growth or development. The researches of organogenists have, however,
dispelled this idea of unvarying primordial regularity, by showing that
in many cases flowers are irregular from the very first, that some begin
by being irregular, and subsequently become regular, and even in some
cases resume their original condition during the course of their
development.[218] Under these circumstances an artificial standard of
comparison becomes almost an absolute necessity for the time being.

Changes of form very generally, but not always, are accompanied with a
change in regularity: thus a flower habitually bi-lateral may assume the
characters of radiating symmetry and _vice versa_. Increase or decrease
of size very frequently also are co-existent with an alteration in the
usual form.

In the case of the arrangement of organs it is often difficult or
impossible, in the present state of our knowledge, to determine whether
a given arrangement is congenital or acquired subsequently to the first
development, whether for instance an isolation of parts be due to
primordial separation or to a subsequent disunion of originally combined
organs, see p. 58. With reference to the changes in the form of organs,
however, it is in general more easy to ascertain the proximate cause of
the appearance, and thus teratological changes of form may be grouped
according as they are due to, 1, arrest of development; 2, undue or
excessive development; 3, perverted development; and 4, irregular
development; hence the use of the following terms--Stasimorphy,
Pleiomorphy, Metamorphy, and Heteromorphy--to include teratological
changes really or apparently due to one or other of the causes above
mentioned. The classification here adopted is of course to a
considerable extent an arbitrary one and subject to correction or
modification, as the knowledge of the development of the flowers in the
various genera of plants advances.

FOOTNOTES:

[217] The word symmetry has been used in very different senses by
different botanists, sometimes as synonymous with "regularity," at other
times to express the assumed typical form of a flower. Payer understands
it to be that arrangement of parts which permits of the whole flower
being divided vertically into two symmetrical halves (bi-lateral
symmetry). Others, again, have applied the term symmetry to the number
of the parts of the flower, reserving the terms "regularity" or
"irregularity" for the form. It is here us