LEAVES, THEIR FORM AND MOVEMENT 8 1 



the divisions extend deeper the leaf is cut, when nearly or 

 quite halfway to the midrib the leaf is lobed, when halfway or 

 more cleft, when nearly to the midrib parted, and when the divi- 

 sions extend quite to the midrib the leaf is divided. The margins 

 of the lobes or divisions may then be plane or serrate, etc. These 

 divisions take place between the more prominent veins so that the 

 leaf may be pinnately lobed, parted, divided, etc., or palmately 

 lobed, etc., according to the kind of venation. 



127. Compound leaves. Compound leaves are those leaves 

 in which the divisions of the blade are complete and regular and 

 the divisions are set off distinctly from each other somewhat like 

 distinct leaves, or leaflets. 



B C 



Fig. 71. 



A. Rose leaf, pinnately compound, odd pinnate, hairy stipules. B. Leaf of pea, pinnately 

 compound, terminal leaflets replaced by tendrils, leaf-like stipules. C. Clover leaf, palmately 

 compound, persistent stipules. 



128. Significance of leaf division. The leaves are impor- 

 tant organs for certain kinds of work for the plant. Within certain 

 limits the work of the leaf is in proportion to its spread of surface. 

 Beyond certain limits of spread, however, thin leaves are in danger 

 of injury, since they would be whipped about more by the wind. 

 Divisions of large leaves permit the currents of air to pass with 

 6 



