In other varieties the ribs of the leaves are thickened so as to
become themselves a culinary vegetable; while, in the Kohlrabi, the stem
grows into a turnip-like mass just above ground. Now all these
extraordinarily distinct plants come from one original species which
still grows wild on our coasts; and it must have varied in all these
directions, otherwise variations could not have been accumulated to the
extent we now see them. The flowers and seeds of all these plants have
remained nearly stationary, because no attempt has been made to
accumulate the slight variations that no doubt occur in them.
If now we turn to another set of plants, the turnips, radishes, carrots,
and potatoes, we find that the roots or underground tubers have been
wonderfully enlarged and improved, and also altered in shape and colour,
while the stems, leaves, flowers, and fruits have remained almost
unchanged. In the various kinds of peas and beans it is the pod or fruit
and the seed that has been subjected to selection, and therefore greatly
modified; and it is here very important to notice that while all these
plants have undergone cultivation in a great variety of soils and
climates, with different manures and under different systems, yet the
flowers have remained but little altered, those of the broad bean, the
scarlet-runner, and the garden-pea, being nearly the same in all the
varieties.
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