Volume 10 Number 12 



The Plant World 



DECEMBER, 1907 



EVAPORATION AND PLANT DEVELOPMENT.* 



By Dr. Burton Edward Livingston. 



By far the greater portion of the water absorbed by 

 growing plants merely makes up for the loss occasioned by 

 transpiration. This water is absorbed by the root system, 

 transmitted through the conducting tissues, and escapes into 

 the air whenever moist cell walls are exposed. The daily 

 water loss from any individual plant at any stage of its 

 growth is largely determined by the evaporating power of 

 the air. At any given time in the development of the plant, 

 and under the corresponding conditions of soil moisture, 

 there is a maximum rate of water supply to the transpiring 

 tissues, and when the evaporating power of the air is so 

 great as to cause the rate of loss to surpass that of supply, 

 the plant wilts and is injured or killed, unless, indeed, it is 

 provided with water storage organs, which may temporarily 

 free it from dependence upon external supply. In ordinary 

 plants a quiescent existence can be maintained when the rate 

 of transpiration approaches or equals that of supply, but un- 

 der these conditions v^ery little or no growth can take place. 



The evaporating power of the air depends upon three 

 factors, humidity, temperature, and wind velocity. Although 

 numerous attempts have been made to derive a formula for 



*This Mrticie is n.ainly abstracted from a paper presented at the 

 meetin?r of tlie Iloriiciiltural Society of New York, October 1, 1907, which will 

 be publisneii in 'he Proceedings of the Society. 



