[Vol. 2 



466 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



For the conductivity work herein reported the following 

 apparatus was used: 



Wheatstone bridge (Central Scientific Co., catalogue number, 



2475) ; 

 Resistance box, 11,110 ohms (Central Scientific Co., catalogue 



number, 2444) ; 

 Induction coil (Eimer and Amend, catalogue number, 4100) ; 

 Dry battery cells (Eimer and Amend, catalogue number, 592) ; 

 Conductivity cell, Freas (Eimer and Amend, catalogue number, 



5202); 

 Telephone receiver (Central Scientific Co., catalogue number, 



2355) ; 

 Thermometer graduated to 1/10°C; 

 Water tank holding 50 gallons, specially constructed for the 



purpose, pilot flame underneath ; temperature regulated to 

 1/10°C; 

 Tiffany laboratory motor with which to operate a stirring 

 apparatus in the tank. 



In the method employed for the work the procedure given 

 below was consistently followed: the tumblers were always 

 filled to approximately the 250 cc. level with either the solu- 

 tion or redistilled water, depending on the culture. Before 

 taking readings, doubly distilled water was added to bring 

 the water or solution up to the original level, if the transpira- 

 tion loss since the previous reading made the addition neces- 

 sary. This was of course essential in order to keep the con- 

 centration factor under control. Readings in all cases were 

 taken at 25° C. The control of temperature exactly to within 

 1/10° C. was comparatively easy by the use of the pilot flame 

 underneath and the stirring apparatus in the tank of water. 



For absolutely accurate and final quantitative determina- 

 tions or ultimate values, as were required, for example, in the 

 case of the standardization measurements for the cell constant 

 with N/50 KC1, or the determination of the specific con- 

 ductivity of the doubly distilled water, the greatest precau- 

 tions possible were taken in regard to the conductivity cell 

 and the concentration of its contents. But in making hun- 

 dreds and even thousands of determinations, most of them as 

 rapidly as accuracy permitted, due to the time factor involved, 

 it was both impossible and unnecessary to dry the cell after 

 each reading, since relative, and not absolute, values were 



