Now run the wire down the tube 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: 

What conditions are necessary for the root to do its work?

We know that a part of the work of the root is to penetrate the soil and hold the plant firmly in place.  Therefore, it needs a firm soil.

We know that the part of the root which penetrates the soil is tender and easily injured.  Therefore, for rapid growth the root needs a mellow soil.

We know that part of the work of the root is to take moisture from the soil.  Therefore, it needs a moist soil.

We know that part of the work of the root is to take food from the soil.  Therefore, it needs a soil well supplied with plant food.

We know that roots stop their work in cold weather.  Therefore, they need a warm soil.

Another condition needed by roots we will find out by experiment.