458 BOTANICAL GAZETTE [December 



evidence, are of only passing interest, yet they constitute all of 

 the scanty literature on the subject. 



This investigation was undertaken to secure experimental data 

 leading to a better knowledge of the quantity of water transpired 

 by emersed water plants, its relationships, and some of the factors 

 which influence it. 



Relation between the amount of water transpired and the 



amount of water absorbed by the roots 



Woodward (13) in the latter part of the seventeenth century 

 measured the amount of water absorbed by the roots, and con- 

 sidered this amount to be a measure of the quantity transpired. 

 Bessey and Woods (i), in criticism of this method, pointed out that 

 such observations are misleading, that the amount of water ab- 

 sorbed is not necessarily proportional to the amount transpired. 

 Two years later, criticizing a similar mode of reasoning by 



Schneider (10), Woods (12) says, "first of all he has made a very 

 great mistake in assuming that the amount of water absorbed by 

 the roots of a plant represents the amount transpired," and quotes 

 in support of his argument the investigations of Eberdt, Burger- 





stein, Vines, and Goodale. Woods also points out that tran- 

 spiration is not something which protoplasm does but something 

 which it resists. It is not a physiological function or activity of 

 protoplasm, although it may have a physiological relation to the 

 normal development of certain plants or parts of plants. Tran- 

 spiration is nothing more than evaporation." 



Burgerstein (2) reports that Vesque, using a 0.35 per cent 

 nutritive solution in which bean plants were grown for a period of 

 56 days, found a water intake of 92.65 gm. and a water outgo of 

 82 . 105 gm. He cites also the work of Krober with leafy branches 

 of Asclepias incarnata, and shows by the results given in table I 

 that the amount of water taken up by the cut surfaces differs 

 from the amount given off by transpiration, 



Ewart and Rees (5), working with trees, make the statement 

 that "The rate of evaporation per sq. m. of leaf surface from cut 

 branches, whether placed in water or not, is always less than from 

 a plant rooted in the soil, under otherwise similar conditions." 



