Part 55

Rheum (Rhubarb, Fig. 354 A) has a 6-leaved, petaloid perianth (Pn 3 + 3) and 9 stamens (A 3^2 + 3). The 3-winged nut is not enclosed by the perianth.

Rumex (Dock, Fig. 354 B) has 6 stamens (A 3^2 + 0); the perianth is 6-leaved (Pr 3 + 3), green or red, and the triangular nut is enveloped by the 3 interior perianth-leaves, which point upwards and continue to grow after flowering. These perianth-leaves often have warts on their outer surface. ~The following are monœcious: R. acetosa and R. acetosella.~

Polygonum (Knot-grass, Figs. 354 C, D; 355). The petaloid perianth is most frequently 5-merous (2/5 spiral); 5–8 stamens. The nut is triangular (Fig. 354 C, 355), or lenticular (Fig. 354 D). ~There are two whorls of stamens, the external with introrse, and the internal with extrorse anthers. The gynœceum is often bicarpellate (Fig. 354 D).~

The flowers may be considered as constructed upon the monocotyledonous type. Pterostegia has a perfectly monocotyledonous flower with 5 trimerous whorls. Rheum likewise, but here the external staminal whorl is doubled (Fig. 254 A). Oxyria has a dimerous Rheum-flower (4-leaved perianth, 6 stamens, 2 stigmas). Rumex has a Rheum-flower with the suppression of the internal whorl of stamens (Fig. 354 B); Emex is a dimerous Rumex. Polygonum, to which Coccoloba, Muehlenbeckia and others are related, differs from Rheum chiefly in having one of the leaves, which in the latter takes part in the formation of the perianth, developed in this case into a bracteole (so that the perianth is reduced to five members), and several or all the stamens in the inner whorl become suppressed.--The perianth in Coccoloba and Muehlenbeckia is more or less perigynous and becomes fleshy, enclosing the fruit. Muehlenbeckia platyclada has flat branches with rudimentary leaves; sometimes branches with normal, arrow-shaped leaves are found. Atraphaxis.

POLLINATION. Rumex is wind-pollinated, the stigmas are therefore large and brush-like (indicated in Fig. 354 B). Rheum and Polygonum are insect-pollinated and have therefore capitate stigmas, etc.; honey-glands are situated at the base of the stamens (d, in Fig. 354 C, and n in Fig. 356); a few small-flowered Polygonum species are self-pollinated; Buckwheat (P. fagopyrum) is dimorphic and has long-styled and short-styled flowers (Fig. 356). Pol. bistorta is protandrous and homostyled.

About 750 species, most of which are found in the temperate regions of the Northern Hemisphere, some reaching as far as the snow line or into the Arctic regions (Oxyria, Kœnigia). Trees and shrubs are found in the Tropics: Coccoloba, Triplaris. Rheum is Central Asiatic.--The thick rhizomes of R. officinale (Rhubarb) are officinal. The rhizomes of the ordinarily cultivated species, R. undulatum and rhaponticum, are used in veterinary medicine. The following are cultivated as culinary plants for the sake of their leaves:--Rumex acetosa (Sorrel), R. patientia, R. scutatus, and Rheum undulatum (petioles). Several species of Polygonum (P. hydropiper and others) have a sharp, pungent taste. “Buckwheat” is the mealy fruit of Polygonum fagopyrum (Central Asia) and is of value as a farinaceous food. P. cuspidatum (P. sieboldi, Japan) is an ornamental plant.--Calligonum in sandy and stony deserts.

Order 2. =Piperaceæ (Peppers).= Shrubs or herbs, often with nodose, jointed stem; leaves simple, entire, often with curved veins; stipules wanting (Peperomia) or intrapetiolar and cap-like, often enclosing the terminal buds (Piper). The flowers in the group Pipereæ (Piper, Fig. 357, and Peperomia) are borne in spikes with fleshy axes (club-like), seldom in racemes, the outer ones are crowded and are ☿ or unisexual, always small, naked and without bracteoles; ~generally stamens 3 + 3, and gynœceum 3, but the number of the stamens may be reduced by suppression to 2, and the carpels to 1~. The flowers are situated in the axils of the small, generally shield-like floral-leaves. The ovary is always unilocular and has one upright, orthotropous ovule. Fruit a berry or drupe. Both endosperm and perisperm are present, the latter being especially well developed (Fig. 359).

Piper; generally shrubs with scattered leaves, and terminal inflorescences which are crowded to one side by the development of the highest lateral bud, so that they are situated opposite the leaves (Fig. 357). Many species have stems with an abnormal anatomical structure.--Peperomia; chiefly succulent herbs, often epiphytes, with opposite or verticillate leaves having aqueous tissue on the upper side.

The group Saurureæ (considered by some as an order, and perhaps representing a more original type) has 3–4 carpels with many ovules. Lactoris stands the highest with regular 3-merous perianth, 3 + 3 stamens and 3 carpels, which are united at the base. Fruit a capsule with several seeds. (It has one species from the island of Juan Fernandez, and is also placed in an order of its own, Lactoridaceæ, allied to the Magnoliaceæ, through Drimys).--Saururus has naked flowers; most frequently 6 stamens, and 4 carpels, free or united at the base, each with 2-4 orthotropous ovules. Fruit, small berries.--Houttuynia; stamens situated a little upward on the ovaries; placentation parietal; capsule many-seeded.

About 1,000 species; entirely tropical, especially from South America and East India. They are found chiefly among the underwood in damp, shady places; some, which are fleshy (Peperomia), live as epiphytes on trees; a few climb by roots.--USES. Several Piperaceæ are used medicinally and for spices on account of their pungent properties and the essential oils found in nearly all parts of the plant. The following are officinal: “Black-pepper” (the unripe, dried fruits) and “White-pepper” (the seeds of the ripe fruits) of Piper nigrum (climbing shrub, East Indian); “Cubeb” berries of P. cubeba (climbing shrub, Java). “Long-pepper” is the unripe inflorescence of P. longum, East India. The leaves of P. angustifolia (Matico) are officinal. The leaves of the Betelpepper (East India) are used together with the nuts of the Areca-palm to form the well-known East Indian intoxicating compound “Betel.” A good many others are also used.

Order 3. =Chloranthaceæ.= (Chloranthus, Hedyosmum) have opposite leaves, with stipules more or less united at the base, and inferior “drupes.” Ovules pendulous. Only endosperm. About 33 species, Tropical.

Family 7. =Curvembryæ.=

The plants in this family have a curved ovule, and most frequently a kidney-shaped seed (generally provided with fine, cuticular, projecting warts, Fig. 362 B), with a curved, peripheral embryo enclosing the endosperm which is most frequently floury (Figs. 362 C, 365 H; for exceptions, see Fig. 366); the seeds in all cases are borne on a centrally-placed, and in most cases free, placenta (they are “basal” when there is only 1 ovule in the ovary, Fig. 364). The flower is regular, hypogynous or perigynous (Fig. 364) (only rarely epigynous) and usually 5-merous. The flower which is most complete has 5 whorls (S5, P5, A5+5, G2-3–5), as in some genera of the Caryophyllaceæ (Figs. 360, 361); but from this type it becomes reduced, the petals and stamens being suppressed, so that finally 5 perianth-leaves, 5 stamens (opposite the perianth-leaves), and 2 carpels (Fig. 361 F) only are present; for example, in certain genera of the Caryophyllaceæ, in the Chenopodiaceæ, Amarantaceæ, and others. When the number of stamens is increased to more than 5 in the whorl, it is always possible to show that some of the stamens have been divided. The number of the carpels and ovules also becomes reduced; in the highest there is a central placenta, not free in its early stages, with a large number of ovules; in those which are most reduced there is only a single ovule, which is placed centrally at the base of the ovary [Fig. 364]. Somewhat corresponding changes are found in the fruit, which is a many-seeded capsule in those which have many ovules, but a one-seeded nut where there is one ovule. In the most reduced forms the flowers are generally unisexual.--Similar features are also present in the vegetative parts. Almost all the species are herbaceous, the leaves are simple and most frequently without stipules. ~The structure of the stem, especially in Chenopodiaceæ, Amarantaceæ, Nyctaginiaceæ and others, often differs from that of the ordinary Dicotyledon. In the woody portion of the stem and root several rings are sometimes formed which resemble annual rings but which are formed by new cambium-rings arising outside the old ones which then cease to divide.~

Order 1. =Caryophyllaceæ.= Herbaceous plants, with round, nodose stem; leaves opposite, slightly amplexicaul, simple, with sessile, undivided, entire lamina; stipules nearly always absent; the inflorescences are dichasia passing over into unipared scorpioid cymes. The flowers are regular, ☿ or unisexual, hypogynous or perigynous, 5-(or 4-) merous with 2–3–4–5 carpels; calyx persistent; corolla polypetalous. The ovary is unilocular (or originally, and sometimes also in the later stages, plurilocular below, e.g. Viscaria), with free styles and 1–several curved ovules on a central, free placenta. The fruit is a nut or a capsule opening apically with long or short valves (teeth, Fig. 362), equal to or double the carpels. For the seeds refer to the family. ~In Dianthus the embryo is straight.~

The flowers which are most complete have Sn, Pn, An + n (obdiplostemonous), Gn where n = 5 (Figs. 360, 361 A) or 4 (Fig. 361 B); the carpels may be placed opposite to the sepals (Fig. 360) or opposite to the petals (Fig. 361 A, B). Without any change taking place in the position of the other whorls, the carpels are next found reduced to 2–3–4 (see the genera); their number may easily be recognised by that of the styles. This is the construction in the majority of the genera in the two first groups. Stellaria media differs considerably. It may have (a) the flower as described above, with G3; (b), the corolla only absent, or (c) only the petal-stamens (A5 + 0, Fig. 361 C), or (d) all these as well as some of the sepal-stamens. The same applies to Sagina, Alsine, Cerastium, and others, and, finally, a series of genera are formed, with certain conditions of reduction which have become constant, and by a gradual series of steps lead to the most reduced form, which has only 5 sepals and 5 (or even as far as only 1) sepal-stamens (Fig. 361 D, E, F).--The PETALS in the Alsineæ are often deeply bifid. The sepal-stamens are most frequently the longest, and bear nectaries at the base (Fig. 363 st). In the most complete forms the ovary has partition-walls in the lower portion (Fig. 360); these do not, however, reach to the top, and generally soon disappear. The ovules, when numerous, are situated on the placenta in as many double rows as there are carpels. In the number of ovules a reduction from many to 1 takes place (Fig. 361). A comparison proves that the “free, centrally placed” placenta is formed by the ventral portion of the carpels. The single basal ovule in Herniaria (Fig. 364), Scleranthus, and others, is also borne on the carpels.

The vegetative branching is characteristic. One of the leaves in a pair is formed before the other, and has a more vigorous axillary bud; these stronger leaves stand in a ¼-spiral, the fifth above the first one, and the branches are consequently arranged in the same manner. In the inflorescence, however, it is the upper or second bracteole (β) whose axillary bud (w in Fig. 361) is most advanced. The bud of the first bracteole (α) becomes sometimes entirely suppressed, or in some this bracteole itself is suppressed.

The most original type appears to be represented by the Alsineæ. From this form on one side the Sileneæ, adapted in a higher degree for insect-pollination, are developed, and on the other side the Paronychieæ, with various reductions.

=1.= ALSINEÆ, STITCHWORT GROUP. Sepals free, and connected with them stellately expanded, slightly unguiculate (white or inodorous) petals; these, however, often become suppressed (Fig. 363). The fruit is a capsule.

=a.= As many carpels as sepals (4 or 5). Cerastium (Chickweed). The petals are bifid. Capsule cylindrical, frequently curved at the top, and opening by 10 teeth (Fig. 362).--~Malachium differs only in the 5-toothed capsule with bifid teeth.~--Spergula (Spurry). The petals are not bifid, capsule 5-valved; seeds winged. The leaves are linear, and appear as if placed in large numbers in a whorl, a branch being situated in the axil of each with leaves placed very close together at its base; stipules membranous.--~Sagina has Sn, Pn, An + n, or An, Gn, where n = 4 or 5. The corolla is often wanting.~

=b.= 3 (rarely 2) carpels (Fig. 361 C). Stellaria (Stitchwort) has deeply cleft petals. The number of stamens varies (see above).--Arenaria has entire petals. ~(To this group belong Alsine, Moehringia, Halianthus, or Honckenya (Fig. 363), which differ from each other, especially in the form of the seed and number of the capsular valves.) Spergularia has membranous stipules, as in Spergula.--Holosteum.~

=2.= PARONYCHIEÆ (Figs. 361 D, E, F; 364). Small, greenish plants. The leaves, in the majority, are opposite, with membranous stipules. The flowers are most frequently arranged in small dichasia; they are small and insignificant, perigynous (Fig. 364) or hypogynous. The corolla is in most cases wanting, and when present is very small; in general the calyx-stamens are developed, but the corolla-stamens may be represented by small scales (Fig. 364). Ovary most frequently with 1 ovule. Fruit, a nut, rarely a capsule; it is enclosed by the strongly perigynous floral axis (torus).

Scleranthus (Knapwell) is perigynous with bell-shaped torus; no corolla; corolla-stamens are wanting or rudimentary; some calyx-stamens may also be absent.--Corrigiola (Fig. 361 D); Illecebrum; Paronychia (Fig. 361 E); Herniaria (Figs. 361 F, 364).

=3.= SILENEÆ, PINK OR CARNATION GROUP. This has a gamosepalous calyx and unguiculate, white or red, petals, with outgrowths (ligule, corona, paracorolla) at the throat of the corolla. These structures are not found in the other groups, and are merely outgrowths at the junction of the limb and claw. The corolla, stamens and ovary are frequently raised above the calyx, upon a lengthened internode (gynophore). The flower has S5, P5, A5 + 5; fruit a capsule with many seeds.

=a.= 5-(rarely 3–4) carpellate ovary.--Lychnis (Campion, Fig. 360). The corolla is longer than the calyx; corona present. The capsule is 10- or 5-toothed, completely 1-chambered or 5-chambered at the base,--the genus has been divided accordingly into several genera: Melandrium, Lychnis, Viscaria. ~Some species are unisexual by the abortion of stamens or carpels (L. vespertina, diurna).~ Agrostemma (A. githago, Corn-cockle, Fig. 361 A) has a long-toothed calyx, the teeth exceeding the corolla; corona absent; 5-toothed capsule.

=b.= Tricarpellate.--Silene (Catch-fly). Six-toothed capsule; corona present in the majority.--~Cucubalus has berry-like fruits which finally become dry but do not dehisce.~

=c.= Bicarpellate (2 styles, 4-toothed capsule).--Dianthus (Pink); at the base of the calyx 1–several pairs of floral-leaves are situated; corona absent. The straight embryo is a peculiar exception.--Gypsophila has a campanulate, open calyx, 5-nerved, membranous between the nerves; corona absent; the flowers are generally small and numerous, in a large, paniculate dichasia.--Saponaria (Soapwort) has corona.

POLLINATION. Alsineæ has ordinary nectaries at the base of the calyx-stamens (Fig. 336): they are frequently protandrous but may often, in the absence of cross-pollination (in the less conspicuous species) pollinate themselves. Their open flowers are accessible to many kinds of insects (particularly flies and bees). Gynodiœcious flowers are found in several species, and the ☿-flowers are then generally more conspicuous than the ♀-flowers. That the ♀-flowers have descended from ☿-flowers is seen by the large staminodes found in them (Fig. 363). Arenaria peploides is diœcious (Fig. 363). The Sileneæ are as a rule adapted for pollination by insects with long probosces--especially butterflies,--and they are frequently protandrous, so that at first the calyx-stamens open, later on the corolla-stamens, then the stigmas expand. The honey is secreted by a ring-like nectary round the base of the ovary or by nectaries at the base of the stamens. Some only blossom and emit scent at night or in the evening (Lychnis vespertina, Silene nutans, Saponaria officinalis) and, like other night-flowers, are of a white or pale colour.

DISTRIBUTION. 1,100 species, especially in temperate climates, fewer in the colder zone, less still in the Tropics. The Paronychieæ are especially found in dry, sandy fields.