AN APPARATUS FOR OBSERVING THE TRANSPIRATION 
STREAM. 
Otto V. DARBISHIRE, 
(WITH TWO FIGURES) 
THERE are, roughly speaking, two sets of experiments by means 
of which we can investigate the presence of the transpiration stream 
in small plants. One of these is concerned with the root of the plant 
and with the demonstration of the phenomenon known as root pres- 
sure. The other set deals with the shoot and the suction exerted 
by it on the water which is being absorbed by the root. 
We all know what happens when we fix some kind of root pressure 
apparatus to the stump of a small plant, like a fuchsia for example. 
Water will soon be pressed out of the stump with sufficient force to 
raise a column of mercury to a considerable height. We can at the 
same time attach to the shoot of the very plant used for the root 
pressure experiment some form of potometer. We will observe 
suction and a column of mercury can be raised to a considerable 
height thereby. Do these two separate experiments really—even 
approximately—show what was going on in the plant at the time 
the experiment was set up? I think the answer must be no. When 
the plant in question was cut across, the stump exhibited the phenom- 
enon of pressure, but the shoot that of suction at the same level. 
It is obviously impossible that pressure and suction should be exhib- 
ited by an intact plant at the same level. It must be mentioned here, 
however, that if the two experiments are set up very quickly, we may 
find the stump exhibiting suction for a short time. This changes 
to pressure when the stump is saturated with water. The root may 
of course become saturated in a few minutes by simply being exposed 
to water during the setting up of the experiment. We do not 
therefore get a clear idea of what is going on in the plant, when we 
isolate the shoot from the root, by attaching to each one a separate 
apparatus. r 
In order to learn more about the relation between shoot suction 
and root pressure it is obviously necessary not to separate the cea 
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