[Footnote 1: Reader in Botany. III. Seed-Food.]
Also the questions have brought out the fact that the Bean and Pea have the plumule ready formed in the seed, while the Morning-Glory and Sunflower have not. Why should this be? It is because there is so much food stored in the first two that the plumule can develop before a root is formed, while in the others there is only nourishment sufficient to enable the plantlet to form its roots. These must make the second leaves by their own labor.
3. Comparison with other Dicotyledons.—The pupils should now have other seeds to compare with these four. Let them arrange Flax, Four o-clock, Horsechestnut, Almond, Nasturtium, Maple-seeds, etc., under two heads.
| Seeds with the Food stored outside the plantlet (Albuminous) | Seeds with the Food stored in the embryo itself (Exalbuminous) |
| Flax. Four-o'clock. Morning-Glory. | Acorn. Horsechestnut. Almond. Maple. Sunflower. Squash. Bean. Pea. Nasturtium. |
They may also be divided into those with and without the plumule.
| Without Plumule | With Plumule |
| Flax. Maple. Sunflower. Four-o'clock. Morning-Glory. | Acorn. Horsechestnut. Almond. Bean. Pea. Squash. Nasturtium. |
Those with plumules will be seen to have the most abundant nourishment. In many cases this is made use of by man.
These last can be again divided into those in which the cotyledons come up 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.