CURRENT LITERATURE 



NOTES FOR STUDENTS 



The wilting coefficient. — The importance in ecological work of some method 

 of determining what portion of the soil moisture is available for the growth of 

 plants caused ecologists to welcome the "wilting coefficient" of Briggs and 

 Shantz 1 as an important constant for the investigation of plant associations. 

 The general conclusion that for any given soil the wilting coefficient is largely 

 independent of the kind of plant or of the external conditions under which the 

 plant grew and wilted was directly at variance with the ideas of plant physiolo- 

 gists and was soon questioned. Unfortunately, in the extensive and careful 

 experiments of Briggs and Shantz there was no exact quantitative description 

 of the atmospheric factors under which the experiments were carried out. 

 Limiting these factors rather definitely, Caldwell 2 found that only when 

 wilting was slowly brought about under rather moist conditions was the wilting 

 coefficient, or "the ratio of soil moisture content at permanent wilting," the 

 same as that determined by Briggs and Shantz. Similar plants placed under 

 the high transpiration condition of the desert atmosphere at Tucson wilted 

 with a soil moisture content 30-40 per cent in excess of the wilting coefficient 

 for the humid aerial conditions, the difference being greatest in soils with a low 

 saturation capacity, although under a given set of atmospheric conditions the 

 wilting coefficient was approximately a constant for each of the soils used. In 

 order that the wilting coefficient may be determined solely by soil conditions, 

 therefore, it is only necessary that the evaporating power of the air shall not 

 exceed a certain limit, but where this limit lies, beyond which this coefficient 

 is decidedly greater than that determined by Briggs and Shantz, was not 

 determined. 



Blackman3 has recently reviewed the situation, including Crump's 4 new 

 method of expressing the soil moisture (coefficient of humidity) and has aptly 

 pointed out what appears to be some of the important related ecological prob- 

 lems of the water relations of plants urgently requiring investigation. They are 

 (1) the confirmation of the results of Briggs and. McLane (on the moisture 

 equivalent of soils), and of Briggs and Shantz; and (2) how far the formula 



1 See Bot. Gaz. 53:20-37, 229-235. 1912. 



2 Caldwell, J. S., The relation of environmental conditions to the phenomenon 



of permanent wilting in plants. Physiol. Res. 1:1-56. 1913. 



'BZACKMAH, V. H., The wilting coefficient of the soil Jour. Ecol. 2:43-5 



-so 



1914 



« See review in Rot. Gaz. 57:85. 1914. 



280 



