Calyx.
The _sepals_ are sometimes _free_ or separate from each other, at other
times they are united to a greater or less extent; in the former case,
the calyx is _polysepalous_, in the latter _gamosepalous_ or
_monosepalous_. The divisions of the calyx present usually the
characters of leaves, and in some cases of monstrosity they are
converted into leaf-like organs, as not infrequently happens in
primulas. They are usually entire, but occasionally they are cut in
various ways, as in the rose; they are rarely stalked. Sepals are
generally of a more or less oval, elliptical or oblong form, with their
apices either blunt or acute. In their direction they are erect or
reflexed (with their apices downwards), spreading outwards (_divergent_
or _patulous_), or arched inwards (_connivent_). They are usually of a
greenish colour (_herbaceous_); but sometimes they are coloured or
_petaloid_, as in the fuchsia, tropaeolum, globe-flower and pomegranate.
Whatever be its colour, the external envelope of the flower is
considered as the calyx. The vascular bundles sometimes form a prominent
rib, which indicates the middle of the sepal; at other times they form
several ribs. The venation is useful as pointing out the number of
leaves which constitute a gamosepalous calyx. In a polysepalous calyx
the number of the parts is indicated by Greek numerals prefixed; thus, a
calyx which has three sepals is _trisepalous_; one with five sepals is
_pentasepalous_. The sepals occasionally are of different forms and
sizes. In Aconite one of them is shaped like a helmet (_galeate_). In a
gamosepalous calyx the sepals are united in various ways, sometimes very
slightly, and their number is marked by the divisions at the apex. These
divisions either are simple projections in the form of acute or obtuse
teeth (fig. 49); or they extend down the calyx as fissures about
half-way, the calyx being _trifid_ (three-cleft), _quinquefid_
(five-cleft), &c., according to their number; or they reach to near the
base in the form of partitions, the calyx being _tripartite_,
_quadripartite_, _quinquepartite_, &c. The union of the parts may be
complete, and the calyx may be quite entire or _truncate_, as in some
Correas, the venation being the chief indication of the different parts.
The cohesion is sometimes irregular, some parts uniting to a greater
extent than others; thus a two-lipped or _labiate_ calyx is formed. The
upper lip is often composed of three parts, which are thus posterior or
next the axis, while the lower has two, which are anterior. The part
formed by the union of the sepals is called the _tube_ of the calyx; the
portion where the sepals are free is the _limb_.
[Illustration: From Strasburger's _Lehrbuch der Botanik_, by permission
of Gustav Fischer.
FIG. 49.--Gamosepalous five-toothed calyx of Campion (_Lychnis_).
FIG. 50.--Obsolete calyx (c) of Madder (_Rubia_) adherent to the pistil,
in the form of a rim.
FIG. 51.--Feathery pappus attached to the fruit of Groundsel (_Senecio
vulgaris_).
FIG. 52.--Caducous calyx (c) of Poppy. There are two sepals which fall
off before the petals expand.
FIG. 53.--Fruit of Physalis Alkekengi, consisting of the persistent
calyx (s), surrounding the berry (fr), derived from the ovary. (After
Duchartre.)]
Occasionally, certain parts of the sepals undergo marked enlargement. In
the violet the calycine segments are prolonged downwards beyond their
insertions, and in the Indian cress (_Tropaeolum_) this prolongation is
in the form of a spur (_calcar_), formed by three sepals; in Delphinium
it is formed by one. In Pelargonium the spur from one of the sepals is
adherent to the flower-stalk. In _Potentilla_ and allied genera an
_epicalyx_ is formed by the development of stipules from the sepals,
which form an apparent outer calyx, the parts of which alternate with
the true sepals. In Malvaceae an epicalyx is formed by the bracteoles.
Degenerations take place in the calyx, so that it becomes dry, scaly and
glumaceous (like the glumes of grasses), as in the rushes (Juncaceae);
hairy, as in Compositae; or a mere rim, as in some Umbelliferae and
Acanthaceae, and in Madder (_Rubia tinctorum_, fig. 50), when it is
called _obsolete_ or _marginate_. In Compositae, Dipsacaceae and
Valerianaceae the calyx is attached to the pistil, and its limb is
developed in the form of hairs called _pappus_ (fig. 51). This pappus is
either simple (_pilose_) or feathery (_plumose_). In _Valeriana_ the
superior calyx is at first an obsolete rim, but as the fruit ripens it
is shown to consist of hairs rolled inwards, which expand so as to waft
the fruit. The calyx sometimes falls off before the flower expands, as
in poppies, and is _caducous_ (fig. 52); or along with the corolla, as
in _Ranunculus_, and is _deciduous_; or it remains after flowering
(_persistent_) as in Labiatae, Scrophulariaceae, and Boraginaceae; or
its base only is persistent, as in _Datura Stramonium_. In
_Eschscholtzia_ and _Eucalyptus_ the sepals remain united at the upper
part, and become disarticulated at the base or middle, so as to come off
in the form of a lid or funnel. Such a calyx is _operculate_ or
_calyptrate_. The existence or non-existence of an articulation
determines the deciduous or persistent nature of the calyx.
The receptacle bearing the calyx is sometimes united to the pistil, and
enlarges so as to form a part of the fruit, as in the apple, pear, &c.
In these fruits the withered calyx is seen at the apex. Sometimes a
persistent calyx increases much after flowering, and encloses the fruit
without being incorporated with it, becoming _accrescent_, as in various
species of _Physalis_ (fig. 53); at other times it remains in a withered
or _marcescent_ form, as in _Erica_; sometimes it becomes _inflated_ or
_vesicular_, as in sea campion (_Silene maritima_).
Corolla.
The corolla is the more or less coloured attractive inner floral
envelope; generally the most conspicuous whorl. It is present in the
greater number of Dicotyledons. Petals differ more from ordinary leaves
than sepals do, and are much more nearly allied to the staminal whorl.
In some cases, however, they are transformed into leaves, like the
calyx, and occasionally leaf-buds are developed in their axil They are
seldom green, although occasionally that colour is met with, as in some
species of _Cobaea_, _Hoya viridiflora_, _Gonolobus viridiflorus_ and
_Pentatropis spiralis_. As a rule they are highly coloured, the
colouring matter being contained in the cell-sap, as in blue or red
flowers, or in plastids (chromoplasts), as generally in yellow flowers,
or in both forms, as in many orange-coloured or reddish flowers. The
attractiveness of the petal is often due wholly or in part to surface
markings; thus the cuticle of the petal of a pelargonium, when viewed
with a 1/2 or 1/4-in. object-glass, shows beautiful hexagons, the
boundaries of which are ornamented with several inflected loops in the
sides of the cells.
Petals are generally glabrous or smooth; but, in some instances, hairs
are produced on their surface. Petaline hairs, though sparse and
scattered, present occasionally the same arrangement as those which
occur on the leaves; thus, in Bombaceae they are stellate. Coloured
hairs are seen on the petals of _Menyanthes_, and on the segments of the
perianth of _Iris_. They serve various purposes in the economy of the
flower, often closing the way to the honey-secreting part of the flower
to small insects, whose visits would be useless for purposes of
pollination. Although petals are usually very thin and delicate in their
texture, they occasionally become thick and fleshy, as in _Stapelia_ and
_Rafflesia_; or dry, as in heaths; or hard and stiff, as in _Xylopia_. A
petal often consists of two portions--the lower narrow, resembling the
petiole of a leaf, and called the _unguis_ or _claw_; the upper broader,
like the blade of a leaf, and called the _lamina_ or _limb_. These parts
are seen in the petals of the wallflower (fig. 54). The claw is often
wanting, as in the crowfoot (fig. 55) and the poppy, and the petals are
then _sessile_. According to the development of veins and the growth of
cellular tissue, petals present varieties similar to those of leaves.
Thus the margin is either entire or divided into lobes or teeth. These
teeth sometimes form a regular fringe round the margin, and the petal
becomes _fimbriated_, as in the pink; or _laciniated_, as in _Lychnis
Flos-cuculi_; or _crested_, as in _Polygala_. Sometimes the petal
becomes pinnatifid, as in _Schizopetalum_. The median vein is
occasionally prolonged beyond the summit of the petals in the form of a
long process, as in _Strophanthus hispidus_, where it extends for 7 in.;
or the prolonged extremity is folded downwards or inflexed, as in
Umbelliferae, so that the apex approaches the base. The limb of the
petal may be flat or concave, or hollowed like a boat. In Hellebore the
petals become folded in a tubular form, resembling a horn (fig. 56); in
aconite (fig. 58) some of the petals resemble a hollow-curved horn,
supported on a grooved stalk; while in columbine, violet (fig. 57),
snapdragon and _Centranthus_, one or all of them are prolonged in the
form of a spur, and are _calcarate_. In _Valeriana_, _Antirrhinum_ and
_Corydalis_, the spur is very short, and the corolla or petal is said to
be _gibbous_, or _saccate_, at the base. These spurs, tubes and sacs
serve as receptacles for the secretion or containing of nectar.
[Illustration:
FIG. 54.--Unguiculate or clawed petal of Wallflower (_Cheiranthus
Cheiri_). c, The claw or unguis; l, the blade or lamina.
FIG. 55.--Petal of Crowfoot (_Ranunculus_), without a claw, and thus
resembling a sessile leaf. At the base of the petal a nectariferous
scale is seen.
FIG. 56.--Tubular petal of Hellebore (_Helleborus_).
FIG. 57.--Pansy (_Viola tricolor_). Longitudinal section of flower; v,
bracteole on the peduncle; l, sepals; ls, appendage of sepal; c, petals;
cs, spur of the lower petals; fs, glandular appendage of the lower
stamens; a, anthers. (After Sachs.)
(From Vines' Students' _Text-Book of Botany_, by permission of Swan
Sonnenschein & Co.)
FIG. 58.--Part of the flower of Aconite (_Aconitum Napellus_), showing
two irregular horn-like petals (p) supported on grooved stalks (o).
These serve as nectaries, s, the whorl of stamens inserted on the
thalamus and surrounding the pistil.]
A corolla is _dipetalous_, _tripetalous_, _tetrapetalous_ or
_pentapetalous_ according as it has two, three, four or five separate
petals. The general name of _polypetalous_ is given to corollas having
separate petals, while _monopetalous_, _gamopetalous_ or _sympetalous_
is applied to those in which the petals are united. This union generally
takes place at the base, and extends more or less towards the apex; in
_Phyteuma_ the petals are united at their apices also. In some
polypetalous corollas, as that of the vine, the petals are separate at
the base and adhere by the apices. When the petals are equal as regards
their development and size, the corolla is _regular_; when unequal, it
is _irregular_. When a corolla is gamopetalous it usually happens that
the lower portion forms a tube, while the upper parts are either free or
partially united, so as to form a common limb, the point of union of the
two portions being the _throat_, which often exhibits a distinct
constriction or dilatation. The number of parts forming such a corolla
can be determined by the divisions, whether existing as teeth,
crenations, fissures or partitions, or if, as rarely happens, the
corolla is entire, by the venation. The union may be equal among the
parts, or some may unite more than others.
[Illustration: FIG. 59.--Rosaceous corolla (c) of the Strawberry
(_Fragaria vesca_), composed of five petals without claws.]
Amongst regular polypetalous corollas may be noticed the _rosaceous_
corolla (fig. 59), in which there are five spreading petals, having no
claws, and arranged as in the rose, strawberry and _Potentilla_; the
_caryophyllaceous_ corolla, in which there are five petals with long,
narrow, tapering claws, as in many of the pink tribe; the _cruciform_,
having four petals, often unguiculate, placed opposite in the form of a
cross, as seen in wallflower, and in other plants called _cruciferous_.
Of irregular polypetalous corollas the most marked is the
_papilionaceous_ (fig. 40), in which there are five petals:--one
superior (posterior), st, placed next to the axis, usually larger than
the rest, called the _vexillum_ or _standard_; two lateral, a, the
_alae_ or wings; two inferior (anterior), partially or completely
covered by the alae, and often united slightly by their lower margins,
so as to form a single keel-like piece, _car_, called _carina_, or keel,
which embraces the essential organs. This form of corolla is
characteristic of British leguminous plants.
[Illustration: From Strasburger's _Lehrbuch der Botanik_, by permission
of Gustav Fischer.