130 CLARK— ON WATER CONTENT 



Results show (1st) that there is no connection between water content 

 and transpiration, temperature, and relative humidity; (2nd) that from 

 8 A. M. to 5 p. M. there is practically no variation in water content, but 

 that variations are regular and constant for transpiration; (3rd) average 

 water content was greater for Hamamelis virginiana, than for Fagus 

 americana and Quercus alba; (4th) average transpiration was greatest 

 for Fagus americana and least for Quercus alba; (5th) water content is 

 highest in the Spring, lowers during the Summer, and rises again in the 

 Fall; (6th) transpiration is greatest in the Spring and lowest in the Fall. 



A general conclusion of results may be stated as follows: 



1) Under the same conditions, water content and transpiration 

 differ in different species. 



2) Water content is independent of transpiration, temperature, and 

 relative humidity. 



3) Water content is constant from 8 a. m. to 5 p. m. Large supply 

 of soil-moisture may be an influential factor here. 



4) Water content varies during seasonal changes. This may be 

 accounted for by structural differences in the leaves from the stages of 

 early development, to those of senility. 



VII. Acknowledgments 

 Great pleasure is taken in expressing to Dr. H. A. Gleason of the 

 University of Michigan, my appreciation of his able and helpful gui- 

 dance while engaged in the preliminary experiments at the University 

 Biological Station. To Dr. John W. Harshberger of the University of 

 Pennsylvania I owe greatest thanks for his generous and profitable 

 assistance along various lines of the present problem. For construc- 

 tion of simple apparatus and for valuable suggestions I feel deeply 

 indebted to Dr. Enoch Karrer of the Physical Laboratory of the United 

 Gas Improvement Company of Philadelphia. To Mr. and Mrs. WilUam 

 H. Clark of Lenape, Pa. I wish to express my gratitude for the privileges 

 and hospitality of their Brandywine farm during the experimental 

 phases of the subject. My appreciation is also extended to Miss Mabel 

 M. Thackara of the Commercial Course of the Germantown High School, 

 whose valuable manipulation in clerical details has brought the present 

 work to its close. 



Philadelphia, Pa. April 6, 1916. 



