TRANSPIRATION. 



153 



called stomata (Fig. 41). They are formed by two 

 cells, called guardian cells, with a narrow slit be- 

 tween them, which they have the power to open 



FIG. 41. 



I. Stomata on a Leaf of Peperomia arifolia. 2. Cross-Section of the Same Leaf. 

 (" Pflanzenleben.") 



or to close. Both the cells are shaped like a half- 

 moon, with the concave side towards the slit and 

 the convex side joining the neighboring cells of 

 the epidermis. Beneath the opening of each stoma 



