250 VEGETABLE ORGANOGRAPHY. 



One of the remarkable cases among penninerved 

 leaves is, that where the two lower nerves, although 

 evidently springing from the middle one, are larger 

 than all the following, and almost attain the size of those 

 of the middle, these leaves are called Triplinerved ; 

 for example, Helianthus tuherosus. Sometimes the two 

 lower nerves of each side are large, and near each other, 

 and then the leaf is Quintuplinerved (for example, 

 in several species of Melastoma), because it has five 

 nerves near the base, viz, — two on each side, springing 

 from the middle one. 



This structure leads us by almost imperceptible de- 

 grees, to the second of the great classes of leaves. 



2d. Leaves are said to be Palminerved {i. e. having 

 the nerves disposed like the fingers, separate from each 

 other), when several diverging nerves spring at the same 

 time from the base of the limb : they are most frequently 

 of an uneven number, the middle one being prolonged 

 direct from the petiole. Sometimes as many as seven 

 or nine nerves are counted; for example, in several 

 Malvaceas — Malva Hennigii, M, Braziliensis^ Sec, Al- 

 thcea, &c. &c. Most frequently only five are found, as 

 in the Vine ; or three, as in the Zizyphus, and a number 

 of other plants ; but it is often difficult to distinguish 

 accurately between quinquinerved and trinerved palmate 

 leaves, and quintuplinerved or triplinerved ones. The 

 only difference consists, in fact, in this — that in the 

 latter the fibres remain a little longer connected with 

 the central bundle, or the parenchyma is prolonged a 

 little along the summit of the petioles. Equal numbers 

 of nerves are much rarer than in the preceding, and 

 probably are only owing to combinations of leaves, 

 originally impari-pinnate. We can, at least as to the 

 appearance, reckon among palminerved leaves with 

 equal numbers of nerves, those of Bauhinia, where there 



