

STUDIES IN EVAPORATION AND TRANSPIRATION 1 



Geo. F. Freeman 



(with FIVE figures) 



As the result of studies extending over several years, consider- 

 able experimental data have been accumulated concerning the 

 transpiration of alfalfa and other plants under various accurately 

 measured conditions of temperature, relative humidity, and wind 

 movement. It was found, however, that the interpretation of 

 these results was hopeless unless something more was known 

 about the quantitative influence of these factors upon purely physical 

 evaporation than was available to the writer. Thus it was impos- 

 sible to say whether a given result was simply the product of the 

 physical factors then obtaining, or to what extent it was modified 

 by the physiological reactions of the plant itself. One should be 

 able to calculate from rational formulae the behavior of a physical 

 evaporating surface for the given conditions. Any departure from 



this result could then be attributed to the response of the living 

 organism. 



It may be assumed that the general type of such a formula will 

 remain the same for all situations, but that the constants will vary 

 with all of the varying conditions of environment, temperature, 

 wind movement, relative humidity, and size and nature of the 

 evaporating surface. The purely physical experiments here 

 reported were designed, first to work out the generalized type of 

 the formula, and then to obtain the constants for certain special 

 cases of environment and other factors. Environment is used 

 here in a restricted sense, meaning only the size and nature of the 

 space within which the evaporating surface is inclosed. In the 

 work reported this was one liter of space included within a glass 

 cylinder closed by two large rubber stoppers at either end. 



When 



ixperiments 



Experiment Station during the writer's connection with that institution, which 

 extended over the years 1909-1918. They were, for the most part, conducted during 

 the latter part of this period. 



Botanical Gazette, vol. 70] 



[190 



