It is quite
impossible to state these groups of facts in a more simple way than by
the statement that the tendency to become red is almost generally
present, though latent in leaves and stems, and that it comes into
activity whenever a stimulus provokes it.
Now it must be granted that the energizing of such a propensity under
ordinary circumstances is quite another thing from the origination of a
positive variety by the evolution of the same character. In the variety
the activity has become independent of outer influences or dependent
upon them in a far lesser degree. The power of producing the red
pigments is shown to be latent by the facts given above, and we see that
in the variety it is no longer latent but is in perfect and lasting
activity throughout the whole life of the plant.
Red varieties of white flowers are much more rare. Here the latency of
the red pigment may be deduced partly from general arguments like those
just given, partly from the special systematic relations in the given
cases. Hildebrand has clearly worked out this mode of proof. He showed
by the critical examination of a large number of instances that the
occurrence of the red-flowered varieties is contingent upon the [241]
existence of red species in the same genus, or in some rare cases, in
nearly allied genera.
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