152 



GREEN PLANTS AS FOOD MAKERS 



outgrowths from the petiole at its base. In many leaves the 

 stipules fall off early. Some leaves are compound, that is, each of 



parallel 

 veinect 



How do these leaves differ ? In what ways are they alike ? 



the little leaflike parts or leaflets is in reality a section of the leaf 

 blade which is so deeply indented that it is cut away to the midrib 

 or central vein, as in the rose leaf shown in the figure below. 



The cell structure of a leaf. The 

 outer covering of a leaf, on both the 

 upper and the lower surfaces, is 

 called the epidermis, and is com- 

 posed of large, irregular cells. The 

 under surface of a leaf seen through 

 a microscope usually shows many 

 tiny oval openings, called stomata 

 (sto'md-td, sing, sto'ma). Two cells, 

 kidney-shaped, are found, one on 

 each side of a stoma. These are the 

 guard cells. By a change in the 

 shape and size of these cells, due to 

 absorption of water, the stoma is 

 made larger or smaller. 

 Study of the leaf in cross section 



f*stipules 



recc clover y rose 



How pan you tell that these are com- 

 pound leaves? 



