moisture gives out. If it is desired to continue this experiment some
time, a small hole should be cut in the pasteboard before it is
fastened to the jar. This hole is for adding water to the jar from
time to time. The hole should be kept closed with a cork. The amount
of water added should always be weighed and account taken of it in the
following weighings. While this plant is growing it will be well to
wrap the jar with paper to protect the roots from the light.

It has been found that the amount of water necessary to grow a plant
to maturity is equal to from 300 to 500 times the weight of the plant
when dry.

This gives us an idea of the very great importance of water to plants.

=Experiment.=--Take a few leaves from a plant of cotton, bean, clover
or other plant that has been growing in the sunlight; boil them for a
few minutes to soften the tissues, then place them in alcohol for a
day or until the green coloring matter is extracted by the alcohol.
Wash the leaves by taking them from the alcohol and putting them in a
tumbler of water. Then put them in saucers in a weak solution of
iodine. The leaf will be seen to gradually darken; this will continue
until it becomes dark purple or almost black (Fig. 61). We have
already learned that iodine turns starch this color, so we conclude
that leaves must contain starch. (Five or ten cents worth of tincture
of iodine from a drug store diluted to about the color of weak tea
will be sufficient for these leaf experiments.)

=Experiment.=--If a potted plant was used for the last experiment, set
it away in a dark closet after taking the leaves for the experiment. A
day or two after, take leaves from it before removing it from the