86 THE GARDEN OF EARTH 



leaf, is the blade, the wide green portion. This reminds 

 one of an oar, the chief part of which is called " the 

 blade." 



A leaf, like all the rest of a plant, is formed of countless 

 tiny cells, pressed and growing together ; and the mass 

 of these, green in colour, is known as the " cellular 

 tissue " of a leaf. This word " tissue " means strictly 

 " that which is woven " ; and here it stands for the 

 kind of substance which may become part of a living 

 body, either of plant or of animal. 



The ribs and veins of a leaf — ^its skeleton — are also 

 formed of cells; but these cells have hardened into a 

 tough substance, which is fit to act as a strong frame- 

 work for the soft tissue. And over the whole is a fine 

 transparent skin or cuticle, both above and below, through 

 which the green tint can be clearly seen. 



In this skin are numbers and numbers of extremely 

 minute openings; tiny pores or holes, so formed that 

 they can open or close according to the needs of the 

 plant. They are indeed so tiny that they cannot be 

 seen at all without a powerful microscope. If you were 

 to prick a hole in paper, with the point of the very 

 finest needle, that hole would be simply huge side by 

 side with a single leaf-pore. 



By far the greater number of them are on the under- 

 sides of leaves. No doubt this is because the under- 

 side is the more sheltered, and not nearly so much 

 exposed as the upper-side to rain and wind and dust. 

 And each of them is the doorway to a minute channel or 

 passage, leading to and from the inside of the leaf. 



No one would guess how great is the number of these 



