The flowers in this family are perfect, regular (except _Resedaceæ,
Violaceæ_), hypogynous, the perianth-leaves free (a few have them
slightly united), æstivation most frequently imbricate; they are
eucyclic in the andrœcium, and most frequently in the other parts,
and generally 5-merous with S5, P5, A5 + 5, G3, but other numbers
also occur; several have _indefinite stamens_, but the stamens arise
(where the development is known) in _centrifugal order_ and are
arranged, often very distinctly, _in bundles_; in other words, the
large number of stamens is formed by the splitting of a small number
(most frequently 5); a true spiral arrangement is never found. Gynœceum
syncarpous, multicarpellary (_Dilleniaceæ_ and a few _Resedaceæ_ are
apocarpous), most frequently the number of carpels is 3, forming a
_unilocular ovary_ with _parietal placentæ_, but parallel with this,
multilocular ovaries, with the ovules placed in the inner angle of the
loculi, are also found, and a few genera have a free, centrally-placed
placenta. The fruit is most frequently a capsule. The dehiscence is
never with a “replum,” _i.e._ the persistent frame of the placenta,
as in the family Rhœadinæ. One half of the orders has endosperm
(_Violaceæ_, _Cistaceæ_, _Droseraceæ_, _Bixaceæ_, _Ternstrœmiaceæ_,
etc.), the other has no endosperm (_Resedaceæ_, _Hypericaceæ_,
_Elatinaceæ_, _Tamaricaceæ_, etc.); some have a curved, the majority a
straight embryo. ~The family is scarcely quite natural; in the future
the orders will probably be arranged differently.~
Order 1. =Resedaceæ (Mignonettes).=--Herbs or small shrubs with
spirally-placed leaves and very small, gland-like stipules (as in
Cruciferæ); the ☿, hypogynous flowers are _zygomorphic_, and arranged
in racemes or spikes typically without bracteoles. The zygomorphic
structure is produced by the _greater development of the posterior side
of the flower_, especially the petals and the nectary (“disc,” in Fig.
416 _d_) which is situated between the petals and stamens; in general
there are 5–8 free sepals and petals, the latter consisting of a large
scale-like _sheath_ with a fimbriated blade (see Fig. 416); stamens
numerous; carpels 6–2 united together; ovary unilocular with parietal
placentæ, but _the cavity of the ovary is not closed_ at the top. In
_Astrocarpus_ the gynœceum is apocarpous. The fruit is most frequently
a capsule; the seeds are reniform, without endosperm, and the embryo is
_curved_.
This order connects the Rhœadinæ with the Cistifloræ. It is
closely allied to the Rhœadinæ by its external appearance, even
by the smell and taste, the parietal placentation, structure of
the seeds, the inflorescences, etc., whilst by the irregular
flowers and the disc placed at the posterior side of the
flower, _it is allied to Capparidaceæ_, but differs from this
order in not having its characteristic number (2–4) and by
the very different mode of dehiscence of the fruit, etc. It
differs from the other orders of this family chiefly in the
fact that the number of the perianth-leaves is not constantly
5. In _Reseda luteola_ both the calyx and corolla appear to
be 4-leaved, because the posterior sepal is suppressed, and
the 2 posterior petals are united. Where there are 10 stamens,
they stand in 2 whorls, _i.e._ in front of the sepals and
petals; if there are several, their position depends upon the
splitting.--_Astrocarpus_ is remarkable for its apocarpous fruit
and the position of the ovules on the _dorsal_ suture of the
carpel.
The yellow, flat disc at the back of the flower serves as a
nectary, the honey being protected by the lobes of the petals.
If pollination by insects is not effected, then self-pollination
may take place, at all events in _R. odorata_.
45 species; the majority in the Mediterranean and in Persia.
_Reseda odorata_ (from Egypt) is cultivated on account of its
sweet scent; _R. luteola_ (“Dyer’s Weed”) yields a yellow dye.
[Illustration: FIG. 416.--Diagram of _Reseda odorata_.]
Order 2. =Droseraceæ (Sundews).= Herbs, chiefly living on moors or in
water, and whose leaves are adapted to catch and digest small animals.
With regard to the flower, they are closely allied to the Violaceæ,
especially to those with regular flowers. _Drosera_ (Sundew) has a
long-stalked scorpioid cyme with regular, ☿, hypogynous flowers,
5-merous as in _Viola_. S5, P5, A5, G3 (in a syncarpous gynœceum,
with free, bifid styles and basal or parietally-placed ovules in the
unilocular ovaries). The capsule opens also as in _Viola_, but, among
other differences, the styles are free, the seeds very small, and
surrounded by a loosely lying, thin shell. ~_Drosera_ has radical,
long-stalked leaves with the blade (Fig. 417) covered by numerous
strong glandular hairs, placed on the edge and in the middle; when
small animals are caught by these hairs, the latter and the entire
blade close slowly over them dissolving and absorbing all the
digestible matter as nourishment.~
[Illustration: FIG. 417.--Leaf-rosette of _Drosera rotundifolia_
(nat. size), and a leaf (magnified).]
_Dionæa muscipula_ (Fly-trap; N. Am.) has the same appearance
as _Drosera_, but the leaves are constructed as in Fig. 418.
The stalk is flat and winged, the blade small, circular, with
powerful, pointed teeth along the edge, and on its surface are 6
small bristles (_A_), which are very sensitive. When these are
touched the blade quickly closes, folding along the midrib (_B_,
_C_) and imprisoning the irritating object, the teeth round the
edges fitting like the teeth of a trap. If it happens to be an
insect or similar body, a digestive fluid is secreted which,
like the gastric juice, dissolves the digestible portions.
_Aldrovandia vesiculosa_ (Central and S. Europe) captures small
aquatic animals in a similar manner; it is a floating, aquatic
plant, the two halves of its leaves also close together when
irritated (Fig. 419).--_Drosophyllum._
About 110 species; most of them in the temperate regions.
[Illustration: FIG. 418.--_Dionæa muscipula._ Leaves (nat. size).]
Orders 3 and 4. =Sarraceniaceæ and Nepenthaceæ.= These two
orders are perhaps most closely allied to the Droseraceæ and
agree with these, among other things, in the manner of taking
nourishment. Like the Droseraceæ they absorb nitrogenous food
from dissolved animal matter by means of their leaves, which are
specially constructed both to catch, to retain, and to digest
any small animals which may be caught. The SARRACENIACEÆ are
North American marsh-plants (10 species) which have pitcher-like
leaf-stalks, in the cavity of which a fluid (with properties
approaching those of gastric juice) is secreted, and which bear
at the apex a small, lid-like blade; these leaf-stalks are the
catching and digestive organs.--_Sarracenia, Darlingtonia._
[Illustration: FIG. 419.--_Aldrovandia vesiculosa_: _A_ a plant
(nat. size). _B_ Leaf (mag.); the blade is closed; the winged
stalk is prolonged into 4–6 irritable bristles.]
[Illustration: FIG. 420.--_Nepenthes_ (reduced).]
NEPENTHACEÆ has only 1 genus, _Nepenthes_ (the Pitcher-plant;
about 35 species), especially found in tropical E. Asia; the
majority are climbing shrubs. The leaf-stalks are twining
organs, and terminate either simply in a tendril, or in addition
to this, with a pitcher-shaped body (which in some species may
be as much as a foot in length) on whose upper edge a lid-like
structure is found (Fig. 420). In this pitcher, as among the
Sarraceniaceæ, a fluid is secreted which is able to digest the
animals captured (sometimes rather large) and which corresponds
in some degree to the gastric juice.
Order 5. =Violaceæ (Violets).= The flowers are ☿, and generally
zygomorphic, hypogynous, with S5, P5, A5, G3 (Fig. 421). The stamens
are closely applied to the ovary, they have a very short filament,
and at their summit generally a membranous appendage formed by the
prolongation of the connective (Fig. 422 _g_). The ovary is unilocular
with 3 parietal placentæ; style undivided (Fig. 422 _B_). The fruit
is usually a 3-valved capsule, opening along the dorsal sutures
(Fig. 423). Embryo straight; endosperm fleshy (Fig. 425).--Many are
herbaceous plants (_e.g. Viola_), but in the Tropics shrubs are also
found (_e.g. Ionidium_); a few are lianes; the leaves are scattered,
with stipules, and involute in the bud.
[Illustration: FIG. 421.--Diagram of _Viola_.]
[Illustration: FIG. 422.--The large-flowered form of _Viola
tricolor_: _A_ the flower in median longitudinal section; _B_ the
gynœceum.]
_Viola._ The sepals are prolonged backwards beyond the point of
insertion (appendiculate); the corolla is polypetalous, descending
imbricate, and zygomorphic, its anterior petal being larger than the
others and provided with a spur (Fig. 421). The 2 anterior of the 5
almost sessile stamens are provided with a spur-like nectary, which
protrudes a considerable distance into the petaloid spur (Figs. 421,
422 _n_, _sp_). The style is club-like, and bears the stigma in a
groove on the anterior side (Fig. 422 _st_). ~Herbs with rhizomes,
or annuals; flowers solitary. _V. odorata_, _canina_, etc., have
cleistogamic flowers which produce fruit in addition to the large,
coloured (violet) flowers. The Pansy (_V. tricolor_) has large flowers
adapted for insect-pollination, and also smaller, less conspicuous
ones designed for self-pollination. The stigma, as in Fig. 422 _A_,
_st_, and _B_, is situated on the anterior side of the stylar-head,
immediately in front of the channel leading down to the spur (_sp_);
below it is situated a valve, easily covered with pollen when
the proboscis of an insect is introduced into the spur, but which
closes upon its withdrawal; cross-pollination is thus secured.--The
sweet-scented _V. odorata_ is visited by the honey-bee, which insures
cross-pollination, and in the absence of insect visits it effects
self-fertilisation by cleistogamic flowers. The conspicuous but
scentless _V. tricolor_, var. _vulgaris_, is less frequently visited by
insects (humble-bees). In _V. silvatica_ and _V. canina_ the pollen is
carried on the head or proboscis of the honey-sucking bee.--The fruits
of _V. odorata_ bury themselves slightly in the soil. In the others
the fruits are raised above the ground; the 3 boat-shaped valves close
together along the central line, and eject the seeds, one by one, with
much violence, so that they are thrown to a great distance.~
[Illustration: FIGS. 423–425.--_Viola Tricolor._
FIG. 423.--Capsule after dehiscence (nat. size).
FIG. 424.--External view of the seed.