=A.= PENTACYCLICÆ (FIVE-WHORLED). The flowers in this section have
5 _whorls equal in number_, namely, 2 staminal whorls in addition
to the calyx, corolla, and carpels; in some instances, one of the
staminal whorls is rudimentary or entirely suppressed, but in this
case it is frequently the sepal-stamens which are suppressed, and
the whorl which is present stands opposite the petals. The flowers
are regular. The _number of carpels equals that of the sepals_, but
in one of the orders (_Bicornes_) they are opposite the petals (the
flower being obdiplostemonous); in the other two orders (_Primulinæ_
and _Diospyrinæ_) they are placed opposite the sepals (the flower
being diplostemonous). This section is the most closely allied to the
Choripetalæ, since the petals may sometimes be found entirely free,
and the stamens inserted directly on the receptacle (Ericaceæ); ovules
with two integuments are also found. ~It is very doubtful, whether the
orders included under this head have any relationship with the other
Sympetalæ. They appear in any case to represent older types.~
=B.= TETRACYCLICÆ (FOUR-WHORLED). The flowers have only 4 whorls,
namely, beside sepals, petals, and carpels, only one whorl of stamens,
which alternates with the petals; there is no trace of the second
staminal whorl, and when the number of carpels is the same as that of
the preceding whorls (“isomerous”) they alternate with the stamens; but
in most cases there are 2 _carpels placed in the median plane_ (see the
diagrams, _e.g._ Figs. 559, 567, 583, 590, etc.). This section is the
largest, and the one which shows the characteristics of the Sympetalæ
best. Very irregular flowers are met with.
The following families belong to the =Pentacyclicæ=: 26, _Bicornes_;
27, _Diospyrinæ_; 28, _Primulinæ_.