aced in an extremely dry, lofty conservatory, where, after some
years, instead of producing single flowers, they all produced double
ones. The seedlings and mother plant were planted in one and the same
kind of earth, and some of the flowers on the old plant also showed an
inclination to become double.

"This, at that time, to us, enigmatical phenomenon, was kept in mind
until we had an opportunity of instituting comparisons between the
climate of Japan and China and our own, and we then concluded that in
the case of a plant imported from thence, and exposed to such different
climatical influences, the origin of the greater or less imperfection of
its sexual organs was probably owing to this change, as we had
experienced in _Kerria_ and _Camellia_; and that the sterility of many
other exotic plants might be attributed to the same cause. The
difference in the climatical relations of Japan and Europe is very
considerable. In Japan, previous to the new growth of _Kerria_ and
_Camellia_, a rainy season of three months' duration prevails; in
Europe, on the contrary, dry winds prevail especially in the eastern
part, where our plains are often transformed into deserts. Is it,
therefore, remarkable that a plant introduced from Japan into Europe,
exposed to the influences of this great diversity of climate, should
produce imperfect sexual organs incapable of further propagating the
plant from seeds? A rich soil, with the necessary amount of moisture,
will never engender double flowers."[567]

Mr. Darwin[568] describes a peculiar form of _Gentiana Amarella_, in
which the parts of the flower were more or less replaced by compact
aggregations of purple scales in great numbers. A similar condition is,
indeed, not uncommon in this plant, and, as Mr. Darwin also remarked, on
hard, dry, bare, chalky banks, thus bearing out the views expressed by
the writer in the 'Gartenzeitung' just cited. Some double flowers of
_Potentilla reptans_ found growing wild near York, and transmitted to
the writer by a correspondent, were observed growing along a high wall,
in a dry border, close to a beaten path, bordering on a gravel pit,
others were found on a raised bank, which, from its elevation and
exposure to the sun, was particularly dry.

On the other hand, the double-flowered _Cardamine pratensis_, which is
occasionally found in a wild state, always grows in very wet places.

Of late years a remarkable double-flowered race of _Primula sinensis