48 PRACTICAL BOTANY. 



97, The Surface of the blade of a leaf is said to be 

 undulate, or wavy, if bent up and down ; crisjy, when bent 

 irregularly np and down ; rugose, wrinkled ; ])licate, or 

 folded, gathered into longitudinal folds ; 7iervosey or nerv- 

 ed, with strong vascular bundles, nerves, or ribs ; veined, 

 having thin and slender vascular bundles, especially 

 branching ones, veins. "We distinguish netted^eined (PI. 

 II., 12) and jparallel^eined leaves (PI. II., 10), and other 

 sorts of venation, which will be considered presently in 

 connection with certain divisions of the margin. 



98. The division of the margin of leaves witH refer- 

 ence to the framework of their surface. 



Leaves are, as regards the principal bundles of their 

 w^oody fibres, either feather-veined {jyinnately-veined) or 

 radiate-reined (the same ii's> palmatcly-veined). 



The first-named sort has only one longitudinal rib or 

 nerve, extending from the top of the petiole to the apex 

 of the leaf, and this rib, also called the midrib, sends out 

 branches, or veins, which are divided into branchlets or 

 veinlets. Sometimes the two lowest branches of the mid- 

 lib are very strong and long, and the leaf is then called 

 trijyle-ribbed or triple-nerved. 



The other sort has three to five or more ribs or nerves, 

 instead of a single one ; hence we distinguish three-ribbed 

 (triple-nerved), five-inbbed, seven-ribbed, etc., leaves. 



]^ow, according to these two modes of venation, we 

 distinguish two modes of division into segments, calling 

 some leayes, pijinateli/- and others palmatelf/- cleft, parted, 

 or divided. (See PI. II., 3-6.) A few modifications of 

 pinnately-cleft or parted leaves are designated by particular 

 terms. Pectinate we call pinnately-parted leaves, with 

 very close and narrow divisions, resembling the teeth of a 

 comb ; lyrate, or lyre-shaped, those with the segments de- 



