FOLIAGE AND SCALE LEAVES. 



59 



Via. 22.— Pinnately 

 lobed Leaf of Oak. 



in which the margin is more deeply excavated. Projections, 

 whether small, as teeth, or large, as lobes, generally correspond to 

 smaller or larger veins. Lobes 

 and the like which follow the 

 latter are therefore arranged 

 either pinnately or palmately. 

 A distinction is drawn between 

 lobed, deft, and parted leaves, 

 where the excavations extend, 

 respectively, not more than 

 half way, half way or more, 

 and almost the whole way to 

 the midrib or base. In the 

 first case, either the lobes or in- 

 terspaces are rounded, and in 

 the second, sharply cut. Thus 

 we get pinnately and pcdmaiely 

 lobed, cleft, and parted leaves 

 (figs. 22 and 23). The lobes 

 may be of very unequal size 

 and shape (as in potato), their 

 margins varying like those of 

 complete leaves. Secondary lobes 

 rases, and still smaller subdivisions may also occur. Examine in 

 this connection the thrice pinnately-parted leaves of the yarrow 

 or millefoil. 



In a large number of leaves division actually extends to the 

 midrib or base, giving pinnately or palmately-divided forms. The 

 lobes are then termed leaflets, and the leaves are corn-pound, as 

 opposed to simple leaves, such as those described up to this point. 

 Leaflets may be either sessile or stalked, and their general out- 

 line. Arc, are described in the same terms as simple leaves. Pin- 

 nately and palmately-divided compound leaves are termed pinnate 

 oy palmate. Examples of the former condition are seen in elder, 

 ash, and rose (ef. rig. 24). The axis upon which the leaflets are 

 borne clearly answers to the midrib of a simple leaf, and cases 

 are not infrequent in which the end of a pinnate leaf is not 

 completely divided. This may be seen very well in the jessamine. 

 The strawberry (fig. 25) and horse-chestnut (fig. 26) furnish 

 typical instances of palmate leaves, where the leaflets are attached 

 together at the tip of the petiole. Leaflets, like leaves, are often 

 attached by means of a joint or articulation, where separation 

 readily takes place. This enables us to distinguish between pin- 

 nate and palmate leaves with only three leaflets. Compare these 

 structures, for example, in scarlet runner (fig. 29) and clover. 



Fig. r:.— Pinnately- 

 cleft Leaf of Poppy. 



are thus produced in many 



