38 THE STORY OF THE PLANTS. 



with transparent walls, and no colouring matter 

 (Fig. 1). These cells are full of water ; they 

 form a sort of water-cushion on the top of the 

 leaf, which drinks in carbonic acid (or, to be 

 quite correct, its floating form, carbon dioxide) 

 from the air about it. Immediately below this 

 cushion of water-cells you come again upon a 



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FIG. 1. A THIN SLICE FBOM A LEAF, SEEN UNDER 



THE MICROSCOPE. On top are water-cells, which 

 suck in carbonic acid. Beneath these are 

 green cells, which assimilate it under the 

 influence of sunlight. The spongy lower 

 portion is used for evaporation. 



firm layer of closely-packed green cells, filled with 

 living green- stuff, which take the carbonic acid 

 in turn from the water-cells, and manufacture 

 it forthwith into sugars, starches, and other 

 materials of living bodies. The lowest spongy 

 part evaporates unnecessary water, and so helps 

 to keep U_cirgulation, 



