General Physiology of Plants 



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Fig. 53. Graph showing the rates of water secretion of two 

 similar tomato roots over a period of 3$ days, one (above) against 

 uniform (atmospheric) pressure, the other (below) against imposed 

 pressures up to 90 lbs./sq. in. The diurnal rhythm with which 

 secretion proceeds is a striking characteristic of the behavior of 

 tissues of this sort. (From White, P. R. 1938. Am. J. Bot. 25: 

 226, fig. 6, 267.) 



