94 



P.E. WEATHERLEY 



2-2 



^2-0 

 a 1-8 



D 

 UJ 



I 







ttO-8 

 gO.6 



\ 



1-4 



1'2- 



0-4, 



2 5-2 9 C 



O 10 20 



Ihr. 



22-6"'C 



fX- 



\< 



O 10 20 30 40 50 

 TIME (MINUTES) 



2 3 4 



TIME (HOURS) 



Fig. 5. A: The effect of temperature on uptake into the inner and outer spaces. Trans- 

 piration was stopped by immersion in water below 3°C. The first phase of the die-away 

 proceeded normally for 22 minutes (i.e. into the outer space). Thereafter there was no 

 uptake for i hour. Only an immersion in water at 22-6°C was the second phase of 

 uptake able to proceed (i.e. into the inner space) . B : The effect of lowering the tempera- 

 ture on the flux of water through a tomato root system with the continuous application 

 of a pressure difference of 2 atm across the cortex. (Redrawn from Jackson and 

 Weatherley, 1962.) 



III. MOVEMENT ACROSS THE ROOT CO RTEX 



Here, entirely different methods were used. In essence these were based 

 on the following concept. If a permeable barrier permits only diffusional 

 passage of water, then equivalent osmotic and pressure gradients will 

 result in an equal flux of water. If on the other hand mass flow can occur 



