216 



PLANT SOCIOLOGY 



According to Maximov (1929) and Knight (1922), wilting is 

 clearly shown by the loss of turgor before there is any visible indication 

 of the condition. The amount of water that leaves may lose without 

 visible wilting is a useful indicator of xerophytism, and the ability to 

 recover from wilting is one of the most rehable indicators of drought 

 resistance. Numerous American investigators such as Fuller (1914), 

 Weaver (1914), Thone (1923), and Shantz and Piemeisel (1925) have 

 come to regard the wilting coefficient as a most useful constant by 



Augusf 



FlQ. 111. — Range of soil moisture and corresponding wilting coefficients (TF.C) in three 

 different associations in Nebraska. (.After Weaver.) 



which to relate the availability of the soil moisture to the plant 

 community. 



The differences in the wilting point of various plant communities 

 may be considerable. Communities requiring a large amount of 

 available water usually have a higher wilting coefficient than those with 

 lesser demands upon soil water (Fig. HI). In other words, the more 

 mesophytic communities usually develop on soil with high water 

 capacity. 



The wilting coefficient rises in the course of mesophytic successions 

 with the changes which accompany soil development (the enrichment 

 of the soil with humus, etc.), as Fuller (1914) was able to prove in the 

 Great Lakes region of North America (Table 23). 



The determination of the wilting coefficient may be made directly, 

 according to the directions given by Briggs and Shantz, or indirectly 

 through the moisture equivalent, using the equation: 

 Moisture equivalent 

 1.84 



= wilting coefficient. 



