26 



about the c -.s is plant tra.iio_;_^J.Xtt!.J v; li, J j' the compari- 

 son is made for periods of a day or more. Of coturse the 

 two rates do not vary proportionally vrithin the day period, 

 since the internal conditions of the plant exhibit a neculiar 

 daily march, but m th such details this study does not need 



^ r-^ ...... 



Ti;,n i-o"^ ^ -^ i" -^ - '- -P =1 



o r' ^ -v» ^- -V- 



soil moisture and to evaporation. Carnegie Inst, Wash, Pub, 

 50. 1906. 



to deal. It has been supposed therefore, tha-^ tiae effective- 

 ness of the external conditions to influence the transpira- 

 tion rates from the plants of this stiidy was approximately 

 measured by the corresponding evaporation rates from the 

 ^tmometer. The atraometer re dings have been reduced. In 

 every case, to mean daily rates for the E-reek and 4-week 

 periods taken as indices of the evaporating power of the air 

 as it affected the transpiration rates of the plants. 



