veloped;
on the other hand, in the spiral or successive arrangement there is no
such alternate growth and arrest of growth of the stem between the
leaves, or between successive cycles, but the growth is, under favorable
conditions, continuous--leaf is separated from leaf, and cycle from
cycle, by the continually elongating stem. Thus, the two modes of growth
correspond precisely with those observed in the case of definite and
indefinite inflorescence respectively.

[Illustration: FIG. 1.--Diagram showing the arrangement of parts in a
complete, regular, pentamerous flower: _s_, sepals; _p_, petals; _st_,
stamens; _o_, ovaries.]

The same arrangements, that are observed in the disposition of the
leaves, apply equally well to the several parts of the flower; thus, in
what is for convenience considered the typical flower, there is a calyx
of five or more distinct sepals, equal in size, and arranged in a whorl,
a corolla of a similar number of petals alternating with the sepals,
five stamens placed in the same position with reference to the petals,
and five carpels alternating with the stamens. Throughout this book this
arrangement is taken as the standard of reference. Nevertheless the
spiral order does occur in the floral leaves as well as in those of the
stem; it often happens, especially when the organs are numerous, that
they form spiral series; and the same holds good very generally, when
the parts of the flower are uneven in number, as in the very common
quincuncial arrangement of the sepals, &c.

To these general remarks, intended to show the agreement between the
disposition of the leaves of the stem and those of the flower, it is
merely necessary to add that the arrangement of the placentas, as well
as that of the ovules borne on them, is also definite, and takes place
according to methods explained in all the text-books, and on which,
therefore, it is not necessary to dilate in this place.

The branches of the stem or axis correspond for the most part in
disposition with that of the leaves from the axils of which they
originate, subject, however, to numerous disturbing causes, and to
alterations from the usual or typical order brought about by the
development of buds. These latter organs, as it seems, may be found in
almost any situation, though their ordinary position is in the axil of a
leaf or at the end of a stem or branch.

The points just mentioned are of primary importance in structural
botany, and as