Leaves. 



89 



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 being 



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

 other. Z, portion of the upper epidermis containing one stoma ; 6", a sieve tube 

 through which the manufactured materials are removed from the leaf; r, a tra- 

 cheal tube through which water is brought into the leaf; between these tubes 

 and the epidermis four palisade cells are shown with chloroplasts (rounded, 

 shaded bodies) embedded in the cytoplasm lining their walls. The downward- 

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

 the chloroplasts. The gas interchange of photosynthesis and transpiration is 

 indicated by the curved arrows. 



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

 stantly being transported. 



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. 



