ercised by
the organs implicated--points beyond the scope of the present volume.

=Teratology and classification.=--Lastly, there remain to be mentioned
the bearings of teratology on systematic botany. There are those who
would entirely exclude teratology from such matters. It may be expedient
to do so when the object sought is one of convenience and facility of
determination only, but when broader considerations are concerned,
teratology must no more be banished than variation. In most instances
the one differs but in degree from the other. If variation affords aid
in our speculations as to the affinities and genealogical descent of
species and other groups, so does teratology, and in a far higher
degree.

Take the characters of exogens as distinct from endogens; even under
ordinary circumstances, no absolute distinction can be drawn between
them. There are plants normally of an intermediate character, while, to
take exceptional instances, there are exogens with the leaves and
flowers of endogens, and endogens whose outward organisation, at any
rate, assimilates them to exogens. Diclinous or monochlamydeous plants
owe their imperfect conformation to suppression, and may become
structurally complete by a species of peloria. Structurally
hermaphrodite flowers become unisexual by suppression, or are rendered
incomplete by the non-development of one or more of their floral whorls.
Hypogynous flowers become perigynous by adhesion, or by lack of
separation; perigynous ones become hypogynous by an early detachment
from the receptacle that bears them, or by the arrested development of
an ordinarily cup-like receptacle.

How the relative position of the carpels and the calyx may be altered
has already been alluded to, as has also the circumstance that while it
is common to find an habitually inferior or adherent ovary becoming
superior or free, it is much more rare to find the superior ovary
adherent to the receptacle or to the calyx.[563] Regular and irregular
peloria, too, serve to show how slight are the boundaries, not only
between different genera, but also between different families.

While, therefore, teratology may be an unsafe guide in strictly
artificial schemes, it is obvious that its teachings should have great
weight in all philosophical systems of classification.

The questions will constantly arise, does such and such a form represent
the ancestral condition of certain plants? Is it a reversion to that
form