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EDITH BELLAMY SHREVE 



in determining the volumetric center of the aerial parts. It is possible to find a 

 probable maximum error by supposing the center of transpiration which is se- 

 lected, to be wrong a given proportion of the length of the plant, first in one direc- 

 tion and then in the other. 



An example will best illustrate the method of calculation. From table 8 it is 

 found that Plant No. 30, the centers of whose pot and aerial parts are 5.5 cm. 

 and 15 cm. from the knife edge, showed the following readings on the night of 

 June 22-23. At S.51 p.m. the system was balanced by means of the screw and 

 then weighed as a whole on balances. At 8.29 a.m. the next morning the plant 



Fig. 9. Apparatus used for the determination of transpiration and absorp- 

 tion in experiment 10. At the left may be seen the device for automatically 

 recording the movements of joints. 



was taken from the dark room and again placed in a horizontal position, resting 

 upon its knife edge. The plant rose so that no point of equilibrium could be 

 found, showing that the plant had lost more water than it had gained from the 

 soil during the night. When 3.5 grams were placed on the pointer at a distance 

 of 5.5 cm. from the knife edge the system was restored to equilibrium. The bal- 

 ances showed that the system had lost 5.5 grams during the period. If the equa- 

 tion a = a represents the condition of equilibrium at 8.51 p.m. and .r the amount 



