SOIL MOISTURE AND TO EVAPORATION. 



57 



be taken to represent the conditions just preceding the wilting of the 

 plant. 



The curve for rates of relative transpiration and those for tempera- 

 tures and evaporation rates, for the period following 3 h 30'" p.m., August 

 16, are given in the usual manner in figure 11. Relative transpiration 

 is seen to vary from a minimum of 0.029, at 8 p.m., August 16, to a 



.256 



2ZO 



.143 



.OS1 



/:OOp.m. 



12. 30 p.m. 



.024 

 9:00p.m. 



O62 



058 



.032 

 .OI5 



93 93 

 ~ 



90.S/ 



/ 



86.5 



.048 



.036J 

 .03Z 



88 \ 



.063 



,'84 



,O5i 

 '.O4+ 



80 



/J?--- 76 



\.Of2 .012 



'.O7O 



.042 



.021 



.Ol 5 



6:30 D. m 

 Aug./ 3 



6:3 p.m. 

 Aug. 14 



6:30 a.m. 

 Aug.lS 



FIG. 12. Curve of relative transpiration for three plants of Boerhavia, August 13-15, 1904. 



maximum of 0.371 at 10 a.m. , August 17. The minimum occurred with 

 an air temperature of 75 F. and an evaporation rate of 0.029, while 

 the maximum occurred with a temperature of 79.5 F. and an evapora- 

 tion rate of 0.035 gram. It will be seen that the regulation of water 

 loss causes a variation in relative transpiration from unity as a maximum 

 to about one-twelfth as a minimum. / 



