214 



PLANT SOCIOLOGY 



meadow (probably Mesobrometum) near Zofingen, according to Burger 

 (1922, p. 106) in seven determinations spread over all seasons, a 

 maximum deviation of only 2.2 per cent of volume from the mean was 

 recorded; in the mixed deciduous forest the maximum deviation 

 amounted to 3.3 per cent of the volume. With depth the water 

 capacity of the soil examined was found in most cases to decrease. 



In the ecological characterization of plant communities the water 

 (and air) capacity of the soil will in the future demand more attention. 



Table 20. — Water and Aie Capacity of the Soil of a 100-year-old Deciduous 



Forest at Zofingen 

 (After Burger) 



Coefficients of Soil Moisture. — We have seen that water capacity, 

 along with granulation, is especially affected by the expansible colloid 

 complexes of the soil. Their quantitative distribution in the soil thus 

 affords the best data for the estimation of its water capacity. Basing 

 his calculations upon this assumption, Crump (1913) has computed a 

 soil-moisture coefficient which he calls the "standard index of soil 

 moisture." The soil-moisture coefficient is expressed in terms of the 

 percentage of water content of the air-dried soil (around 15°C.), 



_ water content \ 

 humus content/' 



divided by the humus content I K 



Since the 



Table 21. — Coefficient of Soil Moisture in Different Facies of Oak 



Forests 



Facies of the forest floor 



Water, 

 per cent 



Humus, 

 per cent 



Coefficient of soil 

 moisture, per cent 



Scilla non scripta 

 Carex pendula. . . 

 Holcus mollis . . . . 



24.4 

 30.5 

 281.2 

 248.3 

 31.2 

 28.6 



6.9 

 9.3 

 30.3 

 26.7 

 12.9 

 12.1 



3.5 



3.25 



9.3 



9.28 



2.4 



2.36 



