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 



.^^o 



.OS 5 



/.oop.m. 



\ 



J2/ 



.IO9 



027 



12:30 p.m. 



04-8 



.024 



9:00 p.m. 



06^ 



.058 



.032 



x 



.0/5 



!2:3Op.m, 



90.5/ 



93 93 



\ 



88\ 



86.5 



.06 3 



.OS 

 '.O44- 



80 



0361 



.03^ 



043 



/.?--- 76 



\.OI2 .012 



79 



'.0/3 



.042 



.021 



.OI5 



6:30 p.m 



Aug./ 3 



: 3d a.m. 



6:3 p.m. 



6:30 a.m. 

 Aug./ 5 



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. 



