^52 VEGETABLE ORGANOGRAPHY. 



the appearance of a disc placed upon the summit of it ; 

 it is this appearance, which, compared to a shield, has 

 caused these leaves to be called peltinerved : such are 

 those of the Ricinus communis, Trop(Eolum majus, &c. 

 When all the nerves which radiate from the top of the 

 petiole are equal in length, the leaf has nearly an orbi- 

 cular form, and the angle of the limb with the petiole is 

 almost a right one ; when the angle is acute, the nerve, 

 which, by its direction, is the prolongation of the petiole, 

 lengthens more than the others, which, on both sides, 

 diminish in length : the general form then is ovate, or 

 even sometimes elongated. There are cases where the 

 narrow part of the limb is so much contracted that pel- 

 tate leaves are confounded with palmate ones ; and 

 species are found among the Menispermeae, for example, 

 the leaves of which assum.e almost indifferently these 

 two forms. Thus all that I have said of palmate leaves 

 may be applied to those which are only a modification. 



4th. Pedalinerved leaves differ much from all the 

 preceding, in that the longitudinal nerve remains very 

 short, sometimes nearly absent ; but from both sides of 

 it arise two strong lateral ones, which diverge upon the 

 same plane, and, instead of ramifying equally on the 

 two sides, present few or no lateral nerves on the outer 

 side, whilst on the inner they give rise to very strong 

 secondary ones, nearly parallel to each other. This 

 singular disposition only exists in a small number of 

 plants ; and notwithstanding this circumstance, it is 

 remarkable that these are the leaves where the distinc- 

 tion between angulinerved and curvinerved ones, or 

 those of Dicotyledons and Monocotyledons is least de- 

 cided. Among the first, pedalinerved leaves are found 

 in the Gincko, Hellehorus fcetidus, and some species of 

 Passiflora ; among the second, several are found in the 

 Aroideae ; these have, it is true, a very decided tendency 



