THE PATHWAY OF WATER MOVEMENT 



91 



and the water supplied at the cut end of petiole. On this interpretation the 

 initial steep fall in Fig. 4B represents the die-away in uptake by the pathway 

 (outer space of the cells, e.g. cell walls) and the subsequent slower fall 

 represents the die-away in uptake by the inner space of the cells (vacuoles, 

 etc.). Now if we assume that the pattern of uptake by the inner space of 

 the cells was uniform throughout, its die-away curve during the first 10 



RESERVOIR 



TAP 



VALVE RUBBER 



-■C 



Fig. 3. Simple potometer showing method of attachment of leaf. Transpiration could 

 be stopped suddenly by raising the beaker to submerge the leaf. 



minutes will be represented by the hne of extrapolation to ip and the line 

 pr represents the die-away in uptake by the inner space throughout the 

 experiment. Thus the rates of uptake by the inner space alone during the 

 first 20 minutes were obtained by taking antilogs of values lying along ;)^, 

 and by subtracting these rates of uptake from the experimental values 

 (total uptake) the rates of uptake by the pathway alone were obtained. 



Integrated curves showing the progressive saturation of the two spaces 

 in the leaf were obtained bv summation of the rates derived in the above 



