586 STATE BOARD OF AGRICULTURE. 



period. It also shows that duriug a period of a little over 48 hours the 

 resistance had fallen from 29,595 ohms to 13,735 ohms. 



It is instructive to compare these results witli the results obtained when 

 tap water is the culture solution. The experiment is the same as the 

 preceding in every respect except that the culture solution is tap water 

 and the number of seedlings used thirteen. 



At 9:30 A. M. 3/13/15 the resistance was 272.272 ohms. 

 At 11:40 A. M. 3/13/15 the resistance was 271.180 ohms. 

 At 2:00 P. M. 3/13/15 the resistance was 209.088 ohms. 

 At 9:20 P. M. 3/13/15 the resistance was 270.G20 ohms. 

 At 9:30 A. M. 3/14/15 the resistance was 2G9.088 ohms. 

 At 3:30 P. M. 3/14/15 the resistance was 269.024 ohms. 



During the 30 hours in which the experiment was running there was 

 very little change in the resistance. The concentration seemed such as 

 would allow absorption and excretion of electrolytes at equal rates. 



Experiment VI. 



For some time it has been known that roots excrete GOn. To what ex- 

 tent the decrease in resistance is due to the presence of CO, is not defi- 

 nitely known. The following experiment shows, however, that the greater 

 part is not due to the presence of CO2 as might be thought. In this case 

 about 13% of the change in concentration is probably due to carbon 

 dioxide alone. 



Three clean Jena glass beakers were selected. These three contained 

 equal quantities of distilled water having the same conductivity. This 

 was accomplished by washing them successively in conductivity water 

 until the wash water possessed the same resistance as the original water. 

 The experiment was then started. In the first beaker no seedlings were 

 placed. Four seedlings were put in the second beaker and the third re- 

 ceived eight. They were put aside for 24 hours and then the conductivities 

 were determined. The seedlings were removed and the COo driven off 

 by heat. As much care as possible was taken not to decrease the volume 

 of fluid but yet be sure of driving off the carbon dioxide. Pure hot melted 

 parafiQne was poured on immediately and the beaker of water so covered 

 was put away in the ice chest for the parafifine to harden. Pure paraffin 

 is inert chemically and no error larger than the experimental error is 

 believed to enter here. After a few hours the beaker was placed in the 

 water bath to bring the solution to the proper temperature. The paraffin 

 cap was now removed and the conductivity of the solution measured. 



Before Boiling. 



No. seedlings Bridge Reading Resistance Conductivity. 



490 93,690 1.67x10-6 



4 442 26,182 5.98x10-6 



8 538 17,174 9.12x10-6 



After Boiling. 



500 90,000 1.74x10-6 



4 570 30,112 5.20x10-6 



8 503 19,494 8.03x10-6 



