no GLIMPSES INTO PLAXT-LIFE 



surface, and placed so evenly parallel to each other 

 that they have been compared to the pales of a 

 fence, and are called palisade tissue. These cells 

 contain a quantity of the green substance called 

 chlorophyllon (from chloros, green, and phyllon, a 

 leaf), so named because to this bright green sub- 

 stance we owe all the lovely verdure of our woods 

 and gardens. 



Below this palisade tissue is another of quite a 

 different form, consisting of large spongy cells, and 

 therefore known as spongy tissue. 



In its intercellular spaces are stored those 

 secretions which make certain herbs, such as 

 thyme, marjoram, and others so fragrant when 

 bruised. 



The chemical changes which are ever going on 

 in these various layers, require a constant supply 

 of the outer air, and this is secured by the little 

 openings, called stomata, on the under surface of 

 the leaf, which have been already described ; these 

 constitute the breathing apparatus of the leaf, for 

 they open and shut, and regulate the supply of 

 air into little air chambers, from which it passes 

 into the structure (^i the plant. 



