1 1 CLARK— ON WATER CONTENT 



W2 - Wl = weight of fresh leaves 



W3 - Wl = weight of dried leaves 



(W2 - Wl) - (W3 - Wl) = weight of water in fresh leaves 



W2 - W3 = weight of water in fresh leaves 



W2-W3 



r— — ZZ7- X 100 = water content, based on weight of the fresh leaves. 



Wz - W 1 



For every hour of the 24 consecutive hours, water content for both 

 Populus tremuloides and Populus grqudidentata, based on the weight 

 of the fresh leaves, was reckoned. 



Due to lack of anemometers at the Station, only general observa- 

 tions were made as to air movement; no data were got for air pressure; 

 measurements of water content of soil were eliminated; and general 

 weather conditions were roughly summed up as cloudy, clear, rain, etc. 

 Percentages of relative humidity were obtained from the "Marvin 

 Psychometric Tables." Percentages of light intensity were calculated 

 according to the following formula: 



— = light intensity, where 

 bx 



x = number of seconds required to produce a good tint on the 



Solio paper in the shade to be tested. 

 y= number of seconds required to produce a good tint in the 



open at the same time, 

 a = number of seconds required to produce on the standard a 



tint to match x. 

 b = number of seconds required to produce on the standard a 



tint to match y. 



The standard was made by exposing the Solio strip for 2, 4, 6, 8, 

 etc., seconds at noon on a bright, sunny day, July 4. All Solio strips 

 were kept carefully in a dark, dry place and were later developed in a 

 solution consisting of a teaspoonful of Hypo dissolved in 4 ounces of 

 water. 



Since these figures in light intensity show only the percentage of all 

 available light that is received at each particular reading, the results 

 are practically valueless so far as daily or seasonal consecutive work 

 in water content and transpiration values are concerned. 



Data and Results 



From readings of the various phases of the experiments, the follow- 

 ing tables were compiled: 



