_Cassia_ (Figs. 508–510) is the largest genus (about 200 species); it
has an almost hypogynous, zygomorphic flower with 5 free sepals and
petals; of the 10 stamens the 3 posterior are generally barren, the
others are of very unequal length and open at the apex by _pores_ (Fig.
509). In some (the _Senna_ group) the fruit is a flat, short, thin,
dehiscing pod; in others (_Cathartocarpus_) it is round, long, woody
or fleshy, indehiscent, and divided internally by more or less fleshy
transverse walls into as many cells as there are seeds.--The following
also have DEHISCENT FRUITS: _Bauhinia_ (often lianes, tropical climbers
with tendrils [stem-structures] and anomalous stems), _Copaifera_,
_Hæmatoxylon_ (whose pod does not dehisce along the suture, but
laterally), _Cercis_ (simple leaves; the corolla resembles that of
the Papilionaceæ, but the posterior petal is the smallest, and is
enveloped by the 2 lateral ones, which are enveloped in their turn by
the 2 anterior).--FRUIT INDEHISCENT: _Tamarindus indica_; the pod is
almost round, often a little abstricted between the seeds; the wall
is formed by a thin, brittle external layer, enclosing an acid pulp;
well-developed septa are present, between the seeds; the most internal
layer is parchment-like. Calyx 4-merous by the coalescence of 2 sepals.
Only 3 fertile stamens.--_Ceratonia siliqua_ (Carob-bean, Locusts);
the pod is long, compressed, with thick sutures, and has a wall, the
central part of which is more or less leathery, fleshy and sweet;
there are transverse septa between the seeds, as in the Tamarind.
Embryo greenish in endosperm. The flower is without a corolla, 5
stamens.--_Pterogyne_ (winged fruit), etc.--KRAMERIEÆ with _Krameria_
is an anomalous group.
DISTRIBUTION. 80 genera, with 740 species; almost exclusively
in the Tropics. The Carob-tree and _Cercis_ grow in the
Mediterranean basin. The largest and most widely distributed
genus is _Cassia_, which is found as trees, shrubs, and weeds
in all tropical countries. The order has many important
uses to mankind. MEDICINAL: the leaves and pods of _Cassia
acutifolia_ and _angustifolia_ (officinal, Senna-leaves),
the fruit-pulp of the _Cassia_-sub-genus, _Cathartocarpus_.
Rhatany root from _Krameria triandra_ (Peru, officinal).
_Balsam_ is extracted from a number of _Copaifera_-species
(Balsam of Copaiba) from S. Am. (officinal), and from _Hymenæa_
(Copal balsam), _Trachylobium_ and others. _Edible fruits_ are
obtained especially from the Carob-tree (from the East) and
the Tamarind (officinal). The heart-wood of several species of
_Cæsalpinia_, such as _C. brasiliensis_ (the Pernambuco-tree),
_echinata_ (Red-tree), and _sappan_, yield _dyes_; _Hæmatoxylon_
(_H. campechianum_, Logwood), _Copaifera bracteata_
(Amarant-tree).--_Timber_ is obtained from many (_Melanoxylon_
and others). In Europe they are of little importance as
ornamental plants, these being confined principally to the
species of _Gleditschia_ (_G. triacantha_, from N. Am.) and
_Cercis_ (the Judas-tree, _C. siliquastrum_, S. Eur.), which
are cultivated in gardens; but in tropical gardens beautiful
flowering species, _e.g._ of _Cassia_, _Poinciana_, _Brownea_,
are found, and the most beautiful of all ornamental plants, the
Indian _Amherstia nobilis_.
[Illustration: FIG. 511.--Diagram of _Faba vulgaris_: _f_ the
standard; _v_ the wings; _k_ the keel.]
Order 2. =Papilionaceæ.= The flower (Figs. 511, 512) is _strongly
zygomorphic_ and somewhat perigynous (Fig. 512 _B_; most frequently
more on one side than the other). The calyx is _gamosepalous_ and
persistent. The polypetalous corolla has _descending_ imbricate
æstivation, the posterior, large leaf, the _standard_ (Figs. 511 _f_;
512 _B’_, _e_), _covering in the bud_ the two lateral ones, the _wings_
(Figs. 511 _v_; 512 _B’_, _a_), which again cover the two anterior;
these are united in the form of a boat, the _keel_ (_k_ and _c_); the
wings and the two petals of the keel are very unsymmetrical. That the
keel is formed of two petals is seen by its position (in front of one
sepal) and by the two often more or less free claws. The 10 (5 + 5)
_stamens_ (monadelphous) _are either all united into one bundle, or
into two bundles_ (diadelphous), the posterior one being free (Fig. 512
_C_). The ovules are _curved_ and _also the embryo_ (Fig. 512 _G_),
especially the hypocotyl, so that the radicle assumes a position close
to the edge of the thick, fleshy cotyledons. Endosperm wanting; the
cotyledons are very rich in proteid reserve material. The forms of the
fruit and exceptions are described under the genera.
[Illustration: FIG. 512.--_Pisum sativum_: _A_ entire flower; _B_
in longitudinal section; _C_ gynœceum and stamens; _D_ gynœceum;
_B’_ corolla dissected, _e_ standard, _a_, _a_ wings, _c_ keel;
_D_ seed opened to show the cotyledons (_c_), the radicle (_r_),
the plumule (_g_); _E_ fruit (legume); _F_ seed.]
_Geocarpic_ fruits, _i.e._ those which penetrate the soil during
their development and ripen underground, are found in _e.g._
_Arachis hypogæa_ (see page 472), _Trifolium subterraneum_,
_Vicia amphicarpæa_. _Germination_ takes place in various ways.
In the majority the cotyledons are raised above the ground as
green, leaf-like bodies; in the Vicieæ they remain thick and
white, and are always enclosed in the testa, and are therefore
never able to take part in the work of assimilation; in species
of _Phaseolus_, on the other hand, they are raised well above
the ground and become green, but remain however thick and fleshy.
=1, 2.= The two groups PODALYRIEÆ (the majority of the genera
are Australian) and SOPHOREÆ (_Sophora_, _Edwardsia_, etc.),
represent the oldest type, as they have 10 _free stamens_ and so
form the transition to the Cæsalpiniaceæ. Nearly all are trees
and shrubs.
=3.= ASTRAGALEÆ. Herbs or shrubs, less frequently trees, with
_imparipinnate_ leaves (without tendrils). The flowers are
generally borne in racemes or spikes. Stamens monadelphous or
diadelphous.--_Astragalus_ (Milk-Vetch) has the legume incompletely
divided longitudinally into 2 loculi by a septum formed by the incurved
dorsal suture. Diadelphous.--_Glycyrrhiza_ (Liquorice); _Colutea_
(Bladder-Senna) from S. Europe; _Robinia_ (the false Acacia) with
thorny stipules; _Indigofera_ (the Indigo plant); _Amorpha_ (which has
only one petal, namely the standard, and the fruit a nut), _Caragana_,
_Wistaria_ (a climbing shrub), _Galega_. _Carmichælia australis_, when
old, produces flat branches with scale-like leaves.
=4.= VICIEÆ. _Climbing herbs_ with _paripinnate_ leaves, the midrib
ending in a point or frequently in a _tendril_, which generally is
branched, representing lateral veins without mesophyll; stamens
diadelphous; the cotyledons remain underground on germination.--_Vicia_
(Vetch) has a filamentous style, hairy towards the tip, and a
pod with many seeds; climbing by means of tendrils; the leaves
have many leaflets.--_Faba_ (_F. vulgaris_, Horse-bean) is erect,
without tendrils; its pod is thick with spongy septa between the
seeds.--_Ervum_ (Lentil) has a pod with only 1–2 seeds, and sweeping
hairs (stylar-brush) on the inner side of the style.--_Pisum_ (Pea;
Fig. 512) has very large stipules, the bent style has a hollow groove
on the anterior side. _P. sativum_ (Common Pea), _P. arvense_ (Grey
Pea).--_Lathyrus_ (Sweet Pea) generally has an angular, winged stem and
most frequently only a few pairs of leaflets. The style is flattened,
with sweeping hairs on the back. ~In _L. aphaca_ the stipules alone
are developed into foliage-leaves, while the remainder of the leaf is
modified into a tendril.~--_Cicer_ has a nearly straight embryo and
imparipinnate leaves with dentate or incised leaflets. _C. arietinus_
(Chick-pea).--~_Abrus_ (_precatorius_, etc.); the seeds (“Crab’s eyes,”
“Paternoster peas,” “Jequirity”) are scarlet with a black spot round
the hilum.~
=5.= PHASEOLEÆ. Herbs, twining or erect, but not climbing by tendrils;
the leaves are imparipinnate, generally _ternate_, and bear small,
linear bodies resembling stipules at the base of the stalks of the
leaflets. The inflorescences are most frequently compound, groups of
few flowers being situated on short, nodose, lateral axes borne on a
longer stem. On germination the cotyledons are raised a considerable
distance above the ground, and become greenish, but do not become
leaf-like; in _P. multiflorus_ they remain underground. Stamens as
in the Vetches.--_Phaseolus_ (Kidney-bean): the keel with the stamen
and style is spirally _twisted_ (to the right). Herbs, twining to the
left.--~The “Calabar-bean” (_Physostigma venenosum_), _Erythrina_,
_Clitoria_, _Glycine_, _Soja_, _Mucuna_, _Apios_, _Canavalia_, _Vigna_,
_Dolichos_, _Cajanus_, _Rhynchosia_, etc.~
=6.= TRIFOLIEÆ (CLOVERS). Herbs with _ternate_ leaves, the leaflets
are often dentate with the veins prolonged into the teeth; stamens
diadelphous; fruit 1-locular, 1–few-seeded, pyxidium-like, irregularly
dehiscent, or more frequently a _nut_. The flowers are generally borne
in capitula, racemes, or spikes.--_Trifolium_ (Clover). The corolla
is gamopetalous. The calyx persists, together with the corolla, round
the ripe fruit. The inflorescence is a spike, capitulum or capitate
umbel; the leaves are ternate, and have adnate stipules.--_Medicago_
(Medick). The corolla falls off after flowering; fruit curved like a
sickle or spirally twisted; it is a nut, and opens with difficulty.
Leaves ternate.--_Melilotus_ (Melilot) has a small, spherical or
lanceolate, thick and wrinkled fruit, which as a rule is indehiscent.
The inflorescence is a raceme, often long, or a spike, sometimes a
capitulum. Leaves ternate.--_Ononis_ (Rest-harrow) differs in having
monadelphous stamens and in being more shrub-like and bushy, and in
having a normal, 2-valved pod, by which characteristic it approaches
the Genisteæ. The flowers are generally rose-coloured, solitary, or in
few-flowered racemes in the leaf-axils. Thorns (branches) are often
present; the leaves are compound with only one small leaflet (the
terminal one), or ternate with adnate stipules.
=7.= LOTEÆ. Herbs with ternate or imparipinnate leaves, with entire
leaflets. In the latter case, when the lowest pair of leaflets is
placed quite close to the sheath, the stalk is wanting, and apparently
a trifoliate leaf with large stipules is developed. Flowers in
an umbel or capitulum. Stamens monadelphous or diadelphous, the
filaments (either all of them, or only the 5 sepal-stamens) are
widened at the top.--_Lotus_ (Bird’s-foot-trefoil) has a long, round
pod.--_Tetragonolobus._--_Anthyllis_ (Lady’s-finger); the fruit is
a nut, which is distributed by the wind by means of the membranous,
bladder-like calyx, which completely encloses and falls off with it.
=8.= GENISTEÆ. The majority are shrubs or trees with apparently simple
leaves, _i.e._ compound leaves with only one leaflet (the terminal
leaflet), or ternate leaves; the stipules in most instances are very
small or are entirely wanting; stamens monadelphous.--_Genista_
(Dyer’s-weed) has apparently simple leaves; the branches often
terminate in a thorn. ~The strongly-winged stems in _G. sagittalis_
are its most important organs of assimilation. _Bossiæa rufa_
has flat branches, its leaves being reduced to small, pointed
stipules.~--_Sarothamnus_ (Broom) has switch-like, angular branches
and often both the apparently simple and ternate leaves on the same
shoot; style spirally rolled.--_Cytisus_ (Laburnum). _Ulex_ (Furze;
~in _U. europæus_, the seedlings bear a few foliage leaves, but
the leaves succeeding these are modified into thorns~); _Spartium_;
_Crotalaria_, etc.--_Lupinus_ (Lupin) is allied to this group; it has
a thick, often somewhat fleshy pod, and digitate leaves with adnate
stipules.--_Retama._
=9.= HEDYSAREÆ are especially recognised by having the ovary divided
by transverse septa into as many cells as there are seeds, the fruit
thus becomes a _lomentum_, dehiscing transversely into nut-like joints
(Fig. 513).--_Ornithopus_ (Bird’s-foot); _Coronilla_; _Hippocrepis_;
_Onobrychis_ (Sainfoin) has a fruit with only 1 joint (_i.e._ a
1-seeded nut); _Desmodium_; _Alhagi_; _Hedysarum_, etc.--_Arachis
hypogæa_ (Earth-nut) has a pod which is abstricted between the seeds,
and is indehiscent, but is not multilocular nor a true lomentum; it is
reticulately wrinkled externally, and ripens underground; the basal
part of the ovary is prolonged after flowering, attaining a length of
several inches, and buries the young fruit in the soil. The embryo is
straight.--~_Desmodium gyrans_ is well-known for its motile leaflets.~
[Illustration: FIG. 513.--_Hedysarum coronarium._]
=10.= DALBERGIEÆ. 25 genera; especially in Tropical America; the
majority are trees, a few shrubs or lianes; the leaves are simple
or imparipinnate. The fruit is _indehiscent_ in all; in some it is
a winged, in others a wingless _nut_ (_Machærium_, _Dalbergia_,
_Centrolobium_, etc.), in others, again, a drupe, _e.g._ in _Dipteryx_
(Tonquin-bean) and _Andira_. In some genera the embryo is straight.
POLLINATION. Especially effected by Bees. The nectar is secreted
by a ring or disc-like portion round the base of the gynœceum or
the inner surface of the receptacle. The flower is constructed
with a peculiar mechanism to ensure cross-pollination by
insects. The pollen is shed just before the flower opens, and
is retained in a pouch formed by the keel. An insect visiting
the flower uses the wings and keel for a landing-stage, and
in attempting to reach the honey presses down the wings and
the keel which are locked together near the standard; the
stylar-brush by this means is forced through the apical opening
of the keel and a little pollen is thus swept out and deposited
upon the abdomen of the visiting insect as it presses against
the apex of the keel; the insect thus carries away pollen and
may effect cross-pollination. In the different flowers this
arrangement is modified in various ways to promote pollination.
5000 species (319 genera); especially in the Tropics, where
many are important forest trees.--The following plants are used
FOR FOOD: _Pisum sativum_ (W. Asia?) and _arvense_ (Italy);
_Phaseolus vulgaris_ (Kidney-bean, American; _Dolichos sinensis_
was known to the Greeks and Romans under the name “φασηλος,”
“phaseolus”), _P. compressus_ (French-bean), etc.; _Faba_
_vulgaris_ (Field-bean, Horse-bean; from the Old World);
_Ervum lens_ (Lentil, Eastern Mediterranean); in tropical
countries the oil-containing seeds of _Arachis hypogæa_.--The
following are FODDER plants: _Vicia sativa_, _Faba vulgaris_,
_Onobrychis sativa_ (Sainfoin), _Medicago sativa_ (Lucerne),
and _lupulina_ (Medick), species of _Trifolium_, _Hedysarum
coronarium_. OFFICINAL: “Liquorice root,” from _Glycyrrhiza
glabra_ (S. Europe); “Red Sandalwood,” from _Pterocarpus
santalinus_ (Tropical E. Asia); Gum Tragacanth, from
_Astragalus_-species (E. Mediterranean); Balsam of Peru, from
_Toluifera pereiræ_, and Balsam of Tolu, from _Toluifera
balsamum_. Calabar-beans, from _Physostigma venenosum_; Kino,
from _Pterocarpus marsupium_; the pith of _Andira araroba_ is
used under the name of “Chrysarobin.”--Of use TECHNICALLY:
_Genista tinctoria_ (yellow dye) and _Indigofera-species_
(Indigo), the bast of _Crotalaria juncea_ (Sunn Hemp); the
seeds of _Dipteryx_, which contain Coumarin, and are highly
scented, and Balsam of _Myroxylon_. POISONOUS: the seeds of
_Laburnum_ (_Cytisus laburnum_), various species of _Lathyrus_,
and _Abrus precatorius_; the latter contain two poisonous
proteids, paraglobulin and albumose, which resemble snake-poison
in their effects. The following are ORNAMENTAL plants:
_Phaseolus multiflorus_ (Scarlet runner, from America), _Robinia
pseudacacia_, _Amorpha_, _Colutea_, _Coronilla_, _Indigofera
dosua_, _Wistaria polystachya_, _Cytisus laburnum_ (Laburnum, S.
Europe, Orient.) and other species.
Order 3. =Mimosaceæ.= The flowers are most frequently hypogynous
and _regular_, the æstivation of the corolla is _valvate_ and, in
the majority of instances, that of the calyx also. The flower is
4-merous, less frequently 5- or 3-merous.--The flowers are generally
small, but are always borne in compact, round _capitula_ or spikes
(Fig. 514); they are hypogynous or perigynous. The calyx is generally
_gamosepalous_ and the corolla _gamopetalous_, the latter being
frequently wanting. The stamens are equal or double the number of the
petals (_Mimosa_, etc., in _M. pudica_, _e.g._ S4, P4, A4, G1) or
(in _Acacia_, _Inga_, etc.) in a large, indefinite number, free or
monadelphous, often united to the corolla (Fig. 514 _b_). The colour of
the flower in most cases is due to the long and numerous stamens. The
_fruit_ is various. The embryo is _straight_ as in the Cæsalpiniaceæ.
_Entada_ and many species of _Mimosa_ have a flat, straight, or
somewhat sickle-like pod, which resembles the siliqua of the Cruciferæ
in that the sutures (in this instance, however, dorsal and ventral
suture) persist as a frame, but the intermediate portion divides, as
in the transversely divided siliqua, into as many nut-like portions as
there are seeds. Some species have a pod of enormous dimensions. The
seeds of _Entada gigalobium_ are often carried from the West Indies to
the N. W. coasts of Europe by the Gulf Stream.--The fruit of _Acacia_
in some species is an ordinary pod, in others it is transversely
divided, or remains an undivided fruit, a nut.--This order includes
both trees and herbaceous plants, which are often thorny; the leaves
are usually bipinnate (Fig. 514) and are sensitive, and also possess
sleep-movements.--Many Australian Acacias have compound leaves only
when young, but when old have _phyllodia_, _i.e._ leaf-like petioles
without blades, placed vertically. A large number have thorny stipules,
which in some (_Acacia sphærocephala_) attain an enormous size, and
serve as a home for ants, which in return protect their host-plant
against the attacks of other, leaf-cutting ants.
[Illustration: FIG. 514.--_Acacia farnesiana_: _a_
inflorescence; _b_ flower.]
Other genera besides those mentioned are: _Adenanthera_, _Desmanthus_,
_Parkia_, _Inga_ (with rather fleshy, indehiscent fruit), _Calliandra_,
etc.
1350 species (30 genera); none natives of Europe, their home
being the Tropics and sub-tropical regions, especially
Australia and Africa.--Fossils in Tertiary.--Gums are found in
many species of _Acacia_, especially the African (Gum arabic)
and Australian, of which some are _officinal_. The bark, and
also the fruits, contain a large amount of _tannic acid_ and
are used as astringents and in tanning (“Bablah” is the fruits
of several species of _Acacia_). Catechu is a valuable tanning
material extracted from the wood of _Acacia catechu_ (E. Ind).
The flowers of _Acacia farnesiana_ (Fig. 514) are used in
the manufacture of perfumes. With us they are cultivated as
ornamental plants, _e.g._ _A. lophantha_ and many others, in
conservatories.