ROOTS. 
dT 
covers the inner surface of the cell-wall of the root-hair. 
When the student has learned how 
active a substance proto- 
plasm often shows itself to be, he will not be astonished to find 
it behaving almost as though it were possessed of intelligence 
and will. Traveling by osmotic action 
eurrent of water derived from the 
up through the roots and into the 
contents of the egg was forced up into 
Fig. 21. 
56. Root Pressure. — The force 
ward flowing current of water presses 
by attaching a mercury gauge to 
the root of a tree, or the stem of 
a small sapling. This is best done 
in early spring after the thawing of 
the ground, but before the leaves 
have appeared. In Fig. 22 the ap- 
paratus is shown attached to the 
stem of adahlia. The large glass 
tube W, filled with mercury up to 
the level g and with water from g 
to near s, is fastened tightly to the 
cut stem ats. As water absorbed 
by the roots is forced over into W, 
the mercury level.in Q will rise 
higher and the difference of level 
in the two mercury-columns will 
measure the root pressure. For 
every foot of difference in level 
there must be a pressure of nearly 
six pounds per square inch on the 
stump at the base of the tube g. 
A black-bireh root tested in this 
from cell to cell, a 
root-hairs is forced 
stem, just as the 
the tube shown in 
with which the up- 
may be estimated 
Fic. 22. Apparatus for Measure- 
ment of Root Pressure. 
s, cut-off stem of dahlia; c, a piece 
of rubber tubing slipped over the 
stump s and the glass tube g and 
tied fast ; g, bent glass tube; W, 
water (sap forced up by the 
roots); Q,mereury-column sus- 
tained by the root pressure. 
way at the end of April 
has given a root pressure of 37 pounds to the square inch. 
This would sustain a column of water about 86 feet high. 
