The flower itself undergoes a parallel modification due to a similar
cause. It is formed by a series of modified leaves arranged round a
shortened axis. In its earlier stages the number of these modified
leaves is indefinite, as in many Ranunculaceae; and the axis itself is
not greatly shortened, as in Myosurus. The first advance is to a
definite number of parts and a permanently shortened axis, in the
arrangement termed hypogynous, in which all the whorls are quite
distinct from each other. In the next stage there is a further
shortening of the central axis, leaving the outer portion as a ring on
which the petals are inserted, producing the arrangement termed
perigynous. A still further advance is made by the contraction of the
axis, so as to leave the central part forming the ovary quite below the
flower, which is then termed epigynous.

These several modifications are said to be parallel and definite, and to
be determined by the continuous checking of vegetation by reproduction
along what is an absolute groove of progressive change. This being the
case, the importance of natural selection is greatly diminished. Instead
of selecting and accumulating spontaneous indefinite variations, its
function is to retard them after the stage of maximum utility has been
independently reached. The same simple conception is said to unlock
innumerable problems of vegetable morphology, large and small alike. It
explains the inevitable development of gymnosperm into angiosperm by the
checked vegetative growth of the ovule-bearing leaf or carpel; while
such minor adaptations as the splitting fruit of the geranium or the
cupped stigma of the pansy, can be no longer looked upon as achievements
of natural selection, but must be regarded as naturally traceable to
the vegetative checking of their respective types of leaf organ. Again,
a detailed examination of spiny plants practically excludes the
hypothesis of mammalian selection altogether, and shows spines to arise
as an expression of the diminishing vegetativeness--in fact, the ebbing
vitality of a species.[209]

_Objections to the Theory._

The theory here sketched out is enticing, and at first sight seems
calculated to throw much light on the history of plant development; but
on further consideration, it seems wanting in definiteness, while it is
beset with difficulties at every step. Take first the shortening of the
raceme into the umbel and the capitulum, said to be caused by