OF LEA VE8 IN GENERAL. 



147 



194.— Leaves, like other members of the plant-body, may 

 braiKih during their growth. At first they are always simple, 

 and if the growth is uniform the result is a simple leaf ; if, 

 however, as frequently happens, the growth is more rapid at 

 certain points, branches may arise, as in the so-called com- 

 pound leaves. All grada- 

 tions are observable between 

 simple leaves, in which the 

 growth has been absolutely 

 uniform (producing entire 

 margins), to compound 

 leaves with jointed leaflets. 

 The differentiation is here 

 much like that which takes 



place in passing from the ^ig-l^S.-Three-lobedleaf of Hepatica. 



thallome to the form of plant-body with distinct caulome 

 and phyllome. 



The simplest cases are those in which the branches are 

 rudimentary, as in the serrate (Fig. 1^4, A), dentate (Fig. 

 124, B), crenate (Fig. 134, 0), and other similar forms. 

 When the branches are more prominent they give rise to 

 lobes of various kinds (Figs. 125, 126). "Where the longitu- 

 dinal growth of the leaf (not of its 

 branches) is but little, the lobes ap- 

 pear to radiate from a common 

 point, as in hepatica, mallow, maple, 

 etc. ; such are called radiately, pal- 

 niately, or digitately lobed. Where, 

 as in the oak, the longitudinal 

 growth of the leaf is considerable, 

 the lobes are laterally arranged upon 

 a central portion ; such leaves are 

 said to he pinnately lobed. 

 195. — Leaf -branches frequently become so developed that 

 they themselves form distinct leaves, and thus we have what 

 is termed the compound leaf (Figs. 127 and 128). Terms 

 similar to those used in the case of lobed leaves are here 

 used also ; thus where the secondary leaves (leaflets) grow 

 from an extremely short axis, so that they radiate fjrom a 



three-lobed sag- 

 ittate leaf. 5, three-lobed has- 

 tate leaf. 



