CH. VIl] 



VEINS. 



101 



the edge of the leaf, branching and becoming smaller till 

 the smallest branchlets are only visible to the naked eye 

 by holding the leaf against the light.j 



The veins are the ramifications of the vascular bundles 

 and therefore contain xylem- vessels. Vessels, it must be 

 remembered, are the water-carriers of the plant, and 

 when it is considered how easily a leaf withers, or in 

 other words how great is its need of water, the fine 

 ramification of the water pipes is opt surprising. The 

 leaf may be compared to a country cut up into innumer- 

 able minute fields by an elaborate system of irrigation. 



Fio. 46. 



TRANSVERSE SECTION THROUGH THE LEAF OF THE HELLEBORE, 

 showing, from above downwards, the upper epidermis, the palisade 

 cells, the spongy tissue (in which a vascular bundle is seen), the 

 lower epidermis, in which is shown a single stoma opening into a 

 large intercellular space. 



It must be remembered that the veins not only serve 

 for irrigation but also supply a framework for the support of 



