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TEXTBOOK OF PLANT PHYSIOLOGY 



coating with vaseline the lower surface of such leaves which have 

 no stomata on the upper side, leaves of many trees are best for this 

 purpose. These leaves will continue to transpire, although at a 

 reduced rate. This loss of water through the cuticle is called 

 "cuticular transpiration," as distinguished from "stomatal trans- 

 piration" in which water escapes through the stomata. In fully 

 developed leaves stomatal transpiration is 10 to 20 times as rapid 



Fig. 69. — Graphs showing the daily march of transpiration and the most 

 important factors determining it {according to Briggs and Shantz). 



as cuticular transpiration. But in young leaves, with cuticle, not 

 completely developed, as well as in leaves growing in the shade or 

 in a moist atmosphere, half of the water may be transpired through 

 the cuticle. Moistening of the leaves also increases considerably 

 cuticular transpiration, as was mentioned in Art. 47. 



Stomatal transpiration consists of two phases : the evaporation 

 from the surface of the water-saturated mesophyll cells lining the 



