CHAPTER IX 



REGULATING THE TRANSPIRATION 



Water that has entered the soil may be lost in 

 three ways. First, it may escaj^e by downward 

 seepage, whereby it passes beyond the reach of plant 

 roots and often reaches the standing water. In dry- 

 farm districts such loss is a rare occurrence, for the 

 natural precipitation is not sufficiently large to con- 

 nect with the country drainage, and it maj^, therefore, 

 be eliminated from consideration. Second, soil- 

 water may be lost by direct evaporation from the sur- 

 face soil. The conditions prevailing in arid districts 

 favor strongly this manner of loss of soil-moisture. 

 It has been shown, however, in the preceding chapter 

 that the farmer, by proper and persistent cultivation 

 of the topsoil, has it in his power to reduce this 

 loss enough to be almost negligible in the farmer's 

 consideration. Third, soil-water may be lost by 

 evaporation from the plants themselves. While it 

 is not generally understood, this source of loss is, in 

 districts where dry-farming is properly carried on, 

 very much larger than that resulting either from seep- 

 age or from direct evaporation. Wliile plants are 

 growing, evaporation from plants, ordinarily called 

 transpiration, continues. Experiments performed 



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