146 LAWS OF VAEIATION. Chap. V. 
these two orders^ is so far-fetched, as it may at first 
appear: and if it be advantageous, natural selection 
may have come into play. But in regard to the differ¬ 
ences both in the internal and external structure of the 
seeds, which are not always correlated with any differ¬ 
ences in the flowers, it seems impossible that they can 
be in any way advantageous to the plant: yet in the 
Umbellifer86 these differences are of such apparent im¬ 
portance—the seeds being in some cases, according to 
Tausch, orthospermous in the exterior flowers and coe- 
lospermous in the central flowers,—that the elder De 
Candolle founded his main divisions of the order on 
analogous differences. Hence we see that modifica¬ 
tions of structure, viewed by system atists as of high 
value, may be wholly due to unknown laws of correlated 
growth, and without being, as far as w^e 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 in¬ 
dependent 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 ex¬ 
plain 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 , 
