_Trees_ and _shrubs_ with small, unisexual, _monœcious_ flowers, having
no perianth or a simple inconspicuous one. The ♂ and ♀ flowers are
very different and generally placed in separate inflorescences. The
♂-flowers are most often adnate to the bracts. The stamens are placed
_opposite the perianth-leaves_, when they are present in equal numbers.
The ♀-flower is _naked_, or has a _superior_ perianth. The ovary at
the base is 2- or 3-(-6) locular with 1 or 2 pendulous ovules in each
loculus, only one of which is developed; the fruit is a one-seeded
_nut_; _endosperm absent_; embryo straight. The inflorescences, which
are either compound and mixed (small dichasia in spikes) or simple,
are here also termed _catkins_; but, strictly speaking, this term is
applied to the ♂-inflorescences only. In all Quercifloræ the leaves are
_scattered_ (usually in 2 rows) _simple_, and _penninerved_, and with
_deciduous stipules_.
It is worthy of remark that in _Betulaceæ_, _Corylaceæ_ and
_Quercus_ the ovules, and to some extent the loculi of the
ovary are not developed till after pollination, so that the
development of the pollen-tube proceeds very slowly. The
smallness of the flowers, the absence of honey, the dryness
and lightness of the pollen, the size of the stigma and the
abundance of hairs found on many stigmas are all adaptations for
wind-pollination. It is also an advantage that the flowers are
generally pollinated before the foliage-leaves are developed,
thus preventing the pollen being entangled by the leaves.
The two orders _Betulaceæ_ and _Corylaceæ_ mentioned here are
by other authors united into one order. [It is doubtful whether
these two should be retained in the family Quercifloræ, as
recent researches (p. 273) have shown that they differ from
the Cupuliferæ in many important points, and agree with the
Casuarinas in the fact that the pollen-tube enters the ovule
through the chalaza.]
Order 1. =Betulaceæ= (=Birches=). Monœcious, with thick, cylindrical,
_compound_ ♂ and ♀ inflorescences (2- or 3-flowered dichasia in a spike
with spirally-placed floral-leaves) (Figs. 324, 326, 328). When the
perianth in the ♂-flower is completely developed, it is composed of 4
somewhat united leaves, which are placed opposite the 4 stamens (Figs.
325, 326 _A_). The female flowers are _naked_; the ovary is bilocular,
with two styles and one _pendulous_ ovule in each loculus. The
subtending floral-leaves unite with the bracteoles and form a 3–5-lobed
cover-scale, which is not attached to the fruit (Figs. 325 _D_, 326
_B_). Fruit a _nut without cupule_ (see _Corylaceæ_ and _Cupuliferæ_).
~In the bud the leaves are flat. The stipules are deciduous. On
germination the cotyledons are raised above the ground. Terminal buds
are only found on old Alder trees; the Birch has sympodial branches.~
[Illustration: FIG. 324.--_Alnus glutinosus._ Branch of Alder
with ♂-(_n_) and ♀-(_m_) catkins: _k_ bud; _b_ fruit-bearing
catkin (“cone.”)]
_Alnus_ (Alder) (Figs. 324–326). In the majority of species the ♂-and
♀-catkins are both developed in the year previous to their flowering,
and pass the winter naked and bloom before the leaves expand. ♂-flower:
4 stamens. ♀-flower: the 5-lobed cover-scales of the ♀-catkin are woody
and remain attached to the axis, so that the entire catkin when ripe
resembles a small cone (Fig. 324 _b_). Each cover-scale supports two
winged or wingless nuts. ~In the native species of Alder the buds are
stalked (Fig. 324 _k_). The bud-scales are formed by the stipules of
the lowest leaves.~
_Betula_ (Birch). The ♂-catkins, in the native species, appear
in autumn, the ♀-catkins in the flowering year on leaf-bearing,
short-lived shoots. ♂-flowers: 2 stamens, divided (Fig. 328 _A_). The
3-lobed cover-scales (Fig. 327 _a_) of the ♀-catkin are detached from
the axis; each cover-scale supports 3 broadly winged nuts (_b_).
~The stem has cork with annual rings. The young twigs and leaves have
aromatic resin glands.~
[Illustration: FIG. 325.--_Alnus glutinosa_: _A_ dichasium
of ♂-flowers seen from the front; _B_ the same from inside;
_C_ the same from the back; _D_ dichasium of ♀-flowers with
subtending-leaf and four bracteoles. The letters _b_, α, β, β′, β
are the same as in Fig. 326 _A_.]
[Illustration: FIG. 326.--_Alnus glutinosa_: diagram of dichasia
of ♂ (_A_) and ♀ (_C_) catkins; _B_ a cone-scale. All the
bracteoles in _A_ and _C_ are slightly pressed from their normal
position.]
THE INFLORESCENCES OF THE ALDER.--In the axil of each
cover-scale [_b_ in the Figs] is situated, in the ♂-catkins
(Figs. 326 _A_, 325 _A-C_) a 3-flowered dichasium, the
flowers of which have a 4-partite perianth, the posterior
perianth-segments being sometimes almost suppressed, and 4
stamens with undivided filaments. In the ♀-catkin (Figs. 325
_D_, 326 _C_) a 2-flowered dichasium is found, the middle
flower being suppressed (indicated by a star in _C_). In both
instances the inflorescences have two bracteoles (α-β) and the
flowers borne in their axils have each one bracteole (β′), the
other one (α′) being suppressed and therefore in 326 _A_ and _C_
only represented by a dotted line; these four bracteoles unite
with the cover-scale (_b_) which supports the entire dichasium,
to form the 5-lobed “cone-scale” (Fig. 326 _B_) which in the
♀-catkin eventually becomes woody.
THE INFLORESCENCES OF THE BIRCH.--A 3-flowered dichasium is
situated in the axil of the cover-scale in both ♂-and ♀-catkins
(Fig. 328 _A_, _B_); only the central flower has bracteoles
(α-β) (the lateral flowers having no bracteoles), and these
bracteoles unite, as in the Alder, with the supporting
cover-scale (_b_), and form a three-lobed cone-scale (Fig. 327
_a_).
While the ♀-flower exactly resembles that of the Alder, the
reduction of the ♂-flower, already described in the Alder, is
carried further, so that often only the 2 median perianth-leaves
are developed (Fig. 328 _A_); there are also _only_ 2 stamens,
these being deeply cleft, while the other 2 are suppressed.
About 50 species; N. Temp.--Fossil-forms certainly occur in
the Oligocene. During the Glacial period the Dwarf-birch (_B.
nana_) extended over Europe; at the present time it is confined
to the moors and mountains of N. Europe and N. America and Asia.
Wind-pollinated.
USES.--Important forest trees. The bark contains tannic acid.
The tar of the Birch is used in the preparation of Russia
leather; whilst its spring sap is very saccharine, and is used
in some places for making a fermented drink. Its external bark
is used for roofing, for baskets, etc.
[Illustration: FIG. 327.--_Betula verrucosa_: _a_ cone-scale; _b_
fruit.]
[Illustration: FIG. 328.--Diagrams of dichasia in the ♂-(_A_) and
♀-(_B_) catkins of Birch.]
Order 2. =Corylaceæ= (=Hazel-nuts=). Monœcious. The ♂-catkins are long
and cylindrical; the ♂-flowers are placed singly in the axil of the
subtending-leaf (cover-scale); they are _naked_ and formed of a number
of _divided_ stamens, which are partly united with the cover-scale,
4 in the Hazel, apparently 8 (Figs. 330 _A_, 329 _B_, _C_), more on
the Hornbeam. The ♀-flowers have a very small, _superior_ perianth;
in the axil of each cover-scale a 2-flowered dichasium (Fig. 329
_D_) is present, of which the central flower (* in Fig. 330 _B_)
is suppressed. The gynœceum is bicarpellary as in the Birches; the
ovary is bilocular, with two long styles (Fig. 329 _D-F_); the loculi
have 1 (-2) ovules (Fig. 330 _B_). Each single ♀-flower and fruit is
surrounded by a _leaf-like covering_, the _cupule_ (husk), which is
_formed of three floral-leaves_ (namely, the bract of a lateral flower,
and its own bracteoles; thus in Fig. 330 _B_, α, α′, β’ form the cupule
for the left-hand flower, and β, α_[1}, β_[1}, the cupule for the
right-hand).
_Corylus_ (Hazel-nut, Fig. 329). The long, cylindrical ♂-catkins pass
the winter naked, 2–3 together, on short branches. The very small
♀-catkins are enclosed in buds, in which they pass the winter; these
buds are situated in the axils of the fallen foliage-leaves, and it
is only by their larger size that they may be distinguished from the
ordinary foliage-buds. In spring the ♀-catkins are easily recognised
by their red, projecting stigmas (Fig. 329 _A_). The cupule--the
“husk”--is tubular, fringed, and envelopes the nut. ~The leaves are
alternate and unsymmetrical, the external side being larger than
the internal; this is connected with the vernation, the blade being
conduplicate in the bud; the stipules are deciduous. The bud-scales
are formed of stipules, the most internal having a leaf-blade attached
to them which is suppressed in the external ones. The cotyledons remain
underground on germination.~
[Illustration: FIG. 329.--_Corylus avellana_: _A_ branch at
the time of flowering with ♂-and ♀-catkins; _B_ ♂-flower with
subtending-leaf (bract) and two bracteoles; _C_ the same without
the anthers; _D_ view of interior of ♀-dichasium shortly after
fertilisation; _E_ young fruit with cupule; _F_ similar one with
the cupule opened; _G_ mature ♀-fruits; _H_ nut.]
_Carpinus_ (_C. betulus_, Hornbeam). The ♂-and ♀-catkins do not appear
till the leaves are shooting. The ♀-catkin in this instance is also
long and cylindrical. The cupule in _C. betulus_ is 3-lobed, and
to a slight extent only embraces the base of the ribbed nut (Fig.
331); each lobe corresponds to a floral-leaf. ~Whilst the carpels
are placed medianly in _Corylus_, in _Carpinus_, on the other hand,
they are situated transversely, as in the case of the _Betulaceæ_.
The lamina of the leaf is not conduplicate in the bud, but flat,
and folded only along the lateral veins, which are also indicated
in the form of the fully-developed leaf; otherwise the vegetative
characters are essentially the same as in the Hazel. The cotyledons
are aerial.--_Ostrya_ resembles the Hornbeam, but the cupule completely
envelopes the nut, as a sac open at the apex (Eur., N. Am., Japan).~
N. Am., Asia, and Europe; 25 species.--Fossil forms in the
Oligocene. Wind-pollinated. USES. As timber (_Carpinus betulus_)
and firewood. The fruits of _C. avellana_ (ordinary Hazel-nut),
_C. tubulosa_ (Lambert’s nut) and _C. colurna_ (Turkish Filbert)
are edible.
[Illustration: FIG. 330.--Diagrams of the ♂-flower (_A_) of
_Corylus_ and the dichasium of the ♀-flowers (_B_).]
[Illustration: FIG. 331.--Nut of the Hornbeam with cupule.]
Order 3. =Cupuliferæ.= Monœcious. The inflorescences make their
appearance with the leaves, arising in the axils of the leaves of
the same year. _A woody cupule_ furnished externally with scales or
spines is _common_, and surrounds 1-several flowers (the cupule in
the Corylaceæ never encloses more than a _single_ flower or fruit).
The ♂-flower has a united perianth, which is, however, 4–6 partite,
and encloses an indefinite number of undivided stamens. The ♀-flower
has a _superior, 6-merous_ perianth (3 + 3, compare Figs. 332 _D_,
334); the gynœceum is formed of 3 (or in _Castanea_ 4–6) carpels with
a corresponding number of stigmas (Figs. 332 _D_, _H_; 334, 335); and
the ovary has at the base 3 (-6) loculi (Fig. 333), each of which has 2
pendulous anatropous ovules; the fruit is a one-seeded nut (Figs. 332
_H_, 336).
The cupule of the Cupuliferæ, according to the opinion of Eichler, is
formed by united bracteoles, (compare Fig. 333, where the four valves
in the cupule of Castanea are considered as bracteoles of the lateral
flowers of the dichasium); according to another view (see Prantl, in
Engler’s _Bot. Jahrb._, viii., 1889), it is a ring-like axial outgrowth
independent of the bracteoles of the flower, whose scales and spines
are floral-leaves. The cupule in the Oak only encloses the base of the
fruit, but in the Eating-chestnut and Beech the fruit is completely
enclosed, and consequently the cupule must divide into a number of
valves (generally 4) to allow the fruit to escape. In the 3-flowered
dichasia of _Pasania_, Sect. Eupasania (Trop. Ind.), each individual
flower has its own cupule of the same structure and development as in
_Quercus_; and, moreover, each group of flowers has externally the
typical six bracteoles.
[Illustration: FIG. 332.--_Castanea vesca_: _A_ branch with
inflorescences; _B_ ♂-flower; _C_ young cupule with three
♀-flowers; _D_ ♀-flower; _E_ the same in longitudinal section;
_F_ cupule with 3 nuts (diminished); _G_, _H_ nuts (_G_ in
longitudinal section to show embryo).]
_Castanea_ (Eating-chestnut, Fig. 332). The catkins are erect (_A_),
cylindrical, with the ♀ at the base and the ♂ at the top, or some
are entirely ♂ and _composed of small dichasia_. The _cupule_ (_C_,
_F_) is 4-_valved_, provided with spines, and entirely envelops the 3
_nuts_; it is already developed at the time of flowering.--~♂-flowers
are most frequently borne in 7-flowered dichasia, and have a well
developed perianth, most frequently consisting of 6 leaves in two
whorls (Fig. 332 _B_), and a large number of stamens. ♀-flowers are
most frequently borne in 3-flowered dichasia (Figs. 332 _C_, 333); the
letters in Fig. 333 indicate the older theory, according to which the
4 bracteoles (α′-β′) of the two lateral flowers are thick and united
into a single 4-valved, _woody cupule_, which surrounds the 3 nuts,
and is furnished externally with spines; the spines are well developed
hair-structures.--6 carpels in two whorls.--The leaves in the vertical
shoots have a divergence of 2/5, 3/8, 5/13; on the horizontal shoots
they are alternate. The cotyledons remain underground on germination.~
[Illustration: FIG. 333.--Diagram of the cupule of _Castanea_.]
[Illustration: FIG. 334.--Female flower of _Fagus_ (mag.)]
_Fagus_ (Beech). The ♂-catkins are pendulous, capitate; the ♂-flowers
have an obliquely bell-shaped, fringed perianth, with 6–20 stamens.
♀-catkins erect, 2-flowered, borne singly in the axil of foliage-leaves
of the same year; the ♀-flower has a gynœceum formed of 3 carpels,
bearing an epigynous, 6-leaved perianth (Fig. 334). In this genus
_the dichasium has only 2 flowers_, the central one being suppressed.
_The cupule contains_, therefore, only 2 triangular nuts (“mast”).
~All the shoots have the leaves arranged in two rows; the rows are
on the underside, being only about 90° distant from each other; the
buds on the other hand approach each other towards the upper side. The
bud-scales are stipules without laminæ; in vernation the laminæ are
folded along the lateral ribs, the upper lateral portion being the
largest (as in Hornbeam and Chestnut). The cotyledons are folded, and
at germination are aerial, large, and reniform. 4 species (Europe,
Japan, N. Am.)--_Nothofagus_ (S. Am., New Zealand, S. Austr.)~
_Quercus_ (Oak, Fig. 335). Catkins simple. ♂-catkins long,
thin, _pendulous_, few-flowered. ♀-catkins erect; the cupule is
_cup-like_, _entire_, and encloses only the base of the solitary nut
(“acorn”).--~The ♂-flower has a similar construction to that of the
Chestnut. The ♀-catkin has not more than 5 flowers (single-flowered
dichasia, in which _only the central flower is developed_). The
scales on the cupules are no doubt leaf-structures in this case also.
According to another theory, the scales are hair-structures; they arise
on the internal face of the young cupule apparently in descending, but
really in ascending order. The rim of the cupule gradually expands.
In the ♀-flower (Fig. 335) the loculi of the gynœceum, together with
the ovules, are not developed until _after_ pollination.--The leaves
in all cases have a divergence of 2/5; the lowermost leaves on the
shoots are reduced to stipules which serve as the bud-scales (5 rows).
The laminæ are conduplicate, as in _Corylus_, and the external side is
the broadest. The cotyledons are fleshy and remain underground. 200
species.--_Pasania_ (100 species).~
[Illustration: FIG. 335.--_Quercus_: _A_ ♀-flower in its cupule
(mag.); _B_ longitudinal section through _A_, showing cupule,
perianth, and inferior ovary.]
[Illustration: FIG. 336.--Fruit of _Quercus_.]
368 species, in temperate climates, especially in Europe and
N. America. Authenticated forests have been found in the
Oligocene. The Beech has one species, _Fagus sylvatica_, in
Europe; it is a most important forest tree (in Denmark the most
important) and reaches its most northern limit near Alvesund
in Norway (60° N.L.), its northern boundary line passing
from Alvesund in a zig-zag line through Ludwigsort, south
of Königsberg, in Prussia, towards the Crimea. According to
Steenstrup and Vaupell, the Beech did not make its appearance
in Denmark until a comparatively recent time, the Oak then
being partially supplanted. Other species of Beech are found
in N. America and Japan. Several species of _Nothofagus_
occur in the South West of S. America, and in the colder
regions of the southern hemisphere. The Oaks grow especially
in temperate regions, _e.g._ in Western Asia, N. America,
and the mountains of Mexico. Evergreen species are found in
Tropical Asia, Himalaya, Japan and the Mediterranean region.
In this country there is one species of Oak (_Q. robur_), of
which there are three varieties (_Q. pedunculata, intermedia,
sessiliflora_). The Eating-chestnut is found in the South of
Europe, but is cultivated in the midland and southern counties
of England.--USES. The wood of these trees is very useful as
timber. The wood of _Q. tinctoria_ has a yellow colouring
matter (Quercitron-wood). The bark of the Oak contains a large
quantity of tannic acid, and is used for tanning; for this
purpose also the cupules of _Q. vallonea_, _ægilops_, _græca_,
and others from the Eastern Mediterranean, are used under the
name of “Valloons.” The Cork-oak (_Q. suber_; S.W. Europe) is
the most important tree from which cork is obtained, its bark
being very largely developed and stripped for cork. Gall-nuts
are found on many species; those of _Q. lusitanica_, var.
_infectoria_ (Eastern Mediterranean) are officinal, and likewise
the fruits (acorns) and the bark of _Quercus pedunculata_ and
_sessiliflora_. Oil is obtained from the Beech “mast.” The nuts
of the Chestnut tree are edible.