94 



BRIGGS: THE LIVING PLANT AS A PHYSICAL SYSTEM 



to the transpiration or water loss from the plant during a series 

 of uniform days, providing transpiration and evaporation are 

 influenced in the same way by the changes in the weather. Our 

 problem then is to determine how the transpiration corrected 

 to the basis of uniform days varies with the time, our assumption 

 being that the daily transpiration is dependent upon and is a 

 measure of the size of the plant. 



-/. <? 



-/. 2 



- /.o 





-2.8 



2.6 



■2.4 



-2. 



-2 



P2 24 26 2G 30 2 4 



6 8 /O /2 /4 /6 



Fig. 1. Graph showing linear relationship between the logarithm of the trans- 

 piration-evaporation ratio of Sudan grass and the time. After Briggs and Shantz. 



If now we return to our original hypothesis, that the rate of 



change in the size of the plant is proportional to the size of the 



plant itself, we will have by substituting the transpiration- 



T 

 evaporation ratio — = k for the weight m of the plant in our 



Mi 



original equation (6) 



dk 



dt 



= dik 



(6a) 





