Transpiration and the Ascent of Water in Trees 
under Australian Conditions. 
BY 
ALFRED J. EWART, D.Sc., Ph.D., F.L.S., 
Government Botanist and Professor of Botany in Melbourne University ; 
AND 
BERTHA REES, 
Government Research Bursar, Melbourne University . 
With five Figures in the Text. 
I N two previous papers 1 on the ascent of water in trees, investigations 
were made in regard to the physics of the ascent of sap, and from the 
data thus obtained experiments were performed to test whether any of the 
existing theories afforded a complete explanation of all the phenomena 
associated with the ascent of sap in tall trees. The net result of the 
previous work has been to show that the problem is more a kinetic 
than a static one, the actual resistance to flow during active transpiration 
being much greater than might be imagined from purely theoretical 
considerations. In addition it was shown that no evidence could be 
obtained of any pressure or suction at a given point sufficient to explain 
the total ascent in a tall tree during active transpiration, and that in the 
wood of a tree killed by formalin the sap appeared to turn to the older, 
still living wood, which normally, owing to its higher resistance and lesser 
activity, takes little or no part in the ascent of sap. The mere fact that 
dead wood soon loses its conductivity and cannot retain it permanently 
under transpiration conditions, even after injection with water, is sufficient 
to show that in this respect at least the ascent of sap is a vital problem, 
that is to say, one which cannot at present be wholly explained by reference 
to known physical and chemical agencies. All the data on which these 
conclusions were based were, however, obtained in England with English 
or English-grown trees, and naturally the opportunity of checking all the 
conditions in Australia, where the tallest trees grow, and where the 
1 Phil. Trans. R.S. of London, Series 13, vol. cxcviii, 1905 , p. 41 ; Ibicl., vol. cxcix, 1908 , p. 341 . 
[Annals of Botany, Vol. XXIV. No. XCIII. January, 1910.J 
