LEAVES. 



25 



up its orifice, as in Sarracenia 100 and Nepenthes 104 , it is called 

 a pitcher or ascidium ; if it is unclosed, and is a mere sac, as 

 in Utricularia, it is called ampulla 101 . 



202. Sometimes the petiole has no lamina, or is lengthened 

 beyond the lamina, and retains its usual cylindrical or taper 

 figure, but becomes long, and twists spirally ; such a petiole 

 is called a fewrfriJ (Vrille, Fr.). 



The petiole is usually either taper, or channelled ; and it has often a struma" 1 , 

 (coussinet, Fr.) at either its base or apex, especially in those leaves which 

 are sensitive. In other cases it is inflated 106 , sheathing 103 , ainplexicaul 107 , 

 winged 108 , auriculate, leafless, jointed 108 , spinescent ' 10 , &c. 



203. The petiole is sometimes articulated transversely as in 

 the Orange. 



204. The LAMIXA of a leaf is an expansion of the- paren- 

 chyma of the petiole, and is traversed by veins which are rami- 

 fications or extensions of the bundles of vascular tissue of the 

 petiole, or, when there is no petiole, of the stem. 



205. Sometimes one, sometimes both the surfaces of a 

 leaf are furnished with stomates. 



206. The veins either branch in various directions among 

 the parenchyma, anastomosing and forming a kind of net- 

 work, or they run parallel to each other, being connected by 

 single transverse uubranched veins. 



207. The former is characteristic of Exogenous, the latter 

 of Endogenous plants. 



