I08 THE VEGETATIVE FUNCTIONS OF PLANTS 
110. Stomata and Gaseous Exchange. In Chapter IV 
we described the openings or stomata in the epidermis of 
leaves, through which water-vapor passed to the out- 
side. We also learned in Chapter VII that the inter- 
change of gases in photosynthesis takes place through the 
stomata. So, also, does the exchange of gases that 
FIG. 70. White birch (Betula populifolia). Portion of a branch showing 
the prominent lenticels. 
accompanies respiration. As the oxygen within the 
cells is consumed in respiration, more is absorbed from the 
intercellular spaces. Thus its pressure becomes less 
within the leaf than without, and consequently oxygen 
enters by diffusion through the stomata. At the same 
time the air in the intercellular spaces becomes richer 
