Oct. 23, 1916 Daily Transpiration during Normal Growth Period 
197 
Y 
in which is the interest rate. From this relationship the daily rate 
of increase (daily interest) can be readily determined. 
The rate of increase may also be expressed in terms of the time re¬ 
quired for k to double in value. 
Let k x be the value of k at the time t v If k = 2k x , 
- ioa - « - 2 ’ 
a (t - Q = log 10 2 = 0.3010, 
0.3010 
Fig. ii.—G raph showing a linear relation between the logarithm of the transpiration-evaporation ratio 
of Sudan grass (grown in the open) and the time. 
The values of the coefficient a, the rate of increase r , and the time 
(t — t t ) required for k to double in value are given in Table XX for the 
various crops considered in figures 10 to 15. 
It will be seen from Table XX that the daily increase in the transpira¬ 
tion coefficient of Sudan grass during the early stages of growth was ex¬ 
tremely rapid, ranging from 16 to 21 per cent. Since this is compounded 
daily, four days are required for the transpiration coefficient to double 
in value during this active growth period. The growth rate during the 
early stages of Algeria corn and sorghum was less rapid, about seven days 
being required for k to double in value. 
