WATER OF SOIL IN ITS RELATION TO PLANTS 191 



ments of corn under greeniionse conditions, tliat an increase 

 in the percentage iiumidity from 42 to 65 lowered the 

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

 sunshine, and wind yary 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 w^ould 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 ^ 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^ at Lincoln, 

 Nebraska, with maize grown in a loam soil : 



Table XXXV 



EFFECT OF SOIL-MOISTURE ON TRAN"SPIRATIOISr. 



Baeley — ^Hellriegel 



Maize — Montgomery 



SOIL-MOISTURE 



PEBOENTAGB 



OW TOTAL 



CAPACITY 



TRANSPIRATION 

 RATIO 



SOIL-MOISTURE 

 PERCENTAGE OF 

 TOTAT, CAPACITY 



TRANSPIRATION 

 BATIO 



80 

 60 

 40 

 30 

 20 

 10 



277 



240 

 216 

 223 

 168 

 180 



100 

 80 

 60 

 45 

 35 



290 

 262 

 239 

 229 

 252 



^Hellriegel, H., Beitrage bu den NaturwisseMchaftUclien Grundlage 

 des Ackerhaus, Seite 629, Braunschweig, 1883. 



^ Montgomery, E. G., Methods of Determining^ the Water Bequire- 

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



