ary has as many DISSEPIMENTS, or internal _Partitions_, as
there are carpels in its composition. For these are the contiguous and
coalescent walls or sides of the component carpels. When such pistils
ripen into pods, they often separate along these lines into their
elementary carpels.

[Illustration: Fig. 331, 332. Pistil of a Sandwort, with vertical and
transverse section of the ovary: free central placenta.]

311. =One-celled, with free Central Placenta.= The commoner case is that
of Purslane (Fig. 272) and of the Pink and Chickweed families (Fig. 331,
332). This is explained by supposing that the partitions (such as those
of Fig. 329) have early vanished or have been suppressed. Indeed, traces
of them may often be detected in Pinks. On the other hand, it is equally
supposable that in the Primula family the free central is derived from
parietal placentation by the carpels bearing ovules only at base, and
forming a consolidated common placenta in the axis. Mitella and Dionaea
help out this conception.

[Illustration: Fig. 333. Plan of a one-celled ovary of three
carpel-leaves, with parietal placentae, cut across below, where it is
complete; the upper part showing the top of the three leaves it is
composed of, approaching, but not united.]

[Illustration: Fig. 334. Cross section of the ovary of Frost weed
(Helianthemum), with three parietal placentae, bearing ovules.]

[Illustration: Fig. 335. Cross section of an ovary of Hypericum
graveolens, the three large placentae meeting in the centre, so as to
form a three-celled ovary. 336. Same in fruit, the placentae now separate
and rounded.]

312. =One-celled, with Parietal Placentae.= In this not uncommon case it
is conceived that the two or three or more carpel-leaves of such a
compound pistil coalesce by their adjacent edges, just as sepal-leaves
do to form a gamosepalous calyx, or petals to form a gamopetalous
corolla, and as is shown in the diagram, Fig. 333, and in an actual
cross-section, Fig. 334. Here each carpel is an open leaf, or with some
introflexion, bearing ovules along its margins; and each placenta
consists of the contiguous margins of two pistil-leaves grown together.
There is every gradation between this and the three-celled ovary with
the placentae in the axis, even in the same genus, sometimes even in
different stages in the same pistil (Fig. 335, 336).

Sec. 2. GYMNOSPERMOUS GYNOECIUM.

313. The ordinary pistil has a closed ovary, and accord