io6 GLIMPSES IXTO PLAXTIJFE 



buds are so placed that each leaf shall receive 

 its full share of sunH<^ht and air, for it needs this 

 position in order to enable it to carr)- out the 

 wonderful work of assimilation which it has to 

 perform. 



The upper surface of a leaf is covered b)- a thin 

 layer of cells, known as the epidermis (or skin) ; 

 this does not prevent the light from falling 

 through, and its outer surface is protected by a 

 thickening, known as the cuticle. This is of great 

 use in controlling the escape of moisture, other- 

 wise the leaf would soon shrivel up in a hot sun. 

 In a young seedling leaf the cuticle is not de- 

 veloped, and it can therefore breathe out moisture 

 very rapidly ; later on, when the cuticle is formed, 

 it controls the escape of moisture, which can then 

 only exude through the under surface of the leaf. 



We can easily peel off a portion of the skin 

 from the under surface of the leaf, and if we place 

 it in a little water between two pieces of glass 

 and look at it in a microscope we shall see that 

 it consists of an extremely thin la}'er of cells, 

 with numbers of little openings called stomata 

 (from the Greek stoma, a mouth), answering 



