Leaves. 



8 9 



cells, and so give over to them the water that they bring 

 from the roots, and receive from them the products of their 

 manufacture. Thus we see that the leaf is in reality a 

 factory to which the raw materials are constantly 



FIG. 37. 



the essential working parts of a leaf and their relation to each 

 -> r ! the upper epidermis containing one stoma ; S, a sieve tube 

 '! manufactured materials are removed from the leaf; r, a tra- 

 cheal tub-*, tr./f>ugh which water is brought into the leaf; between these tubes 

 iis four palisade cells are shown with chloroplasts (rounded, 

 m bedded iiTthe cytoplasm lining their walls. The downward- 

 pointing irrov ; indicate the light energy which penetrates to and is absorbed by 

 the chloroplasis. The gas interchange of photosynthesis and transpiration is 

 indicated by fie curved arrows. 



brought, and from which the finished product is as con- 

 stantly being tr? . ported. //* 



67. Method of the Leaf's Work. The plan of the leaf 

 and the method of its work will be still better understood 

 by reference to the diagram of Fig. 37. For the sake of 

 simplicity, only a few palisade cells covered by a small 

 portion of the epidermis, and a sieve tube and water tube, 



