T WOODS AND FIELDS 187 



the parenchyme run " fibre- vascular bundles," 

 forming a sort of skeleton to the leaf, and 

 comprising air-vessels on the upper side, rayed 

 or dotted vessels with woody fibre below, and 

 vessels of various kinds. The under surface 

 of the leaf is formed by another layer of 

 flattened cells, supporting generally more or 

 less hairs, and some of them specially modi- 

 fied so as to leave minute openings or 

 " stomata " leading into the air passages. 

 These stomata are so small that there are 

 millions on a single leaf, and on plants growing 

 in dry countries, such as the Evergreen Oak, 

 Oleander, etc., they are sunk in pits, and fur- 

 ther protected by tufts of hair. 



The cells of the leaf again are themselves 

 complex. They consist of a cell wall per- 

 forated by extremely minute orifices, of pro- 

 toplasm, cell fluid, and numerous granules 

 of " Chlorophyll," which give the leaf its 

 green colour. 



While these are, stated very briefly, the 

 essential parts of a leaf, the details differ in 

 every species, while in the same species and 

 even in the same plant, the leaves present 



