Grafts et al. 



128 — 



Water in Plants 



aerated distilled water and to oxygen-free distilled water. A definite tem- 

 perature effect was observed. As an example, the increase in fresh weight 

 of discs kept in aerated water for two days at 21° C. amounted to 10.3 per 

 cent, compared to 4.7 per cent for a temperature of 10-11° C. In another 

 experiment, carried out at 21° C. and 1-2° C, the respective amounts were 

 11.3 and 1.6 per cent for the same period of time. Addition of heteroauxin 

 produced a much greater increase in wet weight, and resulted in a greater 

 loss of dry weight. Aeration of the bathing solution induced cell divisions 

 and disappearance of starch from the surface region of the tissue disc. No 

 cell divisions were observed in unaerated cultures. The conclusion of the 

 author is that the auxin effect is on respiration itself, and that the addi- 

 tional energy released is somehow utilized in uptake of water. 



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Fig 38.— The effect of 0.2 M sucrose (S), 0.2 M sucrose plus 10 mgm. of indole- 

 3-acetic acid per liter (SA), these concentrations of sucrose and auxin plus 10 3 M. 

 KCl (SAK), these concentrations of sucrose and auxin plus 10-4 M. K fumarate 

 (SAF) on changes in the wet weight of aerated potato slices. Data of Commoner, 

 FOGEL, and Muller (1943). 



Steward, Stout and Preston (1940) were unable to concur that 

 Reinders' data proved water uptake to be an active process in potato tissue, 

 because respiration was measured only by loss of dry weight. In their 

 opinion the fact that auxin induces an influx of water into the tissue is no 

 proof that the mechanism is not one of simple osmosis. 



Steward and his collaborators however report data which do support 

 the possibility of active water absorption by potato in the absence of added 

 auxin. Discs placed in aerated 0.005 N solutions of KBr and KNO3 

 showed increases in fresh weight surpassing those of discs in distilled 

 water. A specific effect of the ions involved was suggested as a possible 

 explanation. Whereas potassium increased water absorption, calcium acted 

 as an inhibitor. The effect of potassium ion was increased when accom- 

 panied by nitrate ion. 



