_Hypogynous_, regular, ☿, gamopetalous flowers (Figs. 581, 582),
which are generally 5- or 4-merous, with 5 or 4 stamens (with the
exception of _Oleaceæ_ and _Jasminaceæ_ which have _only_ 2 stamens,
alternating with the carpels). The gynœceum is formed of 2 (nearly
always median) carpels. The corolla _very frequently has twisted
æstivation_ (the upper edges of the petals being free; Fig. 581 _A_),
and hence the individual lobes of the corolla are oblique, but the
flower as a whole is regularly actinomorphic. A nectary, in the form of
a honey-secreting ring or glands, is often found round the base of the
ovary.--The leaves, with a few exceptions, are _opposite_ and _without
stipules_. Endosperm large (Fig. 581 _C_), except in _Jasminaceæ_ and
_Asclepiadaceæ_.
The Apocynaceæ and the Asclepiadaceæ, on account of the free
ovaries, without doubt represent a more primitive form, but the
Asclepiadaceæ on the other hand form an offshoot on account of
their peculiar pollen-masses. The Loganiaceæ form a transition
to the Rubiaceæ.