100 MORPHOLOGY OF LEAVES. 



muUifid, &c. Fig. 162, a leaf of Dragon Arum, is palmately 

 ^-parted. But, as the lateral sinuses are not so deep as the 

 others, the leaf is said to be pedately parted, or pedate, in the 

 early terminology. 



191. Moreover, as the lobes or divisions of a leaf may be 

 again similarly lobed or parted, &c., this composition may be 

 indicated by the prefix twice, thrice, &c., as twice pinnatifid or 

 Upinnatijid, thrice pinnately parted, thrice palmately parted, and 

 the like. Thus, a word or two, or a short phrase, may describe 

 even a complex leaf, so as to convey a perfectly clear and defi- 

 nite idea of its conformation. 



192. A distinction should now be drawn between simple and 

 compound leaves. The distinction cannot be both natural and 

 absolute ; for the one may pass variously into the other. Simple 

 leaves, which have been thus far considered, have a single lamina 

 or blade, which may, however, at one extreme be entire, at the 

 other many-parted, and even several times divided. 



193. Compound Leaves are those which have from two to 

 many distinct blades, on a common leafstalk. These blades, 

 called LEAFLETS, may be sessile on the common leafstalk, or they 

 may have leafstalks of their own. As the leaf very commonly 

 separates in age by an articulation of its petiole with the stem, 

 so leaflets are commonly more or less articulated with the com- 

 mon petiole. When the leaf, with its petiole, falls from the 

 stem, the leaflets may as completely separate from the common 

 petiole. They do not always do this. Divided leaves, such as 

 those of Fig. 198 and 202, though ranked among the simple 

 sorts, are compound in the sense of having distinct blades, 

 but without articulation. Some of these blades are apt to be 

 confluent ; that is, a divided leaf is often in part merely parted, 

 as in the upper portion of Fig. 198. Such leaves are so inter- 

 mediate between simple and compound that it becomes indiffer- 

 ent, or a matter of convenience to be settled by analogy, under 

 which head or by what language they shall be described. How- 

 ever, most leaves are so constituted as to leave no doubt whether 

 they are simple or compound. 



194. The leaflets of a compound leaf being homologous with 

 the lobes or segments of a simple leaf, indeed being such segments 

 fully isolated, the two sorts fall under the same types. A pin- 

 nately veined simple leaf is the homologue of one kind of com- 

 pound leaf; a radiately veined leaf, of the other. That is, 

 compound leaves are either pinnate or palmate. 



195. Pinnate Leaves (Fig. 203-205) are those in which the 

 leaflets are arranged along the sides of a petiole, or rather of its 



