150. Three sorts of pinnate leaves are here given. Fig. [156] is pinnate with an odd or end leaflet, as in the Common Locust and the Ash. Fig. [157] is pinnate with a tendril at the end, in place of the odd leaflet, as in the Vetches and the Pea. Fig. [158] is evenly or abruptly pinnate, as in the Honey-Locust.
Fig. 159. Palmate (or digitate) leaf of five leaflets, of the Sweet Buckeye.
151. Palmate (also named Digitate) leaves are those in which the leaflets are all borne on the tip of the leaf-stalk, as in the Lupine, the Common Clover, the Virginia Creeper (Fig. [93]), and the Horse-chestnut and Buckeye (Fig. [159]). They evidently answer to the radiate-veined or palmately-veined simple leaf. That is, the Clover-leaf of three leaflets is the same as a palmately three-ribbed leaf cut into three separate leaflets. And such a simple five-lobed leaf as that of the Sugar Maple, if more cut, so as to separate the parts, would produce a palmate leaf of five leaflets, like that of the Horse-chestnut or Buckeye.
152. Either sort of compound leaf may have any number of leaflets; yet palmate leaves cannot well have a great many, since they are all crowded together on the end of the main leaf-stalk. Some Lupines have nine or eleven; the Horse-chestnut has seven, the Sweet Buckeye more commonly five, the Clover three. A pinnate leaf often has only seven or five leaflets, or only three, as in Beans of the genus Phaseolus, etc.; in some rarer cases only two; in the Orange and Lemon and also in the common Barberry there is only one! The joint at the place where the leaflet is united with the petiole distinguishes this last case from a simple leaf. In other species of these genera the lateral leaflets also are present.
153. The leaflets of a compound leaf may be either entire (as in Fig. [126]-[128]), or serrate, or lobed, cleft, parted, etc.; in fact, may present all the variations of simple leaves, and the same terms equally apply to them.
154. When the division is carried so far as to separate what would be one leaflet into two, three, or several, the leaf becomes doubly or twice compound, either pinnately or palmately, as the case may be. For example, while the clustered leaves of the Honey-Locust are simply pinnate, that is, once pinnate, those on new shoots are bipinnate, or twice pinnate, as in Fig. [160]. When these leaflets are again divided in the same way, the leaf becomes thrice pinnate, or tripinnate, as in many Acacias. The first divisions are called Pinnæ; the others, Pinnules; and the last, or little blades themselves, Leaflets.
