182 DRY-FARMING 



spires excessively and the crops are consequently 

 more subject to drouth. 



The investigators of almost a generation ago also 

 determined beyond question that whenever a com- 

 plete nutrient solution is presented to plants, that is, 

 a solution containing all the necessary plant-foods 

 in the j^roper proportions, the transpiration is reduced 

 immenselJ^ It is not necessar\' that the plant-foods 

 should be presented in a water solution in order to 

 effect this reduction in transpiration; if they are 

 added to the soil on which plants are growing, the 

 same effect will result. The addition of commercial 

 fertilizers to the soil will therefore diminish tran- 

 spiration. It was further discovered nearly half a 

 century ago that similar plants growing on different 

 soils evaporate different amounts of water from their 

 leaves ; this difference, undoubtedly, is due to the 

 conditions in the fertility of the soils, for the more 

 fertile a soil is, the richer will the soil-water be in the 

 necessary plant-foods. The princi])le that transpira- 

 tion or the evaporation of water from the plants 

 depends on the nature and concentration of the soil 

 solution is of far-reaching importance in the develop- 

 ment of a rational practice of dry-farming. 



Transpiration for a pound of dry matter 



Is plant growth ]Dro])ortional to transpiration? 

 Do plants that evaporate nuich water grow more 



