In certain Umbelliferae the
exterior seeds, according to Tausch, are orthospermous, and the central one
coelospermous, and this is a character which was considered by De Candolle
to be in other species of the highest systematic importance. Professor
Braun mentions a Fumariaceous genus, in which the flowers in the lower part
of the spike bear oval, ribbed, one-seeded nutlets; and in the upper part
of the spike, lanceolate, two-valved and two-seeded siliques. In these
several cases, with the exception of that of the well-developed ray-
florets, which are of service in making the flowers conspicuous to insects,
natural selection cannot, as far as we can judge, have come into play, or
only in a quite subordinate manner. All these modifications follow from
the relative position and inter-action of the parts; and it can hardly be
doubted that if all the flowers and leaves on the same plant had been
subjected to the same external and internal condition, as are the flowers
and leaves in certain positions, all would have been modified in the same
manner.
In numerous other cases we find modifications of structure, which are
considered by botanists to be generally of a highly important nature,
affecting only some of the flowers on the same plant, or occurring on
distinct plants, which grow close together under the same conditions. As
these variations seem of no special use to the plants, they cannot have
been influenced by natural selection.
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