ffer in their
inner and outer flowers. It might have been thought that the development
of the ray-petals, by drawing nourishment from the reproductive organs
causes their abortion; but this can hardly be the sole case, for in some
Compositae the seeds of the outer and inner florets differ, without any
difference in the corolla. Possibly these several differences may be
connected with the different flow of nutriment towards the central and
external flowers. We know, at least, that with irregular flowers those
nearest to the axis are most subject to peloria, that is to become
abnormally symmetrical. I may add, as an instance of this fact, and as
a striking case of correlation, that in many pelargoniums the two upper
petals in the central flower of the truss often lose their patches
of darker colour; and when this occurs, the adherent nectary is quite
aborted, the central flower thus becoming peloric or regular. When the
colour is absent from only one of the two upper petals, the nectary is
not quite aborted but is much shortened.

With respect to the development of the corolla, Sprengel's idea that
the ray-florets serve to attract insects, whose agency is highly
advantageous, or necessary for the fertilisation of these plants, is
highly probable; and if so, natural selection may have come into
play. But with respect to the seeds, it seems impossible that their
differences in shape, which are not always correlated with any
difference in the corolla, can be in any way beneficial; yet in the
Umbelliferae these differences are of such apparent importance--the
seeds being sometimes orthospermous in the exterior flowers and
coelospermous in the central flowers--that the elder De Candolle founded
his main divisions in the order on such characters. Hence modifications
of structure, viewed by systematists as of high value, may be wholly due
to the laws of variation and correlation, without being, as far as we
can judge, of the slightest service to the species.

We may often falsely attribute to correlated variation 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