650 Report of a Discussion on 
by Professor Askenasy as representing his views. I have here a 
type-written copy of our original manuscript, and the original is in 
the possession of the Royal Society and doubtless quite accessible. 
Reference to either will show that the sentence which Professor 
Askenasy quotes as representing his views on the matter occurs in 
our original manuscript, and was published from it without change of 
a syllable. The priority, for what is, at most, but a shade of meaning, 
is thus given away by his own decision. 
After what I have quoted from Professor Askenasy as to imbibition- 
force of the cell-wall being ‘ the so long vainly sought for source of 
the suction-force concerned in the ascent of sap in the plant/ it will 
perhaps appear surprising that Mr. Darwin interprets Professor Aske- 
nasy as advancing the view ‘ that the tractional force is supplied by the 
osmotic suck of the leaves ’ ; and, taking this view, dismisses Dixon’s 
paper of 1896 1 as a reversion by Dixon to Professor Askenasy’ s views 
of 1895. The quotation from Professor Askenasy which I have given 
above is, indeed, from his second paper; but in his 1895 paper we find 
Professor Askenasy asking leave to modify a statement that osmotic 
forces are responsible, when he recalls how in dead trees the imbi- 
bition force alone can accomplish this, and proceeds to quote at 
a length of several pages experimental evidence in support of this 
view. Professor Askenasy does indeed refer to osmotic force as 
active in transferring the sap from the bundles into the cells of the 
leaf ; but we ourselves, in our original paper, suggest as probable that 
this action occurs. In dwelling upon the great importance of osmotic 
pressure, Dixon advances alike beyond the views contained in our 
original paper and those put forth by Professor Askenasy. As will 
be seen presently, for the explanation of the active lifting forces in the 
leaf, we have not to go beyond our original statements that this is 
referable to the phenomena of evaporation in the leaf so far as our 
knowledge definitely extends 2 . 
1 Note on the Role of Osmosis in Transpiration, Proc. Royal Irish Academy, 
January, 1896. 
2 ‘ Although osmotic actions may be concerned with the evaporative functions 
of the leaf, i. e. in the transference of water into the protoplasm-filled cells ; still 
it is very probable that surface-tension forces developed upon the surfaces of walls 
coming in direct contact with air diffusion currents are responsible principally for 
the tensile forces displayed by the leaf. The fact that transpiration is not only 
accelerated by direct sunshine, but even more influenced by warm dry winds, 
supports the view that evolution of vapour at the leaf obeys the general laws 
