PLANT PHYSIOLOGY 127 
it must be noted that in this experiment we have 
nothing to represent the cytoplasm. Hence it does not 
quite demonstrate what happens in the living plant, 
where the cytoplasm exercises an influence on the 
quantity of the various salts absorbed, and also controls 
the exit of the cell-sap. But just as, in the experiment, 
the water passed into the thistle funnel more quickly 
than the solution passed out, so in the root-hairs water 
passes in more rapidly than out, until the cells are 
turgid. Apparently the cytoplasm then becomes per- 
meable, and sap is passed into the next cell until it also 
is turgid, and so on, until the water is forced into the 
wood-vessels of the root. It thus enters the vessels 
under pressure and will tend to rise upwards. This 
gives rise to what is known as “‘ root-pressure ”’, 
91. Experiment 3.—To show the force of root-pressure. 
Apparatus.—Glass and rubber tubing, young plant 
(Broad Bean, Dahlia, Geranium all give good results). 
Method.—Cut the stem of the plant off close to the 
soil and quickly fix the rubber and glass tubing to it, and 
fill the latter with water up to a certain mark (if pos- 
sible use thermometer tubing with fine bore). 
Result.—The water rises in the tube! 
Deduction.—It has been forced up by the root. It 
is not only in the root-hairs that osmosis takes place, 
but the water is passed from cell to cell by the same 
process until it reaches the vessels. Here it is forced 
upwards, partly. by root-pressure, and partly by the 
force of capillarity which causes water to ascend fine 
tubes, the finer the tubes the higher being the rise. 
‘92. Experiment 4.—To show the force of Capillarity. 
Apparatus.—Glass tubing of different bores, coloured 
water, beakers. 
