262 FRANCIS RAMALEY 



In contrast to these low water contents it may be stated that 

 two of the meadow societies showed averages of 14.8 and 16.7%. 



In our previous discussion the Erigeron multifidus society 

 was classed as hyperxerophytic. In the main series of succession 

 it was numbered 1, the Muhlenbergia-Aragallus society was 

 numbered 5 and the Muhlenhergia-Danthonia society 6. It is 

 seen that judgment from appearances as to relative amount of 

 soil water is confirmed by the determinations. 



Wilting coefficient determinations^^ of four soil samples were 

 made in the office of Biophysical Investigations, United States 

 Department of Agriculture at Washington through the courtesy 

 of Dr. Lyman J. Briggs. The figures are shown in Table III. 

 It is the greater amount of humus present in the upper part of 

 the soil that raises the wilting coefficient of ordinary dry grass- 

 land from 5.1 at 3 dm. to 7.6 at 1 dm. 



TABLE 3 

 Wilting coefficient of soil samples 



Erigeron multifidus society, at 2 dm. depth 3.5 =*= 0.1 



Ordinary drj^ grassland, at 3 dm. depth 5.1 ± 0.1 



Ground-squirrel mound 6.2 =*= 0.2 



Ordinary dry grassland, at 1 dm. depth 7.6 ± 0.2 



Comparison of tables 2 and 3 shows that while usually the 

 water content is ample yet at times it falls below the wilting 

 coefficient. This is most likely to occur in August after the 

 growing period of many of the plants is passed. Occasionally, 

 however, considerable wilting occurs in isolated spots even in 

 July, and long before seeds are ripened. 



High winds and low relative humidity are characteristic 

 features of Rocky Mountain climate; evaporation is rapid. i"* 

 To learn the relative amount of evaporation in the Muhlenbergia- 



^^ Briggs, L. J., and Shantz, H. L., The wilting coefficient for different plants 

 and its indirect determination. Bull. 200, U. S. Dept. Agric, Bur. Plant Ind., 

 1912. 



^* Ramaley, Francis, and Robbins, W. W., Studies in lake and streamside 

 vegetation, Redrock Lake, near Ward, Colorado. Univ. Colo. Studies 6: 133- 

 168, 1909. 



Ramalej^, Francis, and Mitchell, Louis A., 1911 Ic. 



