THE LEAVES. 



125 



145). More profound branching is evident in divided or 

 parted leaves (fig. 146). In 

 some blades the branching 

 is so extensive and complete 



B 



Fig. 145. Fig. 146. 



Fig. 145. — Diagrams of slight leaf branching. A, leaf with crenate edge ; B, leaf with 



dentate edge ; C, leaf with serrate edge. — After Bessey. 

 Fig. 146. — Leaf of Amorphophallus, showing sympodial branching. The successive 

 lateral axes are numbered in order. The extent of branching makes the blade divided. 

 Reduced. — After Sachs. 



that the green tissue no longer fills the intervals between the 

 larger ribs, but the blade is made up of a series of independ- 

 ent portions united to a common stalk. Each ultimate 

 branch of the blade is known as a leaflet. Blades in which 

 the green tissue is continuous, even though deeply divided, 

 are called simple leaves. (See figs. 136, 138, 141, 142, 145, 

 146.) Those which are segmented into leaflets are called 

 compound 'leaves. (See figs. 139, 144, 147, 148, 149.) 



156. Venation. — The mode of branching of the blade is 

 indicated by the main ribs which occupy the axes of growth. 

 (See % 169.) Study of distribution of the ribs and veins of 

 the blade, that is, of its venation or nervation, shows that 

 monopodial branching (^[ 93) is the common mode, sympo- 

 dial branching occurring rarely (fig. 146). The arrangement 

 of the larger ribs may be reduced to two main types.* (1) 



* Compare mode of branching of shoot, \ 103. 



