EFFECT OF CLIMATIC FACTORS ON WATER REQUIREMENT, 
61 
Table LI. — Comparison of evaporation and water requirement in Colorado and Texas, 
according to Briggs and Shantz (1913. p. 
Wheat. 
Sorghum. 
Years and 
stations. 
Period of growth. 
Evapora- 
tion. 
Water re- 
quire- 
ment. 
Period, of growth. 
t- Water re- 
E Uon ™- 1 ***■ 
uon - ment. 
Ac- Rel- 
tual. ative. 
Ac- Rel- 
tual. ative. 
Ac- Rel- 
tual. ative. 
A,- 
tual. 
Rel- 
ative. 
1910. 
Akron. Colo... 
Amarillo, Tex. 
Apr. 18 to Aug. 2.. 
Apr. 5 to July 19.. 
.- ' 100 
34. 122 
664 
853 
100 
128 
Mav 25 to Sept. 28. 
May 10 to Aug. 28. 
33. 100 
37.7 114 
356 
359 
100 
101 
1911. 
Akron, Colo... 
Dalhart, Tex.. 
Mav 13 to Aug. 2.. 
Apr. 2o to July IS. 
24. 8 100 
28. 5 115 
468 
673 
100 
143 
Mav 12 to Sept. 4.. 
May 14 to Sept. 12. 
35.0 100 - - 
41. 9 120 313 
100 
105 
CONCLUSIONS. 
The data here presented show clearly that the water requirement 
is profoundly affected by atmospheric conditions. Measurements of 
the water requirement conducted during different periods of the year 
show great differences. Experiments conducted at different places 
during the same period, using the same variety, give different values 
for the water requirement, owing to differences in the climatic con- 
ditions. Even though the methods and soil conditions are the same 
for two different years, profound differences are often recorded in the 
water requirement. 
EFFECT OF AIR TEMPERATURE OX THE WATER REQUIREMENT. 
The effect of temperature on the water requirement of plants does 
not appear ever to have been investigated under control conditions. 
Seasonal changes in temperature are accompanied by changes in the 
saturation deficit, so that the differences observed in the water require- 
ment of plants resulting from the march of the seasons can not be 
attributed to temperature alone. The investigations which have so 
far been made on this subject have only a qualitative bearing. See 
Fittbogen (1874), Table XL VIII (p. 59); Hellriegel (1883), Table 
XLIX (p. 59) ; King (1905), Table XV (p. 27) ; Von Seelhorst (1910), 
Table LIX (p. 69); and Briggs and Shantz (1913), Table L (p. 60) 
and Table LI (p. 61). 
EFFECT OF SHADE ON THE WATER REQUIREMENT. 
It is well recognized that sunlight is an important factor in increas- 
ing transpiration. It is also known that in ordinary sunlight more 
solar energy is received by the plants than is necessary for photo- 
synthesis. It seems evident, therefore, that an increase in solar in- 
tensity would cause an increase in the rate of loss of water from the 
plant without changing the rate of carbon fixation. Under such con- 
285 
