A Study of Leaves 



47 



wind. It has a firm vein running around the margin which 

 prevents tearing. The thin broad leaves of a Banana have no 

 such border. The wind would bring such a strain on the trees 

 that they would be blown down were it not that the leaves tear 

 down between the veins. The younger leaves are rolled, so 

 that less surface is exposed to the wind. The Date Palm de- 

 fends itself in the same way, only the leaf splits earlier and has 

 a more tidy appearance. It looks like a compound leaf when it 



Fig. 53. — Firmly bound leaf of Senecio sp. 



is quite unfolded. Examine young date leaves. They are 

 plaited instead of rolled. 



When leaves are branched, the branching depends upon 

 the branching of the veins. In some leaves there is a strong 

 central vein, from which other veins branch on either side as 

 the pinnae branch from the quill of a feather. Such venation 

 is termed pinnate. Or several strong veins may start from 

 the base or lower portion of the leaf, and the venation is said 

 to be palmate (hand-like). 



In most dicotyledons the prominent veins join each other 

 so as to form an irregular network ; the veinlets end freely and 



