STRUCTURE OF LEAVES. 71 

 STRUCTURE OF LEAVES. 



1. In most leaves the blade has, runn in-- 

 through it, a number of veins, often conspic- 

 uous, especially on the lower side, as rid. 

 The leaf of the hibiscus shows them very 

 plainly, and, on holding such a leaf to the light, 

 it is seen that there is a perfect network 

 of these veins, the small veins being branches 

 of the larger ones. These veins are really the 

 continuations of the woody tissue which we 

 have already seen in the stem and are of use 

 as a supporting framework to the soft tissue 

 of the leaf, spreading it out to the light and 

 air and preventing the leaf being readily torn. 

 They are also the means whereby the water 

 taken up by the roots is brought to the leaf, 

 and the substances manufactured in the leaf 

 are carried away to the other parts of the 

 plant. 



2. The veins of leaves are arranged in 

 two main ways : netted, as in the hibiscus : 

 parallel, as in the banana and all grasses, where 

 the veins run side by side and do not form an 

 interlacing network. These two types of vein 

 arrangement netted and parallel are, on the 

 whole, characteristic of the leaves of dicoty- 

 ledons and monocotyledons respectively, and 

 with certain exceptions, for instance the yam, 



