Grafts et al. 



130 



Water in Plants 



growth. In this respect it differs from mature tissues, for example that of 

 apple fruit parenchyma, where further growth is not normal. 



60 



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Fig. 39. — Effect of auxiss on water uptake of potato tissue 

 under sterile and non-sterile conditions. The height of the bars 

 extending above the dotted line indicates the auxin-induced water 

 uptake of the sterile cultures. A. Experiment in water and 1 and 

 10 mg per liter naphthaleneacetic acid. Duration of test, 4 days. 

 B. Test carried out at same time and with same material as A; 

 0.2 M mannitol used as basic medium. C. Test similar to A and 

 B, but made at a different time; 0.2 M sucrose used as basic 

 medium, and 1, 10, and 100 mg per liter indoleacetic acid as auxin. 

 Data of VAN Overbeek (1944). 



It is evident that at least in some instances the phenomena are not due 

 to solute accumulation. To say that auxin accelerates the respiratory rate 

 carries little meaning without knowing how the extra energy output is 

 related to water retention. If the auxin effect is one of increasing wall 

 plasticity only, it is clear that no swelling could take place in hypertonic 

 solution. The fact that expressed sap is slightly more dilute for the auxin- 

 treated discs (van Overbeek) is still not conclusive evidence that the 

 vacuolar OP did not increase, due to the possibility of active uptake of 

 water by the protoplasm. Data on this point would be helpful. 



