644 
Report of a Discussion on 
Professor Vines said : — 
It must, I think, have come as a surprise to many of the general 
public here present, that we are not yet in possession of a coherent 
theory as to the mode in which water is conveyed to the leaves from 
the roots of trees. It is almost incredible that though this problem 
has been the subject of research for more than a century, it still 
remains, as Mr. Darwin has pointed out, without its solution. But 
after the admirable account of the history of the subject to which we 
have been listening, there is no occasion for me to say anything about 
the past. My object in taking part in this discussion is to give some 
account of observations which I have been recently making, in the 
endeavour to carry the subject a step further onwards. 
The particular feature of the problem which seemed to me to 
specially call for investigation is what is termed the suction-force of 
branches. I may explain what I mean by suction-force by referring 
to an experiment which has, I feel sure, been performed by every one 
in this room. When a gathered flower is placed in a glass of water, 
it sucks up a certain amount of the liquid ; and it does so with 
a certain force, as can be proved by appropriate means : this force is 
the suction-force of the flower. Many have already measured the 
suction-force of various branches, &c., but it does not appear to me 
to have been done so systematically as to afford any important body 
of evidence on the subject. With this end in view, I have devised an 
apparatus 1 which combines simplicity with sensitiveness. I may 
briefly describe it as a system of tubes, partly glass, partly thick india- 
rubber pressure-tubing, completely filled with water, connected air- 
tight on the one hand with the branch under experiment, and on the 
other with a Bourdon’s vacuum-gauge : the readings on the dial of 
the gauge are in inches of mercury, and indicate the suction-force 
exerted by the branch. I thought at first that I had succeeded in 
devising an apparatus which possessed the special advantage that 
it indicated suction-force without the intervention of atmospheric 
pressure, and that therefore my results were different in kind from 
those of previous observers. I am glad to have this opportunity 
of distinctly stating that I was mistaken in this conclusion : as a matter 
of fact, the atmospheric pressure does contribute to the readings given 
on the dial. I was misled by the fact that the readings of the gauge 
are due to the withdrawal of very small quantities of water ; so small, 
1 Described and figured in Annals of Botany, Vol. x, No. 39, September, 1896. 
