VOLUME LVIII 



NUMBER 6 



THE 



Botanical Gazette 



DECEMBER ig 14 



THE TRANSPIRATION OF EMERSED WATER PLANTS: 



ITS MEASUREMENT AND ITS RELATIONSHIPS 1 



Charles Herbert Otis 



(with three figures and fourteen charts) 



Introduction 



The evaporation taking place from free water surfaces has been 

 the subject of much experimentation during the past century, and 

 the laws governing this phenomenon have been quite definitely 

 stated. The matter of transpiration of plants, a special kind of 

 water evaporation, has also been the subject of a great deal of 

 theoretical and experimental investigation, and we know the 

 quantity of water transpired by certain plants in various situations 



of the factors which influence it. But, although the 



some 



1m 



water supply, especially where immense irrigation and water 

 supply projects are involved, practically no investigation of any 



mine 



from 



It has been a matter of common belief that emersed water 

 plants transpire large amounts of water, although there seems to be 



little evidence in support of such belief. Fanning (6) says, "Marshy 

 margins of ponds are profligate dispensers of vapor to the atmos- 

 phere, usually exceeding in this respect the water surfaces them- 

 selves." Such statements as this, unsupported by experimental 



1 Contribution no. 143 from the Botanical Department of the University oi 

 Michigan. 



457 



