and break the skin of the egg just under the end of the tube. Fill the
bottle with water till it overflows, and set the egg on the bottle,
the large end in contact with the water (Fig. 14). In an hour or so
the contents of the egg will be seen rising in the glass tube. This
happens because the water is making its way by osmose into the egg
through the skin, which has no openings, so far as can be discovered.
If the bottle is kept supplied with water as fast as it is taken up by
the egg, almost the entire contents of the egg will be forced out of
the tube. In this way water in which plant food is dissolved enters
the slender root hairs and rises through the plant.

=Experiment.=--This process of osmose may also be shown as follows
(Fig. 15): Remove the shell from the large end of an egg without
breaking the skin, break a hole in the small end of the egg and empty
out the contents of the egg; rinse the shell with water. Fill a
wide-mouthed bottle with water colored with a few drops of red ink.
Fill the egg-shell partly full of clear water and set it on the bottle
of colored water. Colored water will gradually pass through the
membrane of the egg and color the water in the shell. Prepare another
egg in the same way, but put colored water in the shell and clear
water in the bottle. The colored water in the shell will pass through
the skin and color the water in the bottle. Sugar or salt may be used
in place of the red ink, and their presence after passing through the
membrane may be detected by taste.


CONDITIONS NECESSARY FOR ROOT GROWTH

We have learned some of the things that the roots do for plants and a
little about how the work is done. The next thing to find out is: