WATER OF SOIL IN ITS RELATION TO PLANTS 191 



ments of corn under greenhouse conditions, that an increase 

 in the percentage humidity from 42 to 65 lowered the 

 transpiration ratio from 340 to 191. In general, temperature, 

 sunshine, and wind vary together in their effect on transpira- 

 tion. That is, the more intense the sunshine, the higher is 

 the temperature, the lower is the humidity, and the greater 

 is likely to be the wind velocity. All this would tend to raise 

 the transpiration ratio. 



From the soil standpoint, however, the factors inherent 

 in the soil itself are of more vital importance as regards tran- 

 spiration, since they can be controlled to a certain extent un- 

 der field conditions. An increase in the moisture content of a 

 soil usually results in an increased transpiration ratio. The 

 work of Hellriegel 1 with barley grown in quartz sand con- 

 taining a nutrient solution may be cited in this regard, to- 

 gether with the data obtained by Montgomery 2 at Lincoln, 

 Nebraska, with maize grown in a loam soil : 



Table XXXV 



EFFECT OF SOIL-MOISTURE ON TRANSPIRATION. 



1 Hellriegel, H., Beitrdge zu den Naturwissenschaftlichen Grundlage 

 des Aclcerbaus, Seite 629, Braunschweig, 1883. 



2 Montgomery, E. G., Methods of Determining # the Water Require- 

 ments of Crops; Proc. Amer. Soc. Agron., Vol. 3, p. 276, 1911. 



