Oct. i8, 191S 



Automatic Transpiration Scale 



131 



3VO 



aso 



/so 



/oo 



% so 



I . 



300 



\aso 



rate which is momentarily too high. Special provision is made to prevent 

 two balls being delivered to the beam in rapid succession, and no record 



is made unless a ball is — — — 1 



actually delivered to - - - „. « 



the ball container on 

 the beam. Four of 

 these automatic scales 

 have been in use dur- 

 ing the past four sum- 

 mers at Akron, Colo., 

 and continuous records 

 have been secured dur- 

 ing these periods. The 

 results of these meas- 

 urements will be dis- 

 cussed in other papers. 

 A brief review is also 

 given of other forms of 

 transpiration bal- 

 ances, which are di- 

 vided into two classes : 

 Those operating on the 

 step-by-step principle, 

 which includes the bal- 

 ances here described, 

 and those of the con- 

 tinuous-record type. 

 The first class includes 

 balances in which the 

 adjustment is secured 

 by adding small 

 weights (solid or 

 liquid) of equal mass 

 or by moving a coun- 

 terpoise in uniform 

 steps. In the second 

 class the plant is suspended from a spring, or from a variable lever, or 

 is mounted (directly or indirectly) on a float. 



' /oo 



I- 



\900 

 \800 

 ^700 



soo 



'^00 



eoo 



;. — Transpiration graphs corresponding to the three records 

 given in figure i6, plotted in rectangular coordinates. 



LITERATURE CITED 



Anderson, A. P. 



1894. On a new registering balance. In Minn. Bot. Studies, v. i, 



177-180 



Blackman, V. H., and Paine, S. G. 



1914. A recording transpirometer. In Ann. Bot., v. 28, no. 109, p. 

 ipl 



Cited in this 

 article on page - 



pt. 4> P- 



[ 09-1 13, 



117 



119 



