48 



STUDIES IN PHYSIOLOGY 



(see Fig. 14) we can make out a multitude of minute rec- 

 tangular objects, the leaf cells, each being surrounded by a 

 thin wall of woody material. Within each cell-wall there are 

 numerous minute green masses known as chlo'ro-phyll bodies 

 (from Greek, meaning leaf green). These chlorophyll bodies 

 are grains of the cell protoplasm, having a peculiar green 

 substance, by the help of which they are enabled to carry 

 on the manufacture of starch in the presence of sunlight. 



Starch Manufacture. For the manufacture of starch, the 

 raw materials, carbon, hydrogen, and oxygen, must be fur- 

 nished to these chlorophyll bodies. The water (H 2 0) that 



epidermis covering upper surface 

 of the leaf. 



leaf cells containing green chlo- 

 rophyll bodies. 



epidermis covering lower surface 



of the leaf, 

 stoma (one of the openings through the epidermis into the 



interior of the leaf). 

 FIG. 14. Cross section of a leaf very much magnified. 



comes up from the roots supplies the necessary amount of 

 hydrogen and oxygen. The carbon is obtained from the 

 carbon dioxid found in the air. The latter passes into the 

 leaf through the outer layer of cells by means of many 

 little openings or mouths known as sto'ma-ta (Greek sto- 

 mata = mouths). In some unknown way the chlorophyll 

 bodies, when acted upon by sunlight, are able to separate 

 the carbon dioxid into oxygen and carbon and to cause the 

 carbon thus obtained to unite with the hydrogen and oxygen * 



1 The whole process may be represented by a formula something as 

 follows : 



