supposed becomes obvious from a
consideration of such facts as are mentioned under the head of Peloria,
while the presence of rudimentary organs, or the occasional appearance
of additional parts, or other changes, may, and often do, afford a clue
to the relationship existing between plants--a relationship that might
otherwise be unsuspected. So, too, some of the alterations met with
appear susceptible of no other explanations than that they are
reversions to some pre-existing form, or, at any rate, that they are
manifestations of a phase of the plant affected different from that
which is habitual, and due, as it were, to a sort of allotropism.

The mutations and perversions of form, associated as they commonly are
with corresponding changes of function, show the connection between
teratology and physiology--a connection which is seen to be the more
intimate when viewed in the light afforded by the writings and
experiments of Gaertner, Sprengel, and St. Hilaire, and, in our own
times, especially by the writings and experiments of Mr. Darwin, whose
works on the 'Origin of Species,' and particularly on the 'Variation of
Animals and Plants under Domestication' comprise so large a collection
of facts for the use of students in most departments of biology. It
will suffice to allude, in support of these statements, to the writings
of Mr. Darwin on such subjects as rudimentary organs, the use or disuse
of certain parts according to circumstances, the frequently observed
tendency of some flowers to become structurally unisexual, the liability
of other flowers perfectly organised to become functionally imperfect,
at least so far as any reciprocal action of the organs of the same
flower is concerned, reversions, classification, general morphology, and
other subjects handled at once with such comprehensive breadth and
minute accuracy of detail by our great physiologist.

In the following pages alterations of function, unless attended by
corresponding alterations of form, are either only incidentally alluded
to, or are wholly passed over; such, for instance, as alterations in the
period of flowering, in the duration of the several organs, and so
forth.[9] Pathological changes, lesions caused by insect puncture or
other causes, also find no place in this book, unless the changes are of
such a character as to admit of definite comparison with normal
conformation. Usually such changes are entirely heteromorphous, and, as
it were, fore