1 68 plAnt world. 



of the potometer readings, and lost lo mg. according to 

 weighings at the start and close of the test, which indicates 

 that the inherent error of the potometer method is even 

 greater than usual in the case of leaves with water storage 

 tissue. All figures given show the rate of loss per loo sq. 

 cm. per hour. 



Period Rate 



1.30 to 2.00 p.m. 46.5 mg. 



2.00 to 3.00 72.4 



3.00 to 4.00 95.2 



4.00 to 4.30 78.2 



4.30 to 5.30 39.1 



5.30 to 7.00 34.3 



7.00 to 8.00 26.0 



8.00 to 10.00 25.8 



. 10.00 to 7.00 a.m. 19.7 



7.00 to 1.30 p.m. 57.4 



While these data serve to give a good notion of the 

 daily play of the transpiration rate, they are deceptive as to 

 the absolute amount, as shown by another set in which an 

 entire plant with unbroken root system and four good leaves 

 was placed in a jar of water sealed with plastocene. This 

 test was carried out first in the laboratory and later out of 

 doors under natural conditions of the rain forest. In the 

 first case the temperature ranged from 57" to 69^ and the 

 humidity from 75% to ^o^/c . In the second case the weather 

 was cloudy with intermittent fog and a good breeze, the 

 temperature ranging between 60 and 70° and the humidity 

 between 85% and 92^/c;. 



Period Rate 



2.00 to 5.30 p. m. 125 mg. 



5.30 to 9.00 42 



9.00 to 6.30 a. m. 17 



8.00 a. m. to 5.30 p. m. 159 



These figures serve to show what is much more nearly 

 the normal rate of transpiration in Slelis at such times as it 

 is abundantly supplied with water, but not subjected to sun- 

 shine. An opportunity to ascertain the rate under insolation 



