Conductivity under Geotropic Stimulation. 



359 



ANGLE WITH VERTICAL 

 Fig. 12. 



Differential Permeability of Upper and Under Sides. 



Preliminary experiments indicated that the permeability of both upper and 

 under sides of the root-tip increased, and this was further investigated in the 

 following experiments. 



Experiment 6 : E = 7000 ohms. 



Angle -svitli rertical ... 0° 0= -10'' +10° -20° +20° 



Total resistance 8696 8730 8217 8418 7958 82.50 



Decrement of resistance ... — — 513 312 772 480 



Uxperiment 7 : E = 6000 ohms. 



Angle tvith vertical ... 0° 0° -45° +4.5' -70' +70' -90° +90° 



Total resistance 6073 6073 5194 5705 485] 5606 4753 5584 



Decrement of resistance ... — — 879 308 1222 467 1320 489 



The results of Experiments 6 and 7 are graphed in fig. 13. The relative 

 flatness of the upper part of the curve is again demonstrated, especially in 

 Experiment 7, where the difference between —90° and +90° is distinctly 

 greater than that between — 70° and + 70°. Therefore, although the actual 

 permeabiUty is greater at 90°, and the turgor as a consequence less, than at 

 smaller angles with the vertical, the difference between the turgor of the upper 

 and under sides is greater and it is this differential permeability that produces 

 the curvature. This 'explains the stronger curvatures obtained with the root 

 horizontal. 



