WATER OF SOIL IN ITS RELATION TO PLANTS 247 



169. Factors affecting transpiration. — These figures 

 serve to indicate not only the variation between crops, 

 but also the great effect of climate and soil on transpira- 

 tion. 1 The factors may be listed under three heads, as 

 follows : — 



1 A complete review of the literature concerning the climatic 

 and soil factors in their effect on transpiration may be found 

 as follows : Briggs, L. J., and Shantz, H. L. The Water 

 Requirement of Plants. U. S. D. A., Bur. Plant Ind., Bui. 

 285. 1913. 



by transpiration. In later experiments covers were used in 

 order to cut down evaporation. 



4 King, F. H. Physics of Agriculture, p. 139. Published 

 by author, Madison, Wisconsin, 1910. Also, The Number of 

 Inches of Water Required for a Ton of Dry Matter in Wis- 

 consin. Wisconsin Agr. Exp. Sta., 11th Ann. Rept., pp. 240- 

 248. 1894 ; and The Importance of the Right Amount and 

 Right Distribution of Water in Crop Production. Wisconsin 

 Agr. Exp. Sta., 14th Ann. Rept., pp. 217-231. 1897. 



King used cans holding about 400 pounds of soil. Some were 

 set down into the earth while others were not. Part of the 

 work was carried on in the field; the remainder was run in 

 vegetative houses. Normal soils were used. Evaporation 

 from soil was very low, water being added from beneath. The 

 data quoted are the average of a large number of tests. 



5 Leather, J. W. Water Requirements of Crops in India. 

 Memoirs, Dept. Agr., India, Chem. Series, Vol. I, No. 8, pp. 

 133-184, 1910, and No. 10, pp. 205-281. 1911. 



Jars containing from 12 to 48 kilograms of soil were used. 

 Loss by evaporation was determined on bare pots. The plants 

 were grown in culture houses or in screened inclosures. 



6 Briggs, L. J., and Shantz, H. L. Relative Water Require- 

 ment of Plants. U. S. D. A., Jour. Agr. Research, Vol. Ill, 

 No. 1, pp. 1-63. 1914. Also, The Water Requirements of 

 Plants. U. S. D. A., Bur. Plant Ind., Bui. 284. 1913. 



Plants were grown in cans holding 250 pounds of soil. Evap- 

 oration from soil was prevented by means of a paraffin covering. 

 Work was conducted in screened inclosures. The data are the 

 average of several years' work. 



