e next most
important, because the seed is the main reliance for new plants. The
part next in importance is the leaf and that we will now study.

If you will go into the field and observe the leaves on a number of
plants, you will find that the following facts are true:

They are all green.

They are flat and thin.

Many of them are very broad.

Some of the leaves on a single branch are larger than others on the
same branch, and some have longer stems than others.

Most of them have a rather dark glossy upper surface and a lighter
rougher under surface.

[Illustration: FIG. 59.
To show transpiration. Plant _A_ was set in the sunlight, plant _B_
was left in the darker part of the room. _A_ has transpired much more
than _B_, showing that sunlight is necessary for this work.]

[Illustration: FIG. 60.--AMOUNT OF TRANSPIRATION
This plant transpired within 48 hours an amount of water equal to the
colored liquid in the bottle standing on the jar, more than 6 ounces.]

The leaves on the lower branches of the trees are spread out in a more
or less flat layer and have their glossy surfaces all turned up,
while those on branches in the tops of trees or shrubs are arranged
all around the branch, the glossy surface being turned up.

What are the reasons for these facts?

A study of the work of the leaves and the conditions necessary for
them to perform their work will help us to answer this question.

THE USES OF LEAVES TO PLANTS

=Experiment.=--(See Fig. 59). Take a pot or tumbler in which a young
plant is growing, also a piece of pasteboard large enough to cover the
top of the pot; cut a slit from the edge to the centre of the
pasteboard, then place it on the top of the pot, letting the plant
enter the slit. Now close the slit with wax or tallow, making it
perfectly tight about the stem. If the plant is not too large, invert
a tumbler over it, letting the edge of the tumbler rest on the
pasteboard; if a tumbler is not large enough use a glass jar. If a
potted plant is not convenient a slip or a seedling bean or pea placed
in a tumbler of water will serve the purpose. Prepare several and
place some in a sunny window and leave others in the room where it is
darker, and observe them from time to time. In the case of those
plants that were set in the sunny window moisture will be seen
collecting on the inner surface of the tumbler. Where does this come
from? It is absorbed from the soil by the roots and is sent with