Journal of Agricultural Research 
Vol. VII, No. 4 
156 
The transpiration of the plants in each pot,as determined by the weigh¬ 
ings, was plotted daily as a check on the weighing and watering records. 
The daily transpiration of the first five crops of the 1914 series, traced 
directly from the original graphs, is shown in figure 1. These graphs are 
typical of the series and show the proportional response of the individual 
pots of plants to the fluctuations in weather factors. The daily trans¬ 
piration of each crop is represented by the mean value of the six indi¬ 
vidual determinations, which minimizes slight errors in the weights of 
the individual pots, and abnormalities in the transpiration rate of indi¬ 
vidual plants. Inspection of figure 1 will show the close agreement of 
the individual determinations. While the plants in some pots of a given 
series transpire more than others, owing to differences in stand or size 
of the plants, the daily fluctuations are very nearly proportional. 
The weather factors measured included solar radiation, air temperature, 
wet-bulb depression, and wind velocity. These factors, as well as 
evaporation, were integrated for each day. The solar radiation and the 
wet-bulb depression were measured by differential thermographs and the 
air temperature by a standardized air thermograph. The wind velocity 
was recorded by an anemometer located 3 feet above the ground. The 
evaporation was measured by means of a shallow blackened tank 6,540 
sq. cm. in area, exposed at the level of the plants, and also by means of 
a large tank 8 feet in diameter and 2 feet deep, with the water surface 
at the ground level. 1 
DAILY TRANSPIRATION AND THE DAILY INTENSITY OF THE 
WEATHER FACTORS DURING THE GROWTH PERIOD 
MEASUREMENTS IN 1914 
The daily transpiration of 22 crops grown in 1914 is given in Table I, 
the daily loss being expressed in kilograms per pot. The small grains 
were well established before the daily weighings were begun, and had 
lost during the previous month approximately 10 per cent of the total 
water transpired during the entire growth period. The daily weighings 
in the case of the other crops cover the entire growth period after the 
daily loss had reached one-tenth of a kilogram or more per pot. 
1 For a further description of the methods and apparatus employed, see Briggs and Shantz, op. cit., 1916, 
p. 584-585, 625; and Briggs, E. J., and Belz, J. O. Dry farming in relation to rainfall and evaporation. 
U. S. Dept. Agr. Bur. Plant Indus. Bui. 188, p. 17. 1910. 
