GENERAL MORPHOLOGY OF THE PLANT 77 



is by no means uncommon. In aquatic plants, again, where 

 some of the leaves are submerged, while others float on the 

 water, or rise above it into the air, as in the Water Crowfoot 

 {Ranunculus aquatilis) and Arrowhead (Sagittaria sagitti- 

 folia), the leaves thus differently situated frequently vary in 

 shape. 



5. Form. — By this term we understand the solid configura- 

 tion of the lamina. The terms used in defining the various 

 forms are therefore especially applicable to thick or succulent 

 leaves. Such leaves either assume some regular geometrical 

 forms, as cylindrical, pyramidal, conical, prismatic, &c., and 

 receive corresponding names ; or they approach in form to some 

 well-known objects, and are hence termed acicular, ensiform, 

 &c. Various other singular forms are also found, some of which 

 will be hereafter alluded to. 



Besides the above-described modifications which the blades 

 of leaves present in reference to their Margins, Incision, Apex, 

 Outline, and Form, they also present numerous other variations 

 as regards their surface, texture, colour, &c. 



Compound Leaves. 



We have already defined a compound leaf. Its separate leaf- 

 lets are subject to the same modifications of their margins, in- 

 cision, apex, outline, form, texture, surface, colour, &c., as the 

 blades of simple leaves, and the same terms are accordingly 

 used in describing them. We have therefore only now to 

 speak of compound leaves as a whole, and the terms which 

 are employed in describing their special modifications. We 

 divide them into two types : the Pinnate and the Palmate or 

 Digitate. 



1. Pinnate Compound Leaves. — When a leaf of this type 

 presents the appearance of several distinct portions or leaflets, 

 it is termed pinnate {figs. 93, 94, 150) ; and the leaflets are 

 then termed pinnce. The leaflets are arranged in an opposite 

 manner along the sides of the rachis or primary axis in 

 pairs, and according to their number the leaf is said to be one-, 

 two-, three-, or, many-paired. Several kinds of pinnate leaves 

 have also been distinguished by special names. Thus, when 

 the main axis of a pinnate leaf is only winged at the extreme 

 apex, thus appearing to bear a terminal leaflet {fig. 93), as in the 

 Rose and Elder, it is imparipinnate or unequally pinnate, 

 or pinnate with am odd leaflet ; it is equally or abruptly 



