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 



Fig. 146. 

 ) , leaf with crenate edge ; />', leaf with 



ARC 

 Fig. 145- 

 Fig. 145.— Diagrams of slight leaf branching 



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

 Fit;. 146. — Leaf of A morphophallus, showing sympodial branching. Th 

 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 leases. (See figs. 136, 138, 141, 142, 145, 

 146. ) Those which are segmented into leaflets are called 

 compound leaves. (See figs. 139, 144, 147, 148, 141).) 



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

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

 (See ^1 169.) Study of distribution of the ribs and veins of 

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

 monopodial branching (*T 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, " i".;. 



