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BOTANY: PRINCIPLES AND PROBLEMS 



its leaf-area, its transpiration-rate, and the moisture and fertility 

 of the soil. Of most significance to the plant, however, is not the 

 actual bulk of transpiration, but the efficiency with which the 

 water is used. This is determined by comparing the weight of 



Fig. 39. — The water-requirement of a corn plant. The amount of water 

 transpired from this corn plant, during its growth and development, would under 

 normal conditions fill the barrel. 



the total water transpired with the weight of the dry plant 

 material ultimately produced, their quotient being known 

 as the water-requirement of the plant. Thus when we say that 

 the water-requirement of corn under certain conditions is 400, we 

 mean that for every gram of dry weight of corn plant produced 



