will be the same. Fasten
the tube in this position and observe it frequently for three or
four hours. At the end of the time you should find that the
molasses in the tube has risen above the level of the liquid
outside. It may even overflow at the top. If you use the
lamp-chimney the rise will not be so clearly seen, since a greater
volume is required to fill the space in the chimney. This increase
in the contents of the tube is due to the entrance of water from
the outside. The water has passed through the thin bladder, or
membrane, and has come to occupy space in the tube. There is also a
passage the other way, but the molasses can pass through the
bladder membrane so slowly that the passage is scarcely noticeable.
There are no holes, or openings, in the membrane, but still there
is a free passage of liquids in both directions, although the more
heavily laden solution must move more slowly.

A root-hair acts in much the same way as the tube in our experiment,
with the exception that it is so made as to allow certain substances to
pass in only one direction, that is, toward the inside. The outside of
the root-hair is bathed in solutions rich in nourishment. The
nourishment passes from the outside to the inside through the delicate
membrane of the root-hair. Thus does food enter the plant-root. From the
root-hairs, foods are carried to the inside of the root.

From this you can see how important it is for a plant to have fine,
loose soil for its root-hairs; also how necessary is the water in the
soil, since the food can be used only when it is dissolved in water.

This passage of liquids from one side of a membrane to another is called
_osmosis_. It has many uses in the plant kingdom. We say a root takes
nourishment by osmosis.

SECTION X. ROOT-TUBERCLES

Tubercle is a big word, but you ought to know how to pronounce it and
what is meant by root-tubercles. We are going to tell you what a
root-tubercle is and something about its importance to agriculture. When
you have learned this, we are sure you will want to examine some plants
for yourself in order that you may see just what tubercles look like on
a real root.

Root-tubercles do not form on all kinds of plants that farmers grow.
They are formed only on those kinds that botanists call _legumes_. The
clovers, cowpeas, vetches, soy beans, and alfalfa are all legumes. The
tubercles are little