60 LEAVES. 
198. When the fibres are clustered together for a little 
way phelore they expand, they constitute what is called a pe- 
tiole or footstalk, as in the Horse-chestnut (Aisculus hippo- 
castanum), and trees. See ‘Fig. 9, the leaf of Black Bryony 
(Tamus communis). 
199. The leaf is therefore said to consist of two partayad 
the leaf-stalk or petiole, and the leafy expansion, called i 
lamina or dise, the part usually termed the leaf. 
200. The petiole is formed of spiral vessels, woody tissue, 
- and cellular tissue, and resembles the stem and braaches i 
structure. 
201. In some cases, as in the simple leaves of the NV 
_se of New Holland, the lamina is not developed, and the pe- 
tiole becomes expanded, or leafy, in which case it is called 
phyllodium. It is termed a pitcher or ascidium, when it’ 
expanded into a cup or hollow vessel at its. extremity, as in 
. Nepenthes distillatoria or pitcher plant. 
202. The projecting lines seen on the under te 
the leaf, and called veins or nerves, are the ramifications 
the vascular and woody tissue which proceed from — 
‘stem. 
203. Most leaves are divided into two lateral halves b 
a3 large vein extending from the base to the summit. This 
a continuation of the petiole, and is called the midrib. 
its base and sides the other veins proceed and spread in all 
< directions. See Frontispiece, Fig. 4, the leaf of the Com- 
mon Primrose. One side, however, is occasionally larger 
_ than the other, or of a slightly different form, as in wap 
: —- lime tree (Tilia Europea). 
: _ 204. baenarses of most exogenous or oophetonous 
te 
