1919] CRIBBS—TILIA AMERICANA 285 



advances, the growth water in the spring being higher than at 

 any other time. 



12. The amount of growth water in the soil apparently has 

 very little influence on the transpiration index, unless it is reduced 

 to the wilting coefficient. It might be argued that a low growth 

 water is the cause of the saturation deficit depression, but there 

 is evidence that it is due rather to the inability of the translocating 

 system to conduct water to the leaves with sufficient rapidity to 

 offset the transpiration loss, and not to a slowing up of the absorp- 

 tion rate. This is substantiated by the occurrence of the typical 

 deficit in readings on Tilia when the growth water was greater 

 than 20 per cent. The drop that occurs when the soil moisture 

 falls to the wilting coefficient is more permanent and is due to 

 stomatal movement which accompanies visible wilting. 



I wish to express my grateful appreciation of the encourage- 

 ment and suggestions given by Dr. Geo. D. Fuller, of the 

 University of Chicago. 



College of Emporia 

 . Emporia, Kan. 



LITERATURE CITED 



1. Bakke, a. L., Studies on the transpiring power of plants as indicated by 

 the method of standardized hygrometric paper. Jour. Ecol. 2:145-173. 

 1914. 



2. Briggs, L. J., and Shantz, H. L., Daily transpiration during the normal 

 growth period and its correlation with the weather. Jour. Agric. Res. 

 7:155-212. 1916. 



3. , The wilting coefficient and its indirect determination. Bot. 



Gaz. 53:20-37. 191 2. 



4. Briggs, L. J., and McLane, L. W., The moisture equivalent of soils. 

 U.S. Dept. Agric. Bur. Soil Bull. 45. 1907. 



5. Fuller, G. D., Evaporation and soil moisture in relation to the succes- 

 sion of plant associations. Box. Gaz. 58:193-234. 1914. 



6. Livingston, B. E., Light intensity and transpiration. Box. Gaz. 52: 

 417-438. 1911. 



7. , Atmometry and the porous cup atmometer. Plant World 18: 



21-30, 51-74, 95-iii» 143-149- 1915- 



8. , The resistance offered by leaves to transpirational water loss. 



Plant World 16:1-35. 1913. 



