leaf, in which case it originates in the marginal 

 or other nerves. The branches of the Sloe and 

 Hawthorn afford examples of the former, and the 

 leaves of the Holly-tree, Robinia Pseudacacia, and 

 Aloe afford examples of the latter. The foot-stalks 

 of Astragalus Tragacantha, and the stipulae of 

 Xanthium spinosum and the Mimosa, which are 

 persistent, are finally, when indurated by age, con- 

 verted into real thorns.* 



Terminal In some plants the thorn is terminal, as in Riam- 

 nus catharticus ; in some it is lateral, as in- the 

 Hawthorn ; in some it is simple and solitary, as in 

 Celastrus buxifolius ; in some it is forked or divided, 

 as in Ardidna bispinosa (PL III. Fig. 13.); and in 

 others it grows in sets of two, thee, or more together, 

 as in Gleditsia. 



j i. It has been observed by Linnaeus and others 

 that the thorn will sometimes disappear in conse- 

 quence of cultivation. Thus Pyrus sativa, which in 

 its wild state is furnished with strong thorns, is, in 

 its cultivated state, found to be wholly without 

 them. But this peculiarity is incidental only to the 

 thorn, and does not affect the other species of arma- 

 ture, neither of which shows any tendency to dis- 

 appear in consequence of cultivation. From the 

 effects of culture upon the thorn in is liability to 

 * Smith's Introduction, p. 224. 



tlOD. 



