Sec. 1. ANGIOSPERMOUS OR ORDINARY GYNOECIUM.
300. =Gynoecium= is the technical name for the pistil or pistils of a
flower taken collectively, or for whatever stands in place of these. The
various modifications of the gynoecium and the terms which relate to
them require particular attention.
301. The PISTIL, when only one, occupies the centre of the flower; when
there are two pistils, they stand facing each other in the centre of the
flower; when several, they commonly form a ring or circle; and when very
numerous, they are generally crowded in rows or spirals on the surface
of a more or less enlarged or elongated receptacle. Their number gives
rise to certain terms, the counterpart of those used for stamens (284),
which are survivals of the names of orders in the Linnaean artificial
system. The names were coined by prefixing Greek numerals to _-gynia_
used for gynoecium, and changed into adjectives in the form of
_-gynous_. That is, a flower is
_Monogynous_, when it has a single pistil, whether that be simple or
compound;
_Digynous_, when it has only two pistils; _Trigynous_, when with three;
_Tetragynous_, with four; _Pentagynous_, with five; _Hexagynous_, with
six; and so on to _Polygynous_, with many pistils.
302. =The Parts of a Complete Pistil=, as already twice explained (16,
236), are the OVARY, the STYLE, and the STIGMA. The ovary is one
essential part: it contains the rudiments of seeds, called OVULES. The
stigma at the summit is also essential: it receives the pollen, which
fertilizes the ovules in order that they may become seeds. But the
style, commonly a tapering or slender column borne on the summit of the
ovary, and bearing the stigma on its apex or its side, is no more
necessary to a pistil than the filament is to the stamen. Accordingly,
there is no style in many pistils: in these the stigma is _sessile_,
that is, rests directly on the ovary (as in Fig. 326). The stigma is
very various in shape and appearance, being sometimes a little knob (as
in the Cherry, Fig. 271), sometimes a point or small surface of bare
tissue (as in Fig. 327-330), and sometimes a longitudinal crest or line
(as in Fig. 324, 341-343), or it may occupy the whole length of the
style, as in Fig. 331.
303. The word Pistil (Latin, _Pistillum_) means a pestle. It came into
use in the first place for such flowers as those of Crown Imperial, or
Lily, in which the pistil in the centre was likened to the pestle, and
the perianth around it to the mortar, of the apothecary.
304. A pistil is either _simple_ or _compound_. It is simple when it
answers to a single flower-leaf, compound when it answers to two or
three, or a fuller circle of such leaves conjoined.
305. =Carpels.= It is convenient to have a name for each flower-leaf of
the gynoecium; so it is called a _Carpel_, in Latin _Carpellum_ or
_Carpidium_. A simple pistil is a carpel. Each component flower-leaf of
a compound pistil is likewise a carpel. When a flower has two or more
pistils, these of course are simple pistils, that is, separate carpels
or pistil-leaves. There may be only a single simple pistil to the
flower, as in a Pea or Cherry blossom (Fig. 271); there may be two such,
as in many Saxifrages; or many, as in the Strawberry. More commonly the
single pistil in the centre of a blossom is a compound one. Then there
is seldom much difficulty in ascertaining the number of carpels or
pistil-leaves that compose it.
306. =The Simple Pistil=, viewed morphologically, answers to a
leaf-blade with margins incurved and united where they meet, so forming
a closed case or pod (the ovary), and bearing ovules at the suture or
junction of these margins: a tapering upper portion with margins
similarly inrolled, is supposed to form the style; and these same
margins, exposed at the tip or for a portion of the length, become the
stigma. Compare, under this view, the three accompanying figures.
[Illustration: Fig. 323. An inrolled small leaf, such as in
double-flowered Cherry blossoms is often seen to occupy the place of a
pistil.]
[Illustration: Fig. 324. A simple pistil (of Isopyrum), with ovary cut
across; the inner (ventral) face turned toward the eye: the ovules seem
to be borne on the ventral suture, answering to leaf-margins: the stigma
above seen also to answer to leaf-margins.]
[Illustration: Fig. 325. Pod or simple pistil of Caltha or
Marsh-Marigold, which has opened, and shed its seeds.]
307. So a simple pistil should have a one-celled ovary, only one line of
attachment for the ovules, a single style, and a single stigma. Certain
variations from this normal condition which sometimes occur do not
invalidate this morphological conception. For instance, the stigma may
become two-lobed or two-ridged, because it consists of two leaf-margins,
as Fig. 324 shows; it may become 2-locellate by the turning or growing
inward of one of the sutures, so as to divide the cavity.
308. There are two or three terms which primarily relate to the parts of
a simple pistil or carpel, and are thence carried on to the compound
pistil, viz.:--
VENTRAL SUTURE, the line which answers to the united margins of the
carpel-leaf, therefore naturally called a suture or seam, and the
ventral or inner one, because in the circle of carpel-leaves it looks
inward or to the centre of the flower.
DORSAL 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 ovary 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 accordingly the pollen
can act upon the contained ovules only indirectly, through the stigma.
This is expressed in a term of Greek derivation, viz.:--
_Angiospermous_, meaning that the seeds are borne in a sac or closed
vessel. The counterpart term is
_Gymnospermous_, meaning naked-seeded. This kind of pistil, or
gynoecium, the simplest of all, yet the most peculiar, characterizes
the Pine family and its relatives.
[Illustration: Fig. 337. A pistil, that is, a scale of the cone, of a
Larch, at the time of flowering; inside view, showing its pair of naked
ovules.]
[Illustration: Fig. 338. Branchlet of the American Arbor-Vitae,
considerably larger than in nature, terminated by its pistillate
flowers, each consisting of a single scale (an open pistil), together
forming a small cone.]
[Illustration: Fig. 339. One of the scales or carpels of the last,
removed and more enlarged, the inside exposed to view, showing a pair of
ovules on its base.]
314. While the ordinary simple pistil is conceived by the botanist to be
a leaf rolled together into a closed pod (306), those of the Pine, Larch
(Fig. 337), Cedar, and Arbor-Vitae (Fig. 338, 339) are open leaves, in
the form of scales, each bearing two or more ovules on the inner face,
next the base. At the time of blossoming, these pistil-leaves of the
young cone diverge, and the pollen, so abundantly shed from the
staminate blossoms, falls directly upon the exposed ovules. Afterward
the scales close over each other until the seeds are ripe. Then they
separate that the seeds may be shed. As the pollen acts directly on the
ovules, such pistil (or organ acting as pistil) has no stigma.
315. In the Yew, and in Torreya and Gingko, the gynoecium is reduced
to extremest simplicity, that is, to a naked ovule, without any visible
carpel.
316. In Cycas the large naked ovules are borne on the margins or lobes
of an obvious open leaf. All GYMNOSPERMOUS plants have other
peculiarities, also distinguishing them, as a class, from ANGIOSPERMOUS
plants.