18 



ELEMENTS OF BOTANY. 



lei or slightly divorgont course toward the margin or apex (Fig. 15). Such 

 leaves are teriued parallei'veined ; and here is found cue of the disthic- 

 tious between endogenous and exogenous plants. 



In exogenous plants the venation is extremely varied and gives rise to 

 many different forms. In oufl particuhir, however, there is uniformity : 



FlO. 26.— Slrtipln, pinnately voincrt loaf of chestnut. Margin Rcrrnto. 



the ultimate ramifications of the veins produce a net-work ; hence such 

 leaves are termed net-veined, and are thereby distinguished from the 

 parallel-veined leaves of endogenous plants. 



One of the commonest forms of exogenous leaves is that in which the 

 mid-^-ein pursues a direct coarse from the base to the apex, giving off, at 

 regi:lar intervals, lateral branches which extend parallel with each other 

 to the margin. Such leaves are denominated pinnately or feather- 

 veined. The leaves of the beech and chestnut (Fig. 2G) are familiar ex- 

 amples of this form. 





Via. 27.— Simple, palmatcly veined leaf of castor-oil plant {Bicinus comviunis). 



Another common form of net-veined leaves is that in which there is no 

 stron ^ly marked mid-vein, but instead a number of large veins pursue a 

 diverj^ent course from the base to the margin of the leaf. There may be 

 thrc ;, four, seven, or nine of these veins, diverging like the fi-ngers of an 



