104 



OUTLINES OF PLANT LIFE. 



intervals between the larger ribs, but the blade is made up 

 of a series of independent 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 



B 



Fig. g6. Fig. 97. 



Fig. g6. — Diagrams ot slight leaf branching. .<4 , leaf with crenate edge ; 5, leaf with 



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

 Fig. 97 —Leaf of Amorpko/i/iallus, s^xovrmg sympodial branching. The successive 

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

 Reduced. - After Sachs. 



called jzw/i/e leaves. (See figs. 87, 89, 92, 96, 97.) Those 

 which are branched into distinct leaflets are called compound 

 leaves. (See figs. 90, 95.) 



129. Venation. — The ribs and veins, being composed in 

 part of the vascular strands which enter the leaf, and in part 

 of stiffening mechanical tissues, branch profusely and in such 

 a way that no part of the green tissue is far from a vein. In 

 figures 98 and 99, though none of the finest branches are 

 shown, some idea of the complete distribution of the veins 

 may be obtained. 



The branching of the ribs and veins agrees in the main with the differ- 

 ent modes described for the shoot, ^ 89, which see. A formal account of 

 venation may be found in Gray's Structural Botany, pp. 90-94. 



130. Special forms, — Foliage leaves may be modified to 

 serve special purposes without wholly losing their function 



