SAL SUTURE is the line down the back of the carpel, answering to the
midrib of the leaf,--not a seam therefore; but at maturity many fruits,
such as pea-pods, open by this dorsal as well as by the ventral line.

PLACENTA, a name given to the surface, whatever it be, which bears the
ovules and seeds. The name may be needless when the ovules grow directly
on the ventral suture, or from its top or bottom; but when there are
many ovules there is usually some expansion of an ovule-bearing or
seed-bearing surface; as is seen in our Mandrake or Podophyllum, Fig.
326.

[Illustration: Fig. 326. Simple pistil of Podophyllum, cut across,
showing ovules borne on placenta.]

[Illustration: Fig. 327. Pistil of a Saxifrage, of two simple carpels or
pistil-leaves, united at the base only, cut across both above and
below.]

[Illustration: Fig. 328. Compound 3-carpellary pistil of common St.
John's-wort, cut across: the three styles separate.]

[Illustration: Fig. 329. The same of shrubby St. John's-wort; the three
styles as well as ovaries here united into one.]

[Illustration: Fig. 330. Compound 3-carpellary pistil of Tradescantia or
Spiderwort; the three stigmas as well as styles and ovary completely
coalescent into one.]

309. =A Compound Pistil= is a combination of two, three, or a greater
number of pistil-leaves or carpels in a circle, united into one body, at
least by their ovaries. The annexed figures should make it clear. A
series of Saxifrages might be selected the gynoecium of which would
show every gradation between two simple pistils, or separate carpels,
and their complete coalescence into one compound and two-celled ovary.
Even when the constituent styles and stigmas are completely coalescent
into one, the nature of the combination is usually revealed by some
external lines or grooves, or (as in Fig. 328-330) by the internal
partitions, or the number of the placentae. The simplest case of compound
pistil is that

310. =With two or more Cells and Axile Placentae=, namely, with as many
cells as there are carpels, that have united to compose the organ. Such
a pistil is just what would be formed if the simple pistils (two, three,
or five in a circle, as the case may be), like those of a Paeony or
Stonecrop (Fig. 224, 225), pressed together in the centre of the flower,
were to cohere by their contiguous parts. In such a case the placentae
are naturally _axile_, or all brought together in the axis or centre;
and the ov