184 DRY-FARMING 
the soil solution by the addition of artificial fertilizers 
enabled the plant to produce dry matter with less 
water. He further found that if a soil is properly 
tilled so as to set free plant-food and in that way to 
enrich the soil solution the water-cost of dry plant 
substance is decreased. Hellriegel, in 1883, con- 
Fic. 44. Interior of olive orchard, Sfax, Tunis. Note the great distances 
between the trees and the perfectly clean soil culture. 
firmed this law and laid down the law that poor 
plant nutrition increases the water-cost of every 
pound of dry matter produced. It was about this 
time that the Rothamsted Experiment Station re- 
ported that its experiments had shown that during 
periods of drouth the well-tilled and well-fertilized 
fields yielded good crops, while the unfertilized fields 
