58 THE BIOLOGY OF FLOWERING PLANTS 



Nardus stricta, and only a ninth to Vacciniiim Vitis-Idcea ; 

 his plants were only protected from rain. Here the factors 

 affecting the shoot also come into play ; a better idea is 

 obtained of the plant's reaction in a natural environment, 

 but a less accurate indication of the action of the soil alone. 

 The critical review by Blackman (19 14) should be consulted. 

 Briggs found the wilting coefficient to be very different 

 in different types of soil, and he related it to various physical 

 soil constants. Table XIV gives some of his results, and 

 shows also for comparison the coefficient as calculated from 

 the equation which relates it to soil constitution. 



SandsXo*oiH-siltxo'i2+clay Xo'57 



:W. Coeff. 



I ±0*025 



o J (coarse sand particles between 2 and 0*25 mm. 

 jfine „ „ „ 0*25 and 0*05 mm. 



Silt „ „ 0*05 and 0*005 mm. 



Clay „ less than 0*005 mm. 



TABLE XIV 



Composition and Wilting Coefficients of Different Soils 



The agreement between the observed results and those 

 calculated is remarkably good. Formulas were also 

 devised connecting the wilting coefficient with various soil 



