Part 31

_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.~

_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.~

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.

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.~

_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.

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.

_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.~

_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).~

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.

Family 4. =Juglandifloræ.=

This family resembles the Quercifloræ in the catkin-like inflorescences, the imperfect, _unisexual_ flowers, the epigynous perianth and the woody shoots with scattered leaves, etc., though it is in other respects very dissimilar; one point of difference is the presence of _aromatic_ compounds, but a more important divergence is found in the structure of the gynœceum, which is formed of two carpels with _one loculus_ and has one _basal_, _orthotropous and erect_ ovule, which, as in the Quercifloræ, does not become developed until after pollination; the fruit too is very different, being generally a _drupe_. _Endosperm absent._

Order 1. =Juglandaceæ (Walnuts).= Leaves _scattered_, _imparipinnate_, rich in _aromatic_ compounds. _Stipules absent._ Flowers unisexual. _Monœcious._ The ♂-catkins are lateral, generally on naked branches of the previous year, cylindrical, pendulous, many-flowered; the two bracteoles and the 2–4-leaved perianth of the ♂-flower unite with the subtending bract; the ♂-flower has indefinite stamens (6–20 in _Juglans_, Fig. 337 _A-D_). The ♀-catkins are terminal, generally on branches of the same year, few-flowered (Fig. 337 _F_); the ♀-flowers have a _superior_, 4-leaved perianth, a bicarpellate gynœceum, two styles with stigmas on the internal surface. The ovary, bracteoles and bract all unite together (Fig. 337 _E_). The fruit is generally a green or black _drupe_,[34] whose flesh (outer soft portion) in _Carya_ and _Juglans_ ruptures more or less irregularly, and frees the stone (“Walnut”).--~The stone in _Juglans_ is divided internally by one true (Fig. 337 _H_) and by several false, low partition walls into several _incomplete_ compartments, so that the two large _cotyledons_ become lobed and incised to fit like a cast into the irregularities of the inner surface of the stone; the embryo is exendospermous and covered with a thin testa.--THE LEAF SCARS are large and cordate with 3 groups of vascular bundles. The PITH in _Juglans_ and _Pterocarya_ is divided into chambers. The stone ruptures, on germination, along the dorsal suture into 2 valves; the cotyledons remain underground. In _Juglans regia_ a long row of accessory buds is found on the lowest internode (epicotyl) above the axils of the cotyledons. _Pollination by the wind._ Both protogynous and protandrous examples of _Juglans regia_ occur.--33 species, mostly in temperate North America.--USES. Walnuts are obtained from _J. nigra_ and _regia_; Hickory from North American species of _Carya_. The oil-containing seeds of several species are edible. _Pterocarya_ and others are cultivated as ornamental plants.~

Order 2. =Myricaceæ=. To this order belong shrubs or trees which have penninerved, simple, at most lobed or pinnatifid leaves, with or without stipules, and with yellow, aromatic, resin glands (Fig. 338 _a_). The flowers, situated in catkin-like spikes, are unisexual and _naked_, and supported by scale-like floral-leaves. ♂-flower: 4–6 (–16) stamens with short filaments; ♀: generally situated singly. The gynœceum has a short style with 2 long stigmas, and unites with the bracteoles, which form wing-like outgrowths on the ripe drupe as in _Pterocarya_ in the Juglandaceæ (Fig. 338). Cotyledons fleshy (Fig. 338 _b_).--_Myrica_; _Comptonia_.

40 species; Temperate.--_Myrica gale_ (Sweet-gale, Bog-myrtle) has been used in the preparation of beer (Sweet-willow beer) on account of its resinous essential oil. _M. cerifera_ (N. America) and species from the Cape, _M. quercifolia_ and others, form wax on the fruit which is used in the preparation of candles.

Family 5. =Urticifloræ.=

The flowers are regular, _hypogynous_, nearly always unisexual, _small_ and insignificant, with _single_, green perianth of 4–5 leaves. Stamens 4–5, _placed opposite_ the leaves of the perianth. Ovary formed of 1 or 2 carpels, most frequently _unilocular_, with one ovule (Fig. 340). The fruit is a _nut_, more rarely a drupe, with one seed, _generally endospermous_. ~The Nettles are the sole order in the family which has only one carpel (1 stigma); this turns the posterior side to the front (Fig. 340). The others have two carpels (2 stigmas) but the anterior only is fertile (Fig. 346) except in a few Ulmaceæ and Moraceæ.~