TRANSPIRATION AND LEAF-WATER 9 



piece 2. Pieces 2 and 3, however show a rise in transpiration and 

 in this behave like the radio-atmometer. Between these hours, 

 namely from 10 to 12, lies, for the day of observation, the period 

 of maximum net loss of water, and this would, under a clear sky, 

 doubtless be extended from 9 to 13, unless some behavior in the 

 plant should enter in to reduce the evaporation from the leaf. 

 That such a factor may intervene is suggested by the various 

 behavior of the pieces during the 12-13 hour. That stomatal 

 movement is not the determining factor seems to be excluded by 

 the data on stomatal behavior in hand. That conditions within 

 the leaf may work to this end is quite probable, among which 

 that of the cell walls under a relatively low vapor tension within 

 the intercellular spaces is probably very important. 6 



From the thirteenth hour on till about sunset the two rates 

 are nearly the same, but, while there is some vacillation, there is a 

 pretty constant though very small net loss of water. Something 

 must be allowed for error, but scarcely more than 0.05 cc. The 

 size and distribution of the ratios compel the conclusion, there- 

 fore, that the amount of water in the plant fluctuates from hour 

 to hour. Eberdt 7 came to a similar conclusion, finding corre- 

 sponding day and night fluctuations in Helianthus annuus, from 

 which the inference was drawn that the water-loss through the 

 foliage and the intake through the roots are two different things, 

 but no light is thrown on the seat of low tension. One may sup- 

 pose the fluctuation to be either in the stem (involving negative 

 pressure as ordinarily conceived) or in the leaves, or in both. As 

 the leaves in the experiments being considered did not betray any 



6 Livingston, B. E. Relation of the Daily March of Transpiration to Varia- 

 tions in the Water Content of Foliage Leaves. Bot. Gaz. In press. For a 

 sharply analytical study of the relation of water in leaf and stem, see Renner, O., 

 Experimentelle Beitrage zur Kenntnis der Wasserbewegung. Flora, 103: 171-247. 

 1911. That, under the conditions of the experiments described in the present 

 paper, the fluctuations in water-content are probably referable very largely, if 

 not entirely, to the leaf is supported by Renner' s experiments on the influence of 

 the length of the stem on the absorption of water by the leaf (Renner, I. c. 

 p. 204). Renner also finds evidence, obtained by other methods, for concluding 

 that "in transpirierenden Blattern besteht also immer ein Sattigungsdefizif 

 (I. c, p. 243). . 



7 Through Burgerstein. A. Die Transpiration der Pflanzen. Jena. 1904, p. 17. 



