THE LEA VES. 



12S 



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 ; /.', leaf ^^th 



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

 Fig. 146. — Leaf of A lUOT/'hopkalhiS, ■iWiw'Wi^ sympodial branching. The successi\'e 

 lateral axes are numbered in order. Tlte e.xtent of branching makes the blade di\ided. 

 Reduced. — After Sachs. 



that the green tissue no longer fills the inter\"als 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 \\hich 

 the green tissue is continuous, even though deeplv divided, 

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

 146.) Those "which are segmented into leaflets are called 

 compound \ea\iis. (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 gro"ivth. 

 (See •[ 169.) Studv of distribution of the ribs and veins of 

 the blade, that is, of its vena/ion or nervalio?!, shows that 

 monopodial branching (•j' 93) is the comn"ion mode, sympo- 

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

 of the larger ribs ma}- be reduced to two main types.* (i) 



* Compare mode of branching of shoot, 



