228 BRIGGS AND SHANTZ : WILTING COEFFICIENT OF PLANTS 



PLANT PHYSIOLOGY.— The wilting coefficient for different 

 plants and its indirect determination. 1 Lyman J. Briggs 

 and H. L. Shantz. To appear in Bulletin 230, Bureau of 

 Plant Industry. 



The object of this investigation was to determine the extent of 

 the variation exhibited by different plants with respect to the 

 minimum point to which they can reduce the moisture content 

 of the soil before permanent wilting occurs. It has heretofore 

 been believed that plants differ widely in this respect and that 

 drought resistance is in part due to the additional supply of water 

 which is available to some plants thru the greater force which 

 they exert upon the soil moisture. The results of this investi- 

 gation have led us to conclude that the differences exhibited by 

 plants in this respect are much less than have heretofore been 

 supposed, and are so small as to be of no practical utility from the 

 standpoint of drought resistance. As compared with the great 

 range in the wilting coefficients, the small differences arising from 

 the use of different species of plants in determining the wilting 

 coefficient become almost insignificant. 



The moisture content of the soil corresponding to the wilting 

 of a plant growing in a confined soil mass is usually spoken of 

 as non-available moisture. We have found that plants are cap- 

 able of reducing the moisture content of the soil far below that 

 corresponding to the wilting point, and that a steadj r loss of mois- 

 ture goes on through the plant tissues even after the death of the 

 plant. The moisture content at the wilting point can not then 

 be considered as non-available, and we have adopted the term 

 wilting coefficient as expressing more specifically the moisture 

 content of the soil corresponding to the permanent wilting of 

 the plant. 



The wilting coefficient is then defined as the moisture content 

 of the soil (expressed as a percentage of the dry weight) at the 

 time when the leaves of the plant growing in that soil first under- 

 goes a permanent reduction in the moisture content as the result 



'Presented before the Botanical Society of Washington, October 9, 1911, and 

 before the Philosophical Society of Washington, October 14, 1911. 



