The chief characteristics of the orders belonging to this family are
the ☿, regular, generally 5-merous, _hypogynous_ flowers with 5-merous
_calyx_, sepals united and _valvate_ in the bud; petals 5, free (often
_twisted_ in the bud); stamens ∞ _e.g._: 10, in two whorls, but one of
these is more or less suppressed, often altogether wanting, or replaced
by 5 staminodes, while _the other_ (inner whorl) _is generally divided
more or less deeply_ into a large number of anther-bearing filaments.
The filaments too (except _Tiliaceæ_) are _united into a tube_, which,
especially in the _Malvaceæ_, forms a long column in the centre of
the flower, surrounding the gynœceum (Figs. 445, 448); in this case,
which is the most pronounced, the filaments are united into one bundle
(_monadelphous_), in other instances, _polyadelphous_. The number of
carpels varies greatly (2 to about 50), but they are nearly always
united and form a syncarpous multilocular gynœceum.--The vegetative
characters also closely agree, the leaves _are always scattered and
generally stipulate_; all the green portions very often bear _stellate
hairs_, and the bark in all the 3 orders is _rich in tough bast_.
Mucilage is often present in cells or passages.--This family is
connected with the _Ternstrœmiaceæ_, from which it is very hard to draw
a sharp line of demarcation, and it is also allied to the _Cistaceæ_
and to the _Gruinales_.
Order 1. =Sterculiaceæ= (including Buettneriaceæ). This is, no
doubt, the least modified order, and one in which the stamens occur
undivided. Obdiplostemonous. The 10 stamens in two whorls are most
frequently united at the base into a short tube, and have _4-locular,
extrorse_ anthers. The calyx-stamens are nearly always simple,
tooth-like staminodes, situated on the edge of the tube, or are
entirely suppressed. The same relation is found, for instance, in the
Ampelidaceæ and Rhamnaceæ, namely _5 stamens in front of the 5 petals_;
not infrequently the 5 stamens are doubled (Fig. 441). Unisexual
flowers are found in _Sterculia_, _Cola_, _Heritiera_. The corolla
is often wanting, or developed in an unusual manner. Each loculus of
the ovary (generally 5) always contains more than one ovule. Fruit a
capsule. Androgynophore often present (_Helicteres_; _Sterculia_, etc.).
_Hermannia_, _Mahernia_, _Melochia_, etc., have flat petals
with twisted æstivation; 5 undivided stamens, which usually
are but slightly united at the base, and most frequently,
without staminodes. _Thomasia_; _Helicteres_; _Sterculia_
(free follicles).--_Theobroma_, _Rulingia_, _Buettneria_,
_Commersonia_, _Guazuma_, etc., have petals concave at the
base, and terminating in a limb abruptly bent back, and at the
boundary between them most frequently ligular outgrowths, as in
certain genera of the Caryophyllaceæ; stamens 5–15–∞, anthers
at the edge of a short tube and 5 linear staminodes (Fig.
441).--The Cocoa-tree (_Theobroma_), (Fig. 440) bears large,
reddish-yellow, berry-like fruits, resembling short cucumbers,
but ultimately becoming leathery to woody; in each of the 5
loculi are 2 (apparently only 1) rows of horizontal, oily seeds,
as large as almonds. Cotyledons large, thick, and irregularly
folded. Endosperm absent (Fig. 442).
49 genera, with about 750 species; almost entirely confined
to the Tropics; none in Europe or in N. Asia.--The seeds
of the Cocoa-tree (_T. cacao_, _bicolor_, _glaucum_, etc.,
natives of Trop. Am., especially north of the Equator) are
used for chocolate and are also _officinal_ (“Cocoa-beans,”
“Cocoa-butter,” “Oil of Theobroma”). Theobromine. _Cola
acuminata_, Africa.
[Illustration: FIG. 440.--_Theobroma cacao._ Branch with flowers
and fruits (⅙).]
[Illustration: FIGS. 441–442.--_Theobroma cacao._
FIG. 441.--Diagram of the flower: _st_ barren stamens.
FIG. 442.--_B_ Seed in transverse section: _n_ hilum. _A_ Embryo
after the removal of one of the cotyledons.]
Order 2. =Tiliaceæ.= This differs from the other orders of the
Columniferæ chiefly in the stamens being entirely _free_ from each
other, and also _divided_ into many filaments, _as far as the base_,
or at all events very far down, so that the _flower appears to have
numerous stamens_ or to be _slightly_ polyadelphous (Fig. 443); in
addition to this, it may be observed that the anthers are _4-locular_
and _introrse_. In _Luehea_ the groups of stamens alternate with the
petals. In a few genera (_Corchorus_, _Triumfetta_) 10 free and single
stamens are found in 2 whorls; but, in the majority, groups of free
stamens in separate bundles. The stamens are more or less united
in _Apeiba, Luehea_. Style simple. Ovary 2-locular. The ovules are
pendulous; raphe turned inwards. The calyx readily falls off; the
æstivation of the entirely free petals is slightly imbricate (_not
twisted_).
[Illustration: FIG. 443.--Inflorescence of _Tilia_, with
its winged bracteole (_h_); _a_, _a_ axis of the shoot; the
vegetative bud is seen between the inflorescence and the axis of
the shoot; _b_ petiole of foliage-leaf.]
_Tilia_ (Figs. 443, 444). Calyx and corolla 5-merous; the 5 staminal
leaves (opposite the petals) divided as far as the base into a large
number of stamens which are free or united into groups; gynœceum with
5 loculi in the ovary (opposite the sepals); there are 2 ovules in
each loculus, though the ovary ripens into a 1-seeded nut, which is
not detached from the axis of the inflorescence, but is carried away
by the wind, whirling round and round, its large-winged bracteole
serving as a parachute (Fig. 443).--~Only trees, with alternate,
obliquely heart-shaped and dentate leaves; stellate hairs, as in the
other Columniferæ, are often present. The terminal bud of the branch
always fails to develop, and the growth is then continued sympodially
by the uppermost axillary buds. The INFLORESCENCE (Figs. 443, 444) is
a 3–7-flowered dichasium (Fig. 444 _t_, _d_, _e_), which is developed
in the axil of a foliage-leaf (Fig. 444). The first of its 2 bracteoles
(_a_) is large, thin, leaf-like, and united with the inflorescence,
the lower portion of which forms a broad wing, its so-called “bract”;
the second bracteole (_b_), on the other hand, remains scale-like,
and supports a winter foliage-bud covered with bud-scales which thus
is situated at the base of the inflorescence, and is a bud of the
2nd order, in relation to the vegetative shoot. This bud is always
found beneath the inflorescence on the branch placed horizontally,
and the winged bracteole is always found above it, a relation which
is connected with the fact that the 2 rows of shoots on the sides
of a branch are _antidromous_ with regard to each other.--The
dichasium itself (Fig. 444) terminates with the flower (_t_); it has
3 floral-leaves (_c_, _d_, _e_), which soon fall off; _c_ is barren:
the other two bear flowers, or few-flowered dichasia, or unipared
scorpioid cymes (indicated in the figure).--The foliage-leaves are
folded in the bud upon the median line (1, 2, 3 in Fig. 444 are
foliage-leaves with their 2 stipules), the inner half is broader than
the outer, and after unfolding is turned away from the mother-axis (the
position of the new inflorescences and vegetative buds is indicated in
their axils on the figure).--The cotyledons on germination appear above
the ground as large, _lobed_ leaves.~
Of the other genera some have a bell-shaped, gamosepalous
calyx, some have no corolla, the anthers of some open at the
apex (_Aristotelia_, _Elæocarpus_, etc.), the majority have
a capsule, some have berries, or drupes, some separate into
fruitlets, etc.--_Corchorus_, _Triumfetta_ (nut, with hooked
bristles), _Luehea_, _Apeiba_, etc. _Sparmannia_ is an African
genus; 4-merous flowers; fruit a warted capsule; filaments
numerous and sensitive to touch, the external ones are without
anthers and moniliform above. The plant is covered with numerous
soft and stellate hairs, and at the apex of the branches bears
several cymose umbels.
[Illustration: FIG. 444.--Diagram of the inflorescence of _Tilia_
and the vegetative bud; the position of the leaves is indicated,
and also the position of the inflorescences, which develop from
their axils in the following year.]
POLLINATION in _Tilia_ is effected by insects, especially
bees and Diptera, which swarm round the tree tops, allured
by the numerous strongly-scented flowers and the easily
accessible honey (formed in the hollow sepals). As the flowers
are pendulous, the nectar is protected from ruin; and, in
addition, the inflorescence is more or less concealed beneath
the foliage-leaf. Self-pollination is impossible, on account of
protandry.--About 470 species (nearly all trees and shrubs);
especially in the Tropics, only a few being found in the
temperate, none in the polar regions, or in high mountainous
districts.--The inflorescence of the native species of _Tilia_
is medicinal. The wood is used for charcoal.--The majority are
used for timber, and for the sake of the bast (“Bast,” “Jute,”
the bast of _Corchorus textilis_, _Luehea_, and others).
Order 3. =Malvaceæ= (=Mallows=). The plants are easily recognised by
the scattered, simple, _palminerved_, most frequently lobed, stipulate
_leaves_, folded in the bud; the perfect, regular, hypogynous flowers,
with _gamosepalous_, persistent, 5-merous calyx with _valvate_
æstivation; the 5 _petals twisted_ in the bud and united with one
another at the base, and by the 5 _apparently numerous stamens_ (Figs.
445, 448), with the filaments _united into a tube_, with _reniform
bilocular anthers_ opening by a crescentic slit (in 2 valves).
Carpels 3–∞ united into one gynœceum; the _embryo is curved and the
cotyledons are folded_ (Figs. 447, 451); endosperm scanty, often
mucilaginous.--Most of the plants belonging to this order are herbs,
often closely studded with _stellate hairs_. The leaves are most
frequently palmatifid or palmatisect.
[Illustration: FIG. 445.--Longitudinal section through the flower
of _Malva silvestris_.]
[Illustration: FIG. 446.--Diagram of _Althæa rosea_: _i_ the
epicalyx.]
An _epicalyx_ is often found formed by _floral-leaves_ placed
close beneath the calyx, in some 3, in others several. The
median sepal is posterior in the species without epicalyx,
often anterior in those which have an epicalyx.--The petals are
_twisted either to the right or to the left_ in accordance with
the spiral of the calyx; they are most frequently oblique, as
in the other plants with twisted corollas, so that the portion
covered in the æstivation is the most developed. The corolla
drops off as a whole, united with the staminal tube.--Only
the 5 petal-stamens are developed, but they are divided into
a number of stamens, placed in 2 rows, and provided only with
_half_-anthers (leaf-segments, see Fig. 446; the sepal-stamens
are completely suppressed); these 5 staminal leaves are then
united into a tube, frequently 5-dentate at the top, and
bearing the anthers on its external side. The pollen-grains
are specially large, spherical and spiny. There are from 3 to
about 50 carpels united into one gynœceum and placed round the
summit of the axis which most frequently projects between them.
There is only 1 style, which is generally divided into as many
stigma-bearing branches as there are carpels (Figs. 445, 448).
The fruit is a schizocarp or capsule. Endosperm (Figs. 447 A,
451) scanty, often mucilaginous round the _embryo_, which is
rich in oil.
The order is the most advanced type of Columniferæ; it stands
especially near to the Sterculiaceæ, but is separated from these
and from the Tiliaceæ, among other characters, by its 2-locular
(ultimately 1-chambered) anthers.