THE FOOD OF THE PLANT 



29 



In some plants, which grow in dry situations where 

 little water is available, no transpiration at all is pos- 

 sible from the upper surface of the leaves. On the 

 other hand when leaves present both surfaces equally 

 to the sun, transpiration takes place equally from both 

 sides. 



When looked at with the naked eye a leaf appears to 

 be covered by a complete skin, and it is difficult to see 



A, privet leaf, lower surface. C, maize leaf, lower surface. 



B, ,, upper surface. D, „ upper surface, 

 c, cell. !f, stoma. A, hair. £r, guard-cell, o, opening. 



Fig. 13 



how transpiration can be effected at all. If, however, 

 a piece of this " skin" is examined under a microscope 

 it is seen to be made up of a number of tiny parts re- 

 sembling somewhat the cells of a honeycomb (Fig. 13), 

 and for this reason termed "cells" by the botanist. 

 Scattered among the cells are little pores (s), and it is 

 through these pores that the water-vapour escapes. 

 They are called "stomata" or "mouths." Sometimes 

 the stomata are to be found on both .surfaces of the 



