THE RELATION OF ATMOSPHERIC EVAPORATING 

 POWER TO SOIL MOISTURE CONTENT AT PER- 

 MANENT WILTING IN PLANTS.! 



JOHN W. SHIVE AND BURTON E. LIVINGSTON 



The Johns Hopkins University, Baltimore, Md. 



INTRODUCTION 



It is now generally recognized that the moisture residue re- 

 maining in the soil at the time when plants growing therein 

 become permanently wilted varies greatly according to the 

 nature of the soil, this moisture content being higher in the case 

 of soils having a greater water holding capacity and lower in 

 the case of soils with less power of retaining water. It is only 

 in comparatively recent years, however, that detailed attention 

 has been given to the relations of atmospheric conditions to 

 this soil moisture residue and to the phenomenon of wilting itself. 

 In the earlier literature dealing with the relation of plants to 

 soil moisture, atmospheric conditions, if considered at all, were 

 described only in the most general way, and adequate quantitative 

 measurements of these conditions were not attempted. More 

 recent work has considered the aerial environmental factors, 

 especially the evaporating power of the air, as of fundamental 

 importance in dealing with the water relations of plants. 



Briggs and Shantz- have recently maintained that the atmos- 

 pheric environmental conditions that obtain during the process 



1 Botanical contribution from the Johns Hopkins University, no. 37. 



2 Briggs, L. J., and Shantz, H. L., (1) Application of wilting coefficient deter- 

 minations in agronomic investigations. Proc. Am. Soc. Agron. 3: 250-60. 1912. 



, (2) The wilting coefficient and its indirect determination. Bot. Gaz. 



53:20-37. 1912. 



, (3) The relative wilting coefficients for different plants. Bot. Gaz. 63: 



229-35. 1912. 



, (4) The wilting coefficient for different plants and its indirect determi- 

 nation. U. S. Dept. Agric. Bur. Plant Ind. Bull. 230. 1912. 



, (5) Die relativen Welkungskoeffizienten verschiedener pflanzen. Flora 



105:224-40. 1912. 



81 



THE PLANT WORLD, VOL. 17. NO. 4, 1914 



