v.] WATER LIFTED BY SURFACE TENSION mi 



During the first period, the month of May, a dry 

 pell prevailed, only 018 inch of rain fell, while the 

 ivaporation amounted to 3-45 inches ; despite this 

 oss the top foot of soil only contains 1 inch of water 

 ess than at the beginning, so that the rest of the 

 :xcess of evaporation over rainfall must have come 

 rom the subsoil, which had in fact to furnish 2-27 

 nches. In the second period more water fell as rain 

 han was evaporated ; the surface soil gained 1-4 inch, 

 /hich did not account for all the excess of rain over 

 vaporation, a further -17 inch must have descended 

 nto the subsoil. 



The extent to which the deeper subsoil below the 

 ange of the roots of the crop is able to supply the 

 urface soil and the growing plant with water by 

 apillarity has been the subject of considerable discus- 

 ion. It has been very generally considered that the 

 plift which must go on from the permanent water 

 able, at whatever depth, provided the subsoil or 

 nderlying rock is of the texture that permits of 

 apillary movements, must be a factor in the supply of 

 'ater to the crop during protracted periods of drought, 

 t seems probable, however, that the amount so lifted 

 an be of no material service, and that the effective 

 apillary movements are those of comparatively small 

 ange which bring the water in the soil a few inches 

 r even fractions of an inch to the actual surface of 

 hie root hairs. In the first place, as indicated above 

 i King's experiments, the rate of capillary uplift 

 iminishes very rapidly as the distance from the water 

 able is increased. At Rothamsted (p. 85) the two drain- 

 auges consist of isolated blocks of undisturbed soil, 

 ne 18 inches, the other 6 feet deep. The surfaces 

 f both are freely exposed to rainfall and evaporation. 

 )ver a long period of years the proportion of the 



