into the air and those where they remain in the ground.

_In the Air_. _In the Ground_.

Bean. Almond. Squash. Acorn. Horsechestnut.
Pea. Nasturtium.

In the latter the cotyledons are so heavily gorged with nourishment that
they never become of any use as leaves. As Darwin points out, they have
a better chance of escaping destruction by animals by remaining in the
ground.

The cotyledons are very good illustrations of the different uses to which
a single organ may be put, and the thorough understanding of it will
prepare the pupils' minds for other metamorphoses, and for the theory that
all the various parts of a plant are modified forms of a very few members.


4. _Nature of the Caulicle_.--Probably some of the pupils will have called
the caulicle the root. It is, however, of the nature of stem. The root
grows only at the end, from a point just behind the tip; the stem
elongates throughout its whole length. This can be shown by marking the
stem and roots of a young seedling with ink. India ink must be used, as
common ink injures the plants. Dip a needle in the ink and prick a row
of spots at equal distances on a young root. Corn is very good for this
purpose, but Morning-Glory or Bean is better for experiments on the
stem. The plants should then be carefully watched and the changes in
the relative distance of the spots noted. The experiment is very easily
conducted with the seedlings growing on sponge, with their roots in the
moist air of the tumbler, as before described.