06 THE LEAF. PART I. 



Fig. 11.), which exhibit a singularity of structure 

 unparalleled, as it appears, in the natural history of 

 leaves. 



The expansion, like the petiole, is generally dis* 

 tinguishable into an upper and under surface, of 

 which the upper surface is generally flat or rather 

 somewhat concave, and the under surface slightly 

 convex, or perhaps even keeled by the longitudinal 

 ridge of the midrib. The former is also more 

 smooth than the latter, and of a deeper shade of 

 green, as may be very distinctly perceived in the 

 leaves of the Bramble and White Poplar. If the 

 ramifications of the midrib are large and conspicuous, 

 the leaf is said to be ribbed, as in the leaf of Water 

 Plantain. (PL II. Fig. 12.) If the surface is much 

 raised between the smaller divisions of the nerves, 

 the leaf is said to be wrinkled, as in Scotch- 

 kale ; and if the surface is moulded into a number 

 of overlapping folds, the leaf is said to be plaited, 

 as in the beautiful leaf of Ladies' Mantle. (PL II. 

 Fig. 13.) 



.leave* If the leaf springs immediately from the root, it 

 te h r fzed" is sai d to be radical; if from the origin of the 

 from their branches, it is axillary; if from the extremity of the 



insertion. 



branches, it is terminal. If it surrounds the stem 

 or branch by its base, it is called an embracing leaf; 

 and if it enfolds and invests the stem by its base, 

 it is called a sheathing leaf, as in the Grasses. 

 And clis- The leaves, like the branches, are in their dis- 

 tribution, opposite, or alternate, or tufted, or 



