genus should still be retained amongst the Malpighiace . This case
seems to me well to illustrate the spirit with which our
classifications are sometimes necessarily founded.
Practically when naturalists are at work, they do
not trouble themselves about the physiological value of the characters
which they use in defining a group, or in allocating any particular
species. If they find a character nearly uniform, and common to a great
number of forms, and not common to others, they use it as one of high
value; if common to some lesser number, they use it as of subordinate
value. This principle has been broadly confessed by some naturalists to
be the true one; and by none more clearly than by that excellent
botanist, Aug. St. Hilaire. If certain characters are always found
correlated with others, though no apparent bond of connexion can be
discovered between them, especial value is set on them. As in most
groups of animals, important organs, such as those for propelling the
blood, or for rating it, or those for propagating the race, are found
nearly uniform, they are considered as highly serviceable in
classification; but in some groups of animals all these, the most
important vital organs, are found to offer characters of quite
subordinate value.
We can see why characters derived from the embryo should be of equal
importance with those derived from the adult, for our classifications
of course include all ages of each species. But it is by no means
obvious, on the ordinary view, why the structure of the embryo should
be more important for this purpose than that of the adult, which alone
plays its full part in the economy of nature. Yet it has been strongly
urged by those great naturalists, Milne Edwards and Agassiz, that
embryonic characters are the most important of any in the
classification of animals; and this doctrine has very generally been
admitted as true. The same fact holds good with flowering plants, of
which the two main divisions have been founded on characters derived
from the embryo, on the number and position of the embryonic
leaves or cotyledons, and on the mode of development of the plumule and
radicle. In our discussion on embryology, we shall see why such
characters are so valuable, on the view of classification tacitly
including the idea of descent.
Our classifications are often plainly influenced by chains of
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