Dixon — Note on the Role of Osmosis in Transpiration. 11 o 



column of water depending from them, while the bladder has no such 

 tendency to collapse and corresponds to the evaporating cells of the 

 leaf. 



In this apparatus it is evident if the turgescence of the bladder 

 were removed either by destroying the osmotic properties of the 

 semipermeable membrane in the walls of the pot, or by supplying an 

 isotonic solution to the lower end of the tube, and if no change was 

 introduced altering the porosity of the membrane, that evaporation from 

 the collapsed bladder would still maintain a feeble current upwards in 

 the tube similar to the upward current in branches, the leaves of which 

 have lost their turgescence. 



In addition to the tension set up in the manner described by the 

 osmotic cells of the leaves in the water-conducting system of plants, it 

 seems very probable that under all circumstances the cells of the 

 medullary rays must draw the water needed in their metabolism by 

 their osmotic properties from the water conduits ; for these cells are 

 not connected directly with any large evaporating surfaces, and conse- 

 quently cannot depend on the tensile force which might be generated 

 by such evaporation to procure for them fresh supplies of water. 



In conclusion, I wish to thank Dr. J. Joly, Trinity College, Dublin, 

 for many valuable suggestions in writing this Paper. 



K.r.A. PROC, SKlf. 111., VOL. TIT. 3 F 



