362 BOTANICAL GAZETTE [May 
An experiment was also made with three pinometers inserted into 
the stem of a fuchsia plant. The following readings were taken 
after the experiment had been going on for some time. The lower 
pinometer showed root pressure with a difference in the level of the 
mercury columns of 31™™, the middle pinometer showed suction 
with a difference in level of 85™™, and the upper. pinometer suction 
with a difference of 63.5"™. The figures for the next day in milli- 
meters were 39 (an increase of 8), 127.2 (42.2), and 128 (64.5) 
respectively. The two lower pinometers were below the lowest 
branches. In this case, therefore, root pressure could not be observed 
even up to the lowest lateral shoot. As in all the previous experi- 
ments, suction, where observed at all, was maintained day and 
night, till, owing to the pull on the cut surface of the plant, air made 
its appearance and the mercury returned to its original level. 
The pinometer, as described here, is meant to be of use chiefly 
for class and demonstration purposes. I wish now to point out what 
the results obtained by employing it.are, that is to say what obser- 
vations can be made on the transpiration stream. 
We can readily see that in our plants, at least, it isnevera function 
of the root to press water up into the leaves. By day and by night 
the phenomenon of root pressure can be observed only below the 
lowest shoot. But root pressure is an extremely useful if not a 
necessary process by which the rise of the water is started. Referring 
to those of our experiments in which the lower cut surface of the shoot 
was exposed to pressure, we see that the plants do not suffer much by 
the stem being cut across. It appears to be necessary that water should 
be forced into the lowest end of the vascular system; or at least 
there should be no pull on it. Root pressure, therefore, is not only a 
symptom of the avidity with which the roots are absorbing wateT, 
but it is of importance as assisting in the starting of the transpiration 
current. 
It must be mentioned here, however, that the insertion of a pino- 
meter into a fuchsia plant is in any case a serious thing for the latter- 
The phenomena of exudation and bleeding seem to cease entirely 
when the shoot has been severed from its connection with the root. 
This statement holds good whether the gauge of the pinometer shows 
pressure or suction. The fact that at different heights in the plant 
