54 



decrease with rising or falling temperature. The minimum rate 

 occurs near sunrise and the maximum in the afternoon. Consumptive 

 use, in the exposed tank, is greater than evaporation and responds 

 more readily to sunlight and changes in temperature. The rate of 

 evaporation increases slowly until the water in the pan has been 

 warmed by the sun, while consumptive use increases more rapidly, 

 comes to a peak sooner, and declines more quickly. In other words 

 the plant is more sensitive to the factors causing water loss than 

 is the water in the evaporation pan. 



On the morning of August 28 temperature was less than 

 normal, and a light rain occurred shortly after noon. The effect 

 of the rain in deferring the morning increase in consumptive use 

 and in evaporation until about 2 p.m. is noticeable. The precip- 

 itation caused a small decrease in the rate of evaporation until 

 its effect was overcome by rising temperature. In general, the 

 highest air temperature occurred at about 1 p.m. to 2 p.m., while 

 the highest water temperature occurred about 2 hours later. The 

 same interval also is noticeable in minimum temperatures. Obser- 

 vations elsewhere have shovm the highest consumptive use of water 

 by tules occurs approximately at the time of highest air tempera- 

 tures, although such is not the case in this instance. 



Coastal winds at the Prado station, in combination with 

 high temperatures, are responsible for a continued increase in 

 both evaporation and consumptive use until midafternoon and a 

 higher rate of loss than at Santa Ana. The observed annual loss 

 from the exposed tule tank reached a total of 251.3 inches or 

 325 per cent of the evaporation for the same period. The maximum 

 daily loss was 3.6 inches. 



Excessive rates of consumptive use of water by tules in an 

 isolated tank were found also at the San Bernardino station. 

 This tank was set in a Bermuda grass field. Vhile the tule growth 

 was stunted by exposure, the water consumed amounted to 170.88 

 inches in 11 months. In southern California records are taken for 

 each month of the year; although tule and cattail stems die in the 



