SECT. I. ORGANOGBAPHY AND GLOSSOLOGY. 



71 



any dicotyledonous plant where the petioles are 

 " sheathing." 



(78.) Spines. Some leaves, which do not freely 

 develop in the usual manner, assume a dry hardened 

 appearance, and pass into spines, as in the common 

 furze; just as some abortive branches have been stated 

 to assume the character of thorns (art 62.). In the 

 berberry (fig. 68.) all the intermediate states (#) be- 



tween a well-developed leaf and the hard spine, may 

 be distinctly traced, on vigorous suckers of a year's 

 growth. 



(79-) Tendril. In some leaves, the midrib is pro- 

 truded beyond the apex of the limb, in the form of a 

 filamentous chord, and, in many cases, the limb entirely 

 disappears, and the whole petiole is transformed into 

 what is termed a " tendril." These organs serve to 

 support the weak stems of certain plants, by twisting 

 round the branches of others, in their neighbourhood. 

 F 4 



