TRANSPIRATION FROM PLANTS 175 



Of one thing we are fairly sure; if the upward stream 

 of water is wholly stopped for even a few hours, the 

 plant is likely to be so severely inj ured as to be greatly 

 handicapi^ed in its future growth. 



Botanical authorities agree that transpiration is 

 of value to plant growth, first, because it helps to dis- 

 tribute the mineral nutrients necessary for plant 

 growth uniformly throughout the plant; secondly, 

 because it permits an active assimilation of the car- 

 bon by the leaves ; thirdly, because it is not unlikely 

 that the heat required to evaporate water, in large 

 part taken from the plant itself, prevents the plant 

 from being overheated. This last mentioned value of 

 transpiration is especially important in dry-farm 

 districts, where, during the summer, the heat is often 

 intense. Fourthly, transpiration apparently influ- 

 ences plant growth and development in a number of 

 wavs not yet clearly understood. 



Conditions influencing transpiration 



In general, the conditions that determine the 

 evaporation of water from the leaves are the same 

 as those that favor the direct evaporation of water 

 from soils, although there seems to be something in 

 the life process of the plant, a physiological factor, 

 which permits or prevents the ordinary water-dis- 

 sipating factors from exercising their full powers. 

 That the evaporation of water from the soil or from 



