NERVES OF LEAVES. 31 



of the nerves, and both are constituted of the same fibres and 

 vessels. It must not be supposed from the names that have been 

 arbitrarily given them, that these parts are similar in function to 

 those parts of animals of the same name. 



18. Sometimes the leaf presents one or more primary nerves 

 which diverge in a straight line from the base of the blade, and 

 give rise to more slender nerves, that separate from each other, 

 following a straight line, and forming an angle with the first 

 (Jig. 28) : at other times the principal nerves are curved from 

 their base (fi,g. 34). 



19. We give the name of angu'linerve leaves to those in 

 which the primary and secondary nerves are straight, and form 

 angles with each other (Jig. 26), and we call those curvinerve 

 leaves in which the primary nerves are curved (figs. 37 and 43). 

 The first belong chiefly to ex'ogenous or dicotyle'donous plants, 

 and the second to endogenous or monocotyle'donous plants. 

 (Monocotyle'donous. From the Greek, monos, single, and kotu- 

 ledon, seed-lobe. Applied to plants that have but one seed-lobe 

 or cotyledon in the embryo.) 



20. The angu'linerve leaves present four principal arrange- 

 ments ; sometimes they are penninerve; that is, provided with a 

 middle nerve (called also midrib), which is a prolongation of the 

 petiole, and which gives off to the right and left secondary 

 nerves, like the feathers of a pen (for example, the olive leaf, 

 Jig. 22, the leaf of the yoke-elm, and of the beech tree) ; some- 

 times they are palminerve^ that is, provided with several primary 

 nerves which separate from each other at the base of the blade, 

 like the divisions of a fan (Jig. 28) ; for example, the leaf of the 

 grape vine, which has five primary nerves, and that of the mal- 

 lows, in which we count seven or even nine : the number of 

 these nerves is always unequal, and that of the middle appears 

 to be the prolongation of the petiole ; peltinerve (fig. 45), that is, 

 provided with nerves that radiate on an oblique plane relatively 

 to the petiole, so as to constitute a sort of disk or shield, placed 

 upon its peduncle (foot), (for example, the leaf of the nastur- 

 tium) ; and in others again they are pedalinerve, that is, having 

 a very short central nerve or midrib, from which spring two 

 largely developed lateral nerves, the ramifications of which are 

 very small towards the external side (edge) of the leaf and very 



1 8. Are the nerves of all leaves alike in arrangement ? 



19. What are anguli nerve leaves ? 



20. What is a penninerve leaf? (Penninerve, from the Latin, penna, pen 

 or feather.) What is a palminerve leaf? (Palminerve, from the Latin, 

 palma, palm of the hand.) What is a peltinerve leaf? (Peltinerve, from 

 the Latin, pelta, a shield.) 



