200 



BOTANICAL GAZETTE 



[march 



weather had been unusually hot and windy. The time of the 



season was that at which the draft upon the subsoil moisture might 



be expected to show the most marked effect. In the soil of the 



first foot we found a ratio of i .o and in that of the next 3 ft., an 



average ratio of i . 4 ; but the sixth foot, with a ratio of i . 9, appeared 



to have lost but little of the moisture which it could retain against 



downward movement. 



TABLE XI 



Moisture conditions in prairie fields near Lincoln after unusually 



dry periods 



On the second occasion, August 3, 191 1, a dry period of 65 days 

 had just been ended by a rain of 0.84 inch. Compared with a 

 normal precipitation of 9.0 inches for this period, only 2.68 inches 

 of rain had fallen, and this in light showers, while both the mean 

 temperature and the wind velocity had been somewhat above the 

 normal. As the subsoil of the second to the fifth foot appeared 

 uniformly dry it was combined into a single sample, the ratio 

 proving to be 1.3, but in the sixth to ninth foot it was 2 .0 to 2 . i. 

 The moister condition in the surface foot indicated in the table was 

 due to a shower of the day before having moistened the immediate 

 surface layers. 



From the time of the preceding to the next and last sampling, 

 June 7, 191 2, the weather on the whole was very unfavorable to the 

 accumulation of any moisture in the subsoil, and the spring of 191 2 

 was exceptionally favorable to the exhaustion of whatever available 

 water was within reach of the plant roots. The moisture conditions 

 found were quite similar to those on the preceding occasion. 



Thus the samplings, taken at times of drought when one might 

 have expected almost the lowest moisture content in the subsoil 



