A. STAMENS 5. 1, Gentianaceæ; 2, Apocynaceæ; 3, Asclepiadaceæ;
4, Loganiaceæ.
B. STAMENS 2. 5, Oleaceæ; 6, Jasminaceæ; 7, Salvadoraceæ.
Order 1. =Gentianaceæ= (=Gentians=). _Glabrous_ herbs, without latex;
the opposite, undivided and _entire_ leaves are often slightly united
at the base; many have rosette-like radical leaves. _Stipules absent_.
The flowers are generally borne in regular, dichotomously-branched
_dichasia_ (Figs. 580, 581 _A_), which finally become transformed into
unipared scorpioid cymes; the parts of the flower are 4–5-merous as
far as the gynœceum, which is 2-merous; the calyx frequently is almost
polysepalous; the corolla has distinctly twisted æstivation (the upper
edges being free) (Fig. 581 _A_), except _Menyantheæ_. The carpels are
_entirely_ united, and most frequently form a _1-locular_ ovary with 2
_parietal placentæ_ bearing many ovules (often in several rows, Fig.
581 _D_, _F_). _Capsule_, 2-valved, with septicidal dehiscence, the
incurved edges bearing the seeds (Fig. 581 _D_, _F_).
[Illustration: FIG. 580.--_Erythræa._ Inflorescence. 1, 2, 3,
etc., the successive shoot-generations.]
=1.= GENTIANEÆ.--_Gentiana_ (Gentian) has most frequently a tubular,
campanulate or funnel-shaped corolla, sometimes with teeth between the
corolla-lobes and fringed in the throat of the corolla; _G. lutea_ has
a rotate, yellow corolla.--~_Swertia_: rotate corolla; each lobe has at
its base 1–2 nectaries, with fringed edges.~
_Erythræa_ (Centaury, Fig. 581); corolla most frequently salver-shaped.
The anthers ultimately become spirally twisted (_E_). The style
prolonged, deciduous. The flower has the _Lobelia_-arrangement,
_i.e._ the median sepal is anterior; the corolla is rose-coloured (in
the native species). The capsule is semi-bilocular (Fig. 581 _F_,
_G_).--~_Cicendia_ has a low creeping stem, fine as a thread, and
small, yellow flowers, 4-merous (without twisted anther).--_Chlora_
(Yellow-wort) 6–8-merous.~
[Illustration: FIG. 581.--_Erythræa centaurium._ Inflorescence,
flower and fruit: _br^1_, _br^2_ floral-leaves of the 1st and 2nd
order; _G_ a valve of the capsule separated from its fellow.]
=2.= MENYANTHEÆ. _Menyanthes_ (Buck-bean) deviates in several respects
from the type of the order. The leaves are _scattered_ and, in _M.
trifoliata_, trifoliate; the corolla has _valvate_ æstivation; the
testa is also very hard (thin in the true Gentians). They are aquatic
plants with creeping rhizome; the flowers borne in racemes, with
terminal flower, heterostylous. The corolla is funnel-shaped with a
very hairy throat.--~_Limnanthemum_ with floating leaves, like the
Water-lilies.~
575 species; distributed over the entire globe, but most
numerous in _Alpine_ districts. Neither poisonous nor nutritive
plants are found, but several are used in medicine on account of
the _bitter_ properties so prevalent amongst them. OFFICINAL:
the roots of _Gentiana lutea_. The roots of other species,
_e.g._ _G. purpurea_, _punctata_ and _pannonica_ (Europe) and
the leaves of _Menyanthes trifoliata_ are medicinal. Some are
grown as ornamental plants on account of the pure (often deep
blue) colour of the flowers.
Order 2. =Apocynaceæ= (=Periwinkles=). Trees and shrubs (also lianes),
less frequently herbs, generally _with latex_. The leaves are
opposite, simple, entire, _without stipules_; the flowers are regular;
corolla-lobes oblique, æstivation twisted. The stamens are individually
free, and the _pollen-grains are free_ or at most united in fours (see
Asclepiadaceæ). The two carpels have 2–∞ ovules, in all cases there is
only 1 style and a capitate stigma, which towards the base is widened
out into a disc-like table (stigma-disc) abstricted in the centre;
but the carpels in most of the genera (_e.g._ those mentioned below)
are entirely separate, and the fruit consists of two _follicles_, the
seeds of which often have a tuft of _woolly hairs_ projecting from the
micropyle, less frequently of two drupes. In some other genera there
is a 1-locular (provided with 2 parietal placentæ) or a 2-locular ovary
becoming a 2-valved capsule or a berry. Endosperm abundant.
_Vinca_ (Periwinkle) has a salver-shaped corolla, which is twisted
to the left in æstivation (_i.e._ the left edge of the petals is
free); nectaries 2, alternating with the carpels; the summit of the
style is hairy. Follicles; seeds without hairs. ~Mostly creeping,
perennial, evergreen plants, whose large flowers are apparently
axillary; in reality they are terminal, but by the development of
the bud in the axil of one of the two uppermost leaves, they are
thus displaced over the other leaf of the pair (a helicoid sympodium
being formed).--_Plumeria_, _Tabernæmontana_, _Cerbera_ (drupe).
_Aspidosperma._~
_Nerium_ (Oleander). The leaves are in whorls of 3. Corolla
funnel-shaped, in æstivation twisted to the right, and with a corona
resembling that of _Lychnis_. The anthers are prolonged at the base
and each also bears at the apex a long, linear, hairy appendage; these
finally become spirally twisted. Follicles; seeds hairy. _Apocynum_,
_Echites_, etc. _Epigynum_ is epigynous.
124 genera, 1,000 species; principally in the Tropics. Only 2
species of _Vinca_ are natives of this country; the following
are cultivated as ornamental plants:--_Vinca minor_, _V. major_,
_V. (Lochnera) rosea_, _Amsonia salicifolia_, _Nerium oleander_
(Eastern Mediterranean). The _latex_ of some is _poisonous_
(_Tanghinia venenifera_, _Cerbera_). Caoutchouc is obtained from
others (_Hankornia_, _Landolphia_, _Vahea_, etc.). Tough bast is
frequently developed. The bark of _Aspidosperma quebracho_ and
the seeds of _Strophanthus hispidus_ are used in medicine (also
for African arrow-poison), the latter is officinal.
Order 3. =Asclepiadaceæ.= A natural and easily recognised order,
closely allied to the Apocynaceæ, having, like it, frequently a
poisonous latex, opposite, single, entire leaves and fundamentally the
same floral diagram and floral structure (S5, P5, A5, G2); but in some
the æstivation of the corolla is valvate. The carpels here also have
_free ovaries_, but are united for some distance above into a _large,
shield-like, 5-angular head_, having on its underside the true stigmas,
and the fruit always consists of 2 _follicles_; seeds most frequently
numerous and _hairy_ at the micropyle (“vegetable silk”); endosperm
scanty.--The order is distinguished from the Apocynaceæ and from all
other plants also, except the Orchids, by having all the pollen-grains
in each of the =2= loculi of the anthers (true 2-locular anthers)
united into _one waxy, club-shaped pollen-mass_ (“pollinium”), for the
purpose of pollination by insects. These heavy masses, in order to
secure pollination (as in the case of the Orchids), must be attached to
sticky discs (corpuscula); there are 5 corpuscula, one at each of the
corners of the 5-angular stylar-head (alternating with the anthers),
and to each of these are attached 2 pollinia, one from each of the
anthers situated on either side (thus each anther gives its right
pollinium to one corpusculum and its left to another). The stamens are
frequently united at the base, and each bears on the back a variously
formed, petaloid appendage, termed a “cucullus.”
[Illustration: FIG. 582.--_Asclepias cornuti._ _A_ An open flower
with the calyx (_k_) and corolla (_c_) turned down; the stamens
are bent together and surround the gynœceum. _B_ The andrœcium
after removal of the sterile part (cucullus) of the anther, which
functions as a nectary: _e_ the lateral expansions of the fertile
portion of the anthers; _f_ the slit between the expansions of
two contiguous anthers, through which the insect’s foot, and
later a pollinium which is caught by it, is dragged, and behind
which the only receptive part (stigma) is hidden; above the slit
_f_ is the gland (_r_), which secretes the horny corpusculum,
which is split at its base and joined on either side with a
pollinium (this is more distinctly seen in _D_ and _E_). When
the foot of the insect is caught in the slit (_f_) and is drawn
upwards, it becomes entrapped in the slit of the corpusculum,
which is then pulled out together with the pollinia firmly
attached to it. In walking over the flowers the insect will draw
its foot through other slits (_f_) and so leave the pollinia on
the stigmas. _C_, _D_ The gynœceum with the pollinia hanging
freely. _E_ A corpusculum and two pollinia.]
A peculiar relative position (and therefore a good, distinctive
characteristic) is often found in the _inflorescence_, which is cymose;
it is placed _between_ the two leaves of a whorl, nearer to one than to
the other. ~The leaf-pairs are placed obliquely in the floral region,
at acute and obtuse angles, and not at right angles (as in the purely
vegetative parts); the inflorescences are placed in two rows only which
are nearly 90° from each other, and the two contiguous to one another
are antidromous; they are in reality terminal, each on its own axis,
and the entire floral portion of the shoot is a unipared scorpioid
cymose sympodium; in addition, complications also arise through
individual parts becoming united.--Herbs and shrubs, some twining or
climbing.~
In _Asclepias_ the corolla is bent back and there is a cup-like
cucullus, from the base of which protrudes a horn-shaped body, bent
inwards.--_Vincetoxicum_ has a rotate corolla and a ring-like, 5-lobed
cucullus, without internal prominences.--~_Stapelia_ (especially from
S. Africa) is remarkable on account of its Cactus-like, leafless stems
and large, brownish flowers, often with carrion-like smell. _Periploca_
has more powdery pollinia (S. Eur., etc.); _Hoya carnosa_ (Wax-flower;
Trop. Asia) is a climber, and has small, annual, flower-bearing
dwarf-branches. _Ceropegia._~
201 genera with 1700 species, distributed over all tropical
countries; few outside these limits: no native species. Several
are used in medicine on account of the pungent properties of the
latex. Condurango-bark of _Gonolobus condurango_ is medicinal.
Caoutchouc is obtained from the latex of some (_e.g._ from
_Cynanchum_). The seed-hairs, which are most frequently shining,
silk-like, and white, are not sufficiently pliant to be of much
value. Ornamental plants in our gardens: _Asclepias_-species,
etc.
Order 4. =Loganiaceæ.= Ovary single, with two loculi, in
structure resembling the Rubiaceæ, but superior. 360 species
are included in this order; the majority are tree-like, some
lianes which climb by tendril-like branches. The _interpetiolar
stipules_ of some species are very characteristic (as in
Rubiaceæ, to which they maybe considered to be closely related).
The fruit is a capsule or berry. The most familiar genus
is _Strychnos_, which has spherical berries with an often
firm external layer, and compressed seeds with shield-like
attachments; endosperm abundant. The leaves have 3–5 strong,
curved nerves proceeding from the base.--_Spigelia._--They
have _no latex_, as in the two preceding orders, but many are
_very poisonous_ (containing the alkaloid “strychnine,” etc.);
the South American arrow-poison, urare or curare, is made from
various species of _Strychnos_, also an arrow-poison in the East
Indian Islands (Java, etc.). OFFICINAL, the seeds of _Strychnos
nux vomica_ (“Vomic nut,” Ind.). The seeds of _Strychnos
ignatii_ (Ignatius-beans, medicinal), and others are poisonous.
Order 5. =Oleaceæ.= The leaves are always opposite. The inflorescences
are racemes or panicles. The calyx and corolla are _4-merous_,
more or less united, free in some species; the corolla has most
frequently _valvate_ æstivation. All four forms of fruit occur (see
the genera). _Ovules pendulous_, 2 in each loculus (Fig. 583 _C_).
Endosperm oily.--_Syringa_ (Lilac) and _Forsythia_ (anthers somewhat
extrose) have _capsules_ with loculicidal dehiscence and winged
seeds.--_Fraxinus_ (Ash) has _winged nuts_ (samara) (Fig. 583 _D_);
trees with most frequently imparipinnate leaves; the flowers are
_naked_ and sometimes unisexual (polygamous), the Manna Ash (_F.
ornus_) has however a double perianth with 4 free petals (Fig. 583
_a_); in the native species, _F. excelsior_, the flowers open before
the foliage appears.--_Ligustrum_ (Privet) has _berries_.--_Olea_ (_O.
europæa_; Olive) has _drupes_; the pulp and seeds of the ellipsoidal
fruits are rich in oil. The lanceolate leaves are grey on the under
surface, being covered with stellate hairs. In the wild state it is
thorny (modified branches).--_Phillyrea_; _Chionanthus_.--Few species
of _Linociera_ have 4 stamens.
[Illustration: FIG. 583.--_Fraxinus ornus_: _A_ flower; _ca_
calyx; co corolla; _B_ gynœceum and calyx; _C_ longitudinal
median section of gynœceum; _D_ fruit.]
180 species; chiefly in the northern temperate zone. The
_Olive-tree_ (_Olea europæa_) has been an important cultivated
plant from ancient times (Olive oil, Provence oil, “Sweet oil”).
The best oil is extracted from the fruit-pulp. The fruits are
edible. Home: Western Asia, Eastern Mediterranean. TIMBER:
the Ash (_Fr. excelsior_). OFFICINAL: the Manna Ash (_Fr.
ornus_), cultivated in the Mediterranean countries for the
sake of its saccharine juice, which flows out and coagulates
into “Manna.”--The following are ornamental plants: species of
_Ligustrum_ and _Syringa_ (introduced in the 16th century, from
S.E. Europe and Asia), _Forsythia_ (China, Japan; the large,
yellow flowers are borne on dwarf-branches with scale-like
leaves, before the opening of the foliage-leaves), _Chionanthus_.
Order 6. =Jasminaceæ.= The æstivation of the corolla is
_imbricate_; the _ovules are erect_; seeds almost without
endosperm; radicle directed downwards. The number of lobes
in the calyx and corolla is not 4, but _e.g._ 5, 8, 10,
and variations are sometimes found in the same individual.
The fruit is a berry or capsule. Many species are twiners,
and their scattered or opposite leaves are most frequently
imparipinnate.--120 species; especially in Trop. Asia (E.
India). Some _Jasminum_-species are cultivated as ornamental
shrubs in the warmer districts on account of their elegant
foliage, and beautiful, sweet-scented flowers, the essential
oil of which is also used in perfumery; the best known are: _J.
sambac_ and _grandiflorum_. _Nyctanthes arbor-tristis_ opens its
sweet-scented flowers only at night (E. India).
Order 7 (?). _Salvadoraceæ._ 8–9 species; Asia,
Africa.--_Salvadora._
b. Tetracyclicæ with epigynous flowers.