The flowers are hypogynous, ☿, polypetalous, usually regular (except
_Pelargonium_, _Tropæolaceæ_, _Balsaminaceæ_) and _throughout
5-merous_: S5, P5, A5 + 5, or 5 + 0, G5 (_epipetalous_). The stamens
soon fall off and are _obdiplostemonous_, often united at the base
(_monadelphous_); the corolla-stamens are in some completely suppressed
(_e.g. Balsaminaceæ_, Fig. 438), in others reduced to teeth (_Linum_,
Fig. 431; _Erodium_). The _Tropæolaceæ_ have 3 carpels and only 8
stamens (Fig. 437). Ring-like nectaries are not present, but at most
only glandular bodies, borne outside the base of the stamens. Ovaries
many-locular. The ovules as a rule are pendulous, with the micropyle
directed outwards (Fig. 431, B), and the radicle therefore also points
outwards. Usually _herbs_. Related to the Columniferæ.
Order 1. =Oxalidaceæ.= Most of the species are herbs with rhizomes;
the leaves are stalked, _compound_, with entire leaflets which are
folded and bent backwards in the bud (and in the sleep position),
exstipulate; some species have sensitive leaves. The flowers (Fig. 429)
are regular, and have S5, P5, which are _twisted_ to the left or right
in æstivation, A5 + 5, all united at the base (monadelphous), gynœceum
5-carpellate, _styles 5 free_, stigmas capitate, ovary 5-locular,
ovules numerous. The fruit is a _capsule opening_ with clefts _on the
dorsal sutures_ through which the seeds are ejected, while the _fleshy,
external layer of the testa_ springs off elastically. Embryo straight.
Endosperm.
[Illustration: FIG. 429.--Diagram of _Oxal’s acetosella_.]
_Oxalis_ (Wood-Sorrel). Leaves digitate. Species also occur
with phyllodia, _i.e._ leaf-like petioles placed vertically
without lamina; a few have pinnate leaves. The flowers are
situated singly or in dichasia, and unipared scorpioid cymes.
The pollination is effected by insects. Some species are
trimorphic (long-, short-, medium-styled flowers) and some,
_e.g. O. acetosella_, have cleistogamic flowers in addition
to the ordinary ones. Glands are found on the outer side of
the corolla-stamens or of all the stamens. _O. tetraphylla_
and others have adventitious edible roots, resembling
tap-roots.--_Averrhoa_ is a tropical tree, with berries and
pinnate leaves.
235 species (205 belong to _Oxalis_); chiefly in S. Africa and
Trop. America.--Oxalate of potash is contained in the leaves of
_Oxalis_.
Order 2. =Linaceæ.= Herbs with scattered or opposite, sessile,
_simple_, small, entire leaves, without (rarely with small) stipules.
The flowers (Fig. 430) are regular, 5- or 4-merous. Petals are free,
_twisted_, quickly falling off. Stamens united at the base; the
petal-stamens _are either reduced to teeth_ (Fig. 431 _A_, _m_) _or
entirely suppressed_. _Styles free._ The (5–4) epipetalous loculi
of the ovary are incompletely halved by _false divisional walls_,
each half contains one ovule (Fig. 431 _C_). The fruit is a spherical
_capsule, dehiscing along the divisional wall_ (Fig. 432); the 10 (-8)
seeds have a straight embryo and very slight endosperm (Fig. 433).
[Illustration: FIGS. 430–433.--_Linum usitatissimum._
Fig. 430.--The Flax plant.
Fig. 431.--_A_ Flower after removal of sepals and petals; _m_
petal-stamens reduced to teeth. _B_ Longitudinal section of
ovary. _C_ Transverse section of capsule.
Fig. 432.--Capsule (nat. size).
Fig. 433.--Transverse and longitudinal section of seed: _bl_ the
cotyledons; _k_ the plumule; _R_ the radicle; _fr_ the endosperm;
_sk_ the testa.]
_Linum_ (Flax) has 5-merous flowers. ~The main axis terminates in a
flower; and the succeeding branching is cymose, or unipared scorpioid
branching by unilateral development, and the flowers in consequence of
the vigorous sympodial development of the lateral axis (and also by the
leaves being displaced and pushed aside), assume a position apparently
lateral (_i.e._ racemose) without bracts; each branch of the sympodium
generally has 2 leaves. The testa is shining and smooth when dry, but
its external cellular layer becomes mucilaginous in water.~--_Radiola_
has a 4-merous flower. It is a small herb with opposite leaves, and
regular, dichasial branching.
The anthers and stigmas in _L. catharticum_ and _usitatissimum_
develop simultaneously, and cross-pollination as well as
self-pollination takes place. _L. grandiflorum_, _perenne_,
and others, are dimorphic (short-and long-styled). There are 5
nectaries outside the stamens.
130 species; _Linum_ and _Radiola_ are native genera.--_L.
usitatissimum_ is extensively cultivated in Europe (especially
in Russia and Belgium), N. America and elsewhere (its home no
doubt being Asia), partly on account of the oil (linseed oil)
which is extracted from the seeds, and partly on account of
the bast of the stem, which has very thick-walled cells. The
seeds and oil are OFFICINAL. The species cultivated in ancient
times was _L. angustifolium_. Several species are cultivated as
ornamental plants.
Order 3. =Geraniaceæ.= The majority are herbs with dichasial branching,
and scattered or opposite, stalked, _palminerved_ (rarely penninerved)
leaves with small _stipules_. The flowers are regular (except
_Pelargonium_) and 5-merous, with 10 or 5 stamens, which are slightly
united at the base. Nectaries alternate with the corolla-stamens.
The ovary is most frequently 5-locular, deeply 5-grooved, and bears
1 _well developed style_ (“beak”), which towards the apex divides
into 5 branches bearing stigmas; ovules 1 in each loculus, pendulous
or ascending. _The 5 carpels become detached from one another when
ripe_, and bend or _roll back_ (Fig. 434) or become _spirally twisted_
in the upper “beak-like” part (Figs. 435, 436), whilst a _central
column_ (septal column) persists; each carpel, in consequence, remains
either closed, and the fruit is a 5-merous _schizocarp_ whose nut-like
lower portion, containing the seed, is forced into the ground, thus
burying the seed by the movements of the spirally-twisted, hygroscopic
“beak” (Figs. 435, 436); or it opens along the ventral suture, so
that the seeds may fall out, and it is then a 5-valved _capsule_,
with septicidal dehiscence (Fig. 434) and the rolling up often takes
place so suddenly and violently that the seeds are shot out to
considerable distances. The embryo is usually green and _curved_, and
the _cotyledons are folded_; endosperm is wanting.
_Geranium_ (Crane’s-bill) has 5 + 5 stamens,and a septicidal capsule;
the carpels most frequently remain suspended from the apex of the
column (Fig. 434). The leaves are most frequently palminerved. The
flowers are situated solitarily or 2 together (2-flowered scorpioid
cyme).--_Erodium_ (Stork’s-bill); inflorescence a many-flowered
unipared scorpioid cyme, stamens 5 + 0 (petal-stamens are wanting), and
fruit a schizocarp whose carpels become detached; their beaks are hairy
on the internal surface and _twist themselves spirally_ (Fig. 436).
The umbellate inflorescences are composed of multiflowered scorpioid
cymes. The leaves are often penninerved.--~The most primitive type is
represented by _Biebersteinia_: S5, P5, A5 + 5, G5 (ovaries _free_,
and styles united above); fruit 5 small nuts. The most advanced type
is _Pelargonium_, which has _zygomorphic_ flowers, the posterior sepal
being prolonged into a spur which becomes adnate to the peduncle;
the petals are unequal in size; some of the petal-stamens are often
wanting. (_Erodium_ may be slightly zygomorphic).~
[Illustration: FIG. 434.--_Geranium sanguineum._ Fruit (3/1).]
[Illustration: FIG. 435.--_Pelargonium._]
[Illustration: FIG. 436.--_Erodium cicutarium_, detached carpel.]
POLLINATION. The large-flowered _Geranium_-species are
protandrous, _e.g. G. pratense_ (one whorl of stamens opens
first, and then the other, and succeeding these the stigmas,
after shedding the pollen the stamens bend outwards); the
small-flowered are also adapted, with various modifications,
for self-pollination.--470 species; moderately hot climates,
especially S. Africa.--Several _Pelargonium_-species, with
numerous varieties, are ornamental plants (from S. Africa).
Order 4. =Tropæolaceæ.= Herbaceous, juicy plants which have scattered,
long-stalked, peltate leaves without stipules, and often climb by their
sensitive petioles. The flowers are situated singly in the axils of the
foliage-leaves on long stalks, and are _zygomorphic_, the receptacle
under the posterior sepal being prolonged _into a spur_; there are also
differences between the posterior and anterior petals, the 2 posterior
petals situated on the border of the spur being _perigynous_, and the
edge of the anterior petals adjoining the claw fringed. After the 5
sepals (which are more or less coloured) and the 5 petals, follow 8
_stamens_ (as the 2 median ones are suppressed, one from each whorl)
and a gynœceum formed of 3 carpels; in each of the 3 loculi of the
3-grooved ovary is 1 ovule. The fruit is a _schizocarp_ and divides
into 3 1-seeded, _drupe-like_ fruitlets, which do not (as in the
Geraniaceæ) leave any pronounced column between them. Endosperm is
wanting. The cotyledons are thick and sometimes slightly coalescent.
~Tubers often occur.~
[Illustration: FIG. 437.--Diagram of _Tropæolum_: _sp_, spur.]
_Tropæolum._--About 40 species; all from America.
POLLINATION.--The spur is the receptacle for the nectar; the
flowers are protandrous; the anthers open first, and one by
one take up a position in front of the entrance to the spur,
resuming their original position when the pollen is shed; the
stigma finally takes their place after the filaments have bent
backwards.--These plants have an acrid taste (hence the name
“Nasturtium,” “Indian Cress”), on which account the flower-buds
and young fruits of _T. majus_ are used as capers. Some species
are ornamental plants.
Order 5. =Balsaminaceæ.= Herbaceous, chiefly annual plants with
juicy, brittle stems, so transparent that the vascular bundles may be
distinctly seen. The leaves are simple, usually scattered, penninerved
and dentate; stipules are wanting, but sometimes large glands are
present in their place at the base of the petioles. The flowers are
strongly zygomorphic; of their five 5-merous whorls the petal-stamens
are suppressed (S5, P5, A5 + 0, G5); the sepals are _coloured_, the
2 _anterior ones_ (Fig. 438 _3_, _5_) _are very small_ or entirely
suppressed, _the posterior one_ is very large and _elongated into a
spur_, and the 2 lateral ones pushed forward; sometimes the weight
of the spur turns the flower completely round, so that the posterior
leaves assume an anterior position; apparently only 3 petals, since
the lateral and the posterior petals become united in pairs, and
the anterior is larger and differently shaped; the 5 stamens have
very short and thick filaments united at the base, and their anthers
finally adhere together and remain in this condition, covering over
the gynœceum; the filaments ultimately rupture at the base, and the
entire anthers are raised on the apex of the gynœceum as it grows
up. The gynœceum has a _sessile stigma_ and a 5-locular ovary. The
fruit is a capsule which, on maturity, opens suddenly when irritated,
dividing into valves from the base upwards, and as the 5 valves roll
up elastically, the seeds are shot out on all sides to considerable
distances; a central column persists (Fig. 439). The embryo is
straight, and without endosperm.
[Illustration: FIG. 438.--Diagram of _Impatiens glanduligera_.]
[Illustration: FIG. 439.--Fruit of _Impatiens_.]
_Impatiens_; in Europe only _I. noli-me-tangere_. 225 species;
especially from Asia. Several species have two kinds of flowers:
small, cleistogamic, but fertile; and large, coloured flowers,
which in _I. balsamine_ (ornamental plant, E. Ind.) are
protandrous and pollinated by hive-and humble-bees, as they suck
the honey from the spur.
Order 6. =Limnanthaceæ.= The flowers are regular and differ
from all the other orders in the family by having the carpels
not in front of the petals, but _in front of the sepals_
(which are _valvate_), and further, the loculi are nearly
_free individually_, but with a _common gynobasic_ style;
the ovules are _ascending_ and _apotropous_ (anatropous with
ventral raphe). The fruit is a schizocarp, with nut-like
cocci.--_Limnanthes_ (4 species; N. Am.) perhaps belongs to
another family.
Order 7. =Humiriaceæ.= Trees and shrubs; about 20 species; Trop.
Am.