86 
Ewart and Rees .— Transpiration and the Ascent of 
conditions are in some respects almost unique, and with abundant material 
close at hand, was of great value. The work was carried out with the aid 
of a grant by the Royal Society from the Home Government’s research 
fund. 
The points of special importance to determine were : the rate of tran¬ 
spiration under Australian conditions, the rate of ascent of sap, more 
especially in Eucalyptus trees, the length and diameter of the vessels, 
the condition of the conducting tissue during active transpiration, and the 
maximal and average resistances to flow in functioning stems. The total 
resistance to flow naturally will depend on the height of the tree, and the 
tallest trees known only slightly exceed 300 feet in height. In the previous 
paper the greatest height given for Eucalyptus amygdalina was 303 feet. 
I have since found an authentic properly measured record of 330 feet by 
Mr. Clement Hodgkinson, a former head of the Lands Department, taken 
nearly half a century ago, and although the tree does not now appear to 
be in existence, there is no reason to doubt the record. 1 As regards this 
genus, Eucalyptus diversicolor of W. Australia appears to come second, and 
the Eucalyptus microcorys of N.S. Wales third in height, but many species 
are often found to attain heights of 100 to 200 feet in the heavily timbered 
districts of Victoria, although the trunks are usually slender as compared 
with the height. A tree, however, commonly continues to grow in diameter 
after it has attained its maximal height, and hence in aged specimens the 
disparity between the diameter and height is reduced. The next tallest 
tree recorded is presumably the ‘ Keystone State ’ Sequoia of Calaveras 
with 325 feet in height and 45 feet in diameter. The Sequoias appear 
in general to have bulkier stems for a given height than Eucalyptus , and 
this, coupled with the slower rate of transpiration, makes up for the com¬ 
paratively high resistance to flow in their non-vascular wood. In fact, 
as has already been shown, 2 the development of wood on a tree is primarily 
due to the necessity of maintaining a sufficient sectional area of wood 
containing living cells, and hence capable of active conduction, the purely 
mechanical functions of the stem being secondary in character ; the main 
stem of a tree which has attained its maximal height will continue to increase 
in girth and strength even although the upper half may be decreasing in 
weight. 
Transpiration under Australian Conditions. 
In at least one respect the Australian conditions as represented in the 
Melbourne district are comparatively unique, for at certain times hot dry 
winds blow from the interior and cause rapid rises of temperature up to ioo° 
1 Dr. Hovvitt, in the Proc. Roy. Soc. of Viet., New Series, vol. iii, 1891 , p. 128 , gives a measure¬ 
ment of 350 feet on a fallen Eucalypt, but without details and without mentioning whether the 
measurement included any portion of the root system. 
2 Phil. Trans. R.S., Series 13, vol. cxcviii, 1905 , p. 69 . 
