6o 



BOTANY. 



Function of the leaf 

 in transpiration. 



The living protoplasm retards the evaporation of 

 water somewhat from the cells. 



The water escapes from the cells of the middle part 

 of the leaf into the intercellular spaces. From 

 here it passes out through the openings (sto- 

 mates). 



When transpiration is in excess of root pressure, 

 the guard cells close together and shut the open- 

 ing, and thus greatly retard the loss of water. 



The cuticle, a thin deposit on the outer surface of 

 the epidermal cells, also retards more or less 

 transpiration. 



Material. — Fresh leaves of some plant like begonia, ivy, or other leaf 

 which is easy to section. Where preferred, permanently mounted slides of 

 sections of leaves may be used. 



