70 JOHN W. SHIVE AND WILLIAM H. MARTIN 



ploys the horn hygroscopeof Darwin,^ the other the hygrometric 

 paper of Stahl.^'' It is the latter method as improved by Living- 

 ston and Shreve,ii which has been employed in the present study. 



It was the purpose of the experiments here recorded to meas- 

 ure, at different hours of the day, by means of standardized 

 cobalt chloride paper, the transpiring power of leaves which 

 had previously been covered with a film of Bordeaux mixture, 

 and to compare the values thus obtained with those derived 

 from similar measurements made at the same hours upon un- 

 treated leaves of the same plant and of different plants. It was 

 thought that such a comparison might give some indication of 

 the relative rates of water loss from treated and untreated 

 plants grown under agricultural conditions, a consideration 

 of some importance in connection with the study of crop pro- 

 ductions in general. The experiments further served as a 

 practical field test of an improved method of cobalt chloride 

 paper when applied to studies involving the effect of surface 

 films on the loss of moisture from plant surfaces; studies which 

 heretofore have been confined almost wholly to detached plant 

 parts or to potted plants grown under artificial conditions. 



It is a pleasure to acknowledge indebtedness to Dr. Byron 

 D. Halsted for his kind consent to the use of a field plot on the 

 experiment grounds of the Department of Botany of the New 

 Jersey Agricultural Experiment Station, where the field tests 

 were carried out. 



METHODS 



The method employed for the tests with cobalt chloride paper 

 is essentially the one described by Livingston and recently 

 improved by Livingston and Shreve, as already stated. The 

 improved method makes use of composite paper slips consist- 



8 Darwin, F., Observations on stomata. Phil. Trans. Roy. See. Lend., B. 

 190: 531-621. 1898. 



1° Stahl, E., Einige Versuche tiber Transpiration und Assimilation. Bot. 

 Zeit. 52: 117-146. 1894. 



11 Livingston, B. E. and Shreve, Edith B. Improvements in the method for 

 determining the transpiring power of plant surfaces by hygrometric paper. Plant 

 World 19: 287-309. 1916. 



