urprising, as he finds scarcely a grain of good pollen. The
common little _Ranunculus ficaria_ rarely, and some say never, bears
seed in England, France, or Switzerland; but in 1863 I observed seeds
on several plants growing near my house. According to M. Chatin, there
are two forms of this Ranunculus; and it is the bulbiferous form which
does not yield seed from producing no pollen.[435] Other cases {171}
analogous with the foregoing could be given; for instance, some kinds
of mosses and lichens have never been seen to fructify in France.

Some of these endemic and naturalised plants are probably rendered
sterile from excessive multiplication by buds, and their consequent
incapacity to produce and nourish seed. But the sterility of others
more probably depends on the peculiar conditions under which they live,
as in the case of the ivy in the northern parts of Europe, and of the
trees in the swamps of the United States; yet these plants must be in
some respects eminently well adapted for the stations which they
occupy, for they hold their places against a host of competitors.

Finally, when we reflect on the sterility which accompanies the doubling of
flowers,--the excessive development of fruit,--and a great increase in the
organs of vegetation, we must bear in mind that the whole effect has seldom
been caused at once. An incipient tendency is observed, and continued
selection completes the work, as is known to be the case with our double
flowers and best fruits. The view which seems the most probable, and which
connects together all the foregoing facts and brings them within our
present subject, is, that changed and unnatural conditions of life first
give a tendency to sterility; and in consequence of this, the organs of
reproduction being no longer able fully to perform their proper functions,
a supply of organised matter, not required for the development of the seed,
flows either into these same organs and renders them foliaceous, or into
the fruit, stems, tubers, &c., increasing their size and succulency. But I
am far from wishing to deny that there exists, independently of any
incipient sterility, an antagonism between the two forms of reproduction,
namely, by seed and by buds, when either is carried to an extreme degree.
That incipient sterility plays an important part in the doubling of
flowers, and in the other cases just specified, I infer chiefly from