the flowers, it seems impossible that they can be in any way
advantageous to the plant: yet in the Umbellifer these differences are
of such apparent importance the seeds being in some cases, according to
Tausch, orthospermous in the exterior flowers and coelospermous in the
central flowers, that the elder De Candolle founded his main divisions
of the order on analogous differences. Hence we see that modifications
of structure, viewed by systematists as of high value, may be wholly
due to unknown laws of correlated growth, and without being, as far as
we can see, of the slightest service to the species.
We may often falsely attribute to correlation of growth, structures
which are common to whole groups of species, and which in truth are
simply due to inheritance; for an ancient progenitor may have acquired
through natural selection some one modification in structure, and,
after thousands of generations, some other and independent
modification; and these two modifications, having been transmitted to a
whole group of descendants with diverse habits, would naturally be
thought to be correlated in some necessary manner. So, again, I do not
doubt that some apparent correlations, occurring throughout whole
orders, are entirely due to the manner alone in which natural selection
can act. For instance, Alph. De Candolle has remarked that winged seeds
are never found in fruits which do not open: I should explain the rule
by the fact that seeds could not gradually become winged through
natural selection, except in fruits which opened; so that the
individual plants producing
seeds which were a little better fitted to be wafted further, might get
an advantage over those producing seed less fitted for dispersal; and
this process could not possibly go on in fruit which did not open.
The elder Geoffroy and Goethe propounded, at about the same period,
their law of compensation or balancement of growth; or, as Goethe
expressed it, in order to spend on one side, nature is forced to
economise on the other side. I think this holds true to a certain
extent with our domestic productions: if nourishment flows to one part
or organ in excess, it rarely flows, at least in excess, to another
part; thus it is difficult to get a cow to give much milk and to fatten
readily. The same varieties of the cabbage do not yield abundant and
nutritious foliage and a copious supply of oil-bearing seeds. When the
seeds in our fruits become atrophied, the fruit itself gains largely in
size and quality. In our poultry, a large tuft of feathers on the head
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