THE PATHWAY OF WATER MOVEMENT 



97 



(Data from Mees and Weatherley, 1957) 



almost 90"/o inhibition whereas kp-ko only 20% in one experiment and 

 about 60% in another. 



One of the most striking features of these results was the demonstration 

 of a several fold increase in k^ following a rise in pressure of about 2 atm. 

 This constitutes a direct confirmation of the conclusions of Brewig 

 (1936-39) and Brouwer (1953-54) who worked with whole transpiring 

 plants. Significant though this may be in indicating that transpirational 

 tensions reduce the resistance of roots to osmotic water flux, it hardly 

 clarifies the complex picture of water movement through the root for the 

 mechanism of this change in permeabihty is as yet unknown. In view of the 

 insensitivity of the transpiration pathway in the leaf to low temperature it is 

 noteworthy that flux through the root is not only sensitive to metabohc 

 inhibitors as shown above but is also greatly reduced by lowering the 

 temperature (see Fig. 5B). Evidently metabolic activity is necessary to 'keep 



Table 2 

 The effect of cyanide on the osmotic and pressure permeability coefficients 



(Data from Mees and Weatherley, 1957) 



