THE LEAVES OF VASCULAR PLANTS. 24-9 



to form the limb, after two different principles: 1st. 

 Some separate by forming, either with the base or with 

 its prolongation, an angle, properly so called, and most 

 frequently a right angle ; we may call these An gu li- 

 ner ved leaves ; 2d. The others separate by forming at 

 the base, or its prolongation, a curve more or less 

 extended: these may be named, by comparison, Cur- 

 viNERVED leaves. The former are essentially the leaves 

 of Dicotyledons ; the latter, the true limbs of those of 

 Monocotyledons. 



Among angulinerved leaves, 1 have for a long time 

 distinguished four dispositions of the nerves ; viz. — 



1st. Penninerved leaves (Pi. 10, fig. 3), or those in 

 which the petiole is prolonged into a longitudinal nerve, 

 which emits, from both sides, upon the same plane, late- 

 ral nerves ; for example, the Chestnut. These lateral 

 nerves are sometimes thick, at others very slender ; 

 sometimes far apart, at others near one another ; some- 

 times simple, at others more or less ramified ; sometimes 

 perfectly straight, at others curved at their extremity, 

 gradually following the border of the leaf, &c. They 

 form at their origin, with the longitudinal nerve, an 

 angle, usually acute, but the degree of which varies 

 much. In certain leaves the angle is very acute, and 

 the leaf is generally elongated. At other times they 

 separate at a much less acute, or even at a right angle, 

 and then the leaf is proportionally larger. Another 

 difference influences much the form of penninerved 

 leaves, viz. — the relative proportion of the lateral nerves. 

 If the leaf has all of them short, but of the same lensrth, 

 its form is Linear ; if those of the middle are lonsrer 

 than those of the base and apex, the form is generally 

 Elliptic, Oval, or Orbicular ; if the longest are 

 found below the middle, the limb is Ovate ; if they are 

 above it, it is Obovate. 



