

THE WORK OF PLANTS 
height of the water in the tube 
should be made several times a day 
for several days. It will be found 
that the column rises and falls, show- 
ing that there 1s some fluctuation in 
the pressure from the roots. 
Thus we see that the roots by their 
absorptive power are capable, not 
only of taking in water from the soil 
with considerable force, but also of 
lifting it up to a considerable height. 
inthe stem. Root pressure, however, 
cannot lift the water to the tops of 
tall trees. It has been found that 
the root pressure of the birch can litt 
water 84.7 feet high, the grapevine 
36.5 feet, and the nettle 15 feet. 
A simple experiment to illustrate 


how root pressure works. Here is an 
experiment, easy to perform, which 
illustrates very well the way the root 
works in lifting water. Take a thistle 
tube (Fig. 127) and fill with a strong 
sugar solution. Tie tightly over the 
a large o 1 der I 
Fic. 126. The experiment 8 Peo end ss P 1ece of ah blad 
in operation showing 
aii alte in tb clase 1 Get one sheep’s bladder, or several, at the 
tube, butcher’s and remove the surplus meat, Inflate, 
