e period of vegetation, and the ripening
of the seed, would have been thus affected; but it is a much more
surprising fact that the seeds should have undergone so rapid and great a
change. As, however, flowers, with their product the seed, are formed by
the metamorphosis of the stem and leaves, any modification in these latter
organs would be apt to extend, through correlation, to the organs of
fructification.

_Cabbage_ (_Brassica oleracea_).--Every one knows how greatly the
various kinds of cabbage differ in appearance. In the island of Jersey,
from the effects of particular culture and of climate, a stalk has
grown to the height of sixteen feet, and "had its spring shoots at the
top occupied by a magpie's nest:" the woody stems are not unfrequently
from ten to twelve feet in height, and are there used as rafters[579]
and as walking-sticks. We are thus reminded that in certain countries
plants belonging to the generally herbaceous order of the Cruciferae are
developed into trees. Every one can appreciate the difference between
green or red cabbages with great single heads; Brussel-sprouts with
numerous little heads; broccolis and cauliflowers with the greater
number of their flowers in an aborted condition, incapable of producing
seed, and borne in a dense corymb instead of an open panicle; savoys
with their blistered and wrinkled leaves; and borecoles and kales,
which come nearest to the wild parent-form. There are also various
frizzled and laciniated kinds, some of such beautiful colours that
Vilmorin in his Catalogue of 1851 enumerates ten varieties, valued
solely for ornament, which are propagated by seed. Some kinds are less
commonly known, such as the Portuguese Couve Tronchuda, with the ribs
of its leaves greatly thickened; and the Kohlrabi or choux-raves, with
their stems enlarged into great turnip-like masses above the ground;
and the recently formed new race[580] of choux-raves, already including
nine sub-varieties, in which the enlarged part lies beneath the ground
like a turnip.

Although we see such great differences in the shape, size, colour,
arrangement, and manner of growth of the leaves and stem, and of the
flower-stems in the broccoli and cauliflower, it is remarkable that the
flowers themselves, the seed-pods, and seeds, present extremely slight
differences or none at all.[581] I comp