510 CONSERVATIVE ORGANS. [LECT. IX. 



Veined (venosum), expresses merely that 'the 

 fasciculi of vessels are so elevated or marked in 

 their branching and sub-branching, as to form a 

 kind of network over one or both surfaces of the 

 leaf. When the 'surface is altogether free from 

 any appearances of the vascular fasciculi, the 

 leaves are said to be nerveless, or veinless (enervia, 

 aveniaj, 70. 



In speaking of the substance of a leaf, as far 

 as that can be determined from its external cha- 

 racters, we refer to the expansion only ; for, al- 

 though the substance of the petiole is often the 

 same as the expansion, yet this state is neither con- 

 stant nor essential. All leaves may be regarded as 

 herbaceous; but the term is occasionally employed 

 in a determinate sense to denote a soft, green, 

 pliable leaf, the vascular fasciculi of which 

 are as succulent, and scarcely firmer than the 

 rest of the leaf; as exemplified in Spinage, Spi- 

 nacia dleracea, the different species of Goose-foot, 

 Chenopodeum, &c. A leaf is termed membra- 

 nous (membranaceum) , when it is thin and pliable, 

 the quantity of parenchymatous matter being so 

 small that the cuticle of the one surface appears 

 almost closely applied to the other; as in Broad- 

 leaved Birthwort, Aristolochia sipho; Scented 

 Bramble, Rubus odoratus ; and most trees and 

 shrubs : but this term does not imply that uni- 

 formity of substance which the ^ appellation herba- 



