ieu observes, that this genus
should still be retained amongst the Malpighiaceae. 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 {418} 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 aerating 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
{419} 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 affinities.
Nothing can be easier than to define a