Transpiration and Water Movement 85 



individuals growing in the 

 field l may be made the 

 objects of observation and 

 comparative study. 



Experiments made with 

 abscised branches may not 

 be typical, for the shoots are 

 in abnormal relations, lack- 

 ing the usual organs of absorption, as 

 well as the special soil conditions ; and 

 since there is, further, a certain re- 

 sponse to the injury received, the 

 results of experiments made with plant 

 parts do not, perhaps, represent the 

 loss under natural conditions. These 

 parts may be employed, nevertheless, 

 for demonstration and for determining 

 more or less accurately the relative 

 rate of loss under different conditions. 

 Transpiration may be most accu- 

 rately determined by using potted 

 plants, observing the precautions in- 

 dicated with respect to evaporating 

 surfaces, and weighing at successive 

 intervals. Special recording balances 

 have been constructed and used for 

 this purpose, but ordinarily such de- 

 vices are unnecessary to demonstrate 

 principles and limiting conditions. 



1 Freeman, G. F., A Method for the Quan- 

 titative Determination of Transpiration in 

 Plants. Bot. Gaz., 46: 118-129, 1908. 



JG 23 Burette po _ 



tometer ; shoot fitted 

 with rubber tissue. 



