Part 62

Fig. 432.--Capsule (nat. size).

Fig. 433.--Transverse and longitudinal section of seed: bl the cotyledons; k the plumule; R the radicle; fr the endosperm; sk the testa.]

Linum (Flax) has 5-merous flowers. ~The main axis terminates in a flower; and the succeeding branching is cymose, or unipared scorpioid branching by unilateral development, and the flowers in consequence of the vigorous sympodial development of the lateral axis (and also by the leaves being displaced and pushed aside), assume a position apparently lateral (i.e. racemose) without bracts; each branch of the sympodium generally has 2 leaves. The testa is shining and smooth when dry, but its external cellular layer becomes mucilaginous in water.~--Radiola has a 4-merous flower. It is a small herb with opposite leaves, and regular, dichasial branching.

The anthers and stigmas in L. catharticum and usitatissimum develop simultaneously, and cross-pollination as well as self-pollination takes place. L. grandiflorum, perenne, and others, are dimorphic (short-and long-styled). There are 5 nectaries outside the stamens.

130 species; Linum and Radiola are native genera.--L. usitatissimum is extensively cultivated in Europe (especially in Russia and Belgium), N. America and elsewhere (its home no doubt being Asia), partly on account of the oil (linseed oil) which is extracted from the seeds, and partly on account of the bast of the stem, which has very thick-walled cells. The seeds and oil are OFFICINAL. The species cultivated in ancient times was L. angustifolium. Several species are cultivated as ornamental plants.

Order 3. =Geraniaceæ.= The majority are herbs with dichasial branching, and scattered or opposite, stalked, palminerved (rarely penninerved) leaves with small stipules. The flowers are regular (except Pelargonium) and 5-merous, with 10 or 5 stamens, which are slightly united at the base. Nectaries alternate with the corolla-stamens. The ovary is most frequently 5-locular, deeply 5-grooved, and bears 1 well developed style (“beak”), which towards the apex divides into 5 branches bearing stigmas; ovules 1 in each loculus, pendulous or ascending. The 5 carpels become detached from one another when ripe, and bend or roll back (Fig. 434) or become spirally twisted in the upper “beak-like” part (Figs. 435, 436), whilst a central column (septal column) persists; each carpel, in consequence, remains either closed, and the fruit is a 5-merous schizocarp whose nut-like lower portion, containing the seed, is forced into the ground, thus burying the seed by the movements of the spirally-twisted, hygroscopic “beak” (Figs. 435, 436); or it opens along the ventral suture, so that the seeds may fall out, and it is then a 5-valved capsule, with septicidal dehiscence (Fig. 434) and the rolling up often takes place so suddenly and violently that the seeds are shot out to considerable distances. The embryo is usually green and curved, and the cotyledons are folded; endosperm is wanting.

Geranium (Crane’s-bill) has 5 + 5 stamens,and a septicidal capsule; the carpels most frequently remain suspended from the apex of the column (Fig. 434). The leaves are most frequently palminerved. The flowers are situated solitarily or 2 together (2-flowered scorpioid cyme).--Erodium (Stork’s-bill); inflorescence a many-flowered unipared scorpioid cyme, stamens 5 + 0 (petal-stamens are wanting), and fruit a schizocarp whose carpels become detached; their beaks are hairy on the internal surface and twist themselves spirally (Fig. 436). The umbellate inflorescences are composed of multiflowered scorpioid cymes. The leaves are often penninerved.--~The most primitive type is represented by Biebersteinia: S5, P5, A5 + 5, G5 (ovaries free, and styles united above); fruit 5 small nuts. The most advanced type is Pelargonium, which has zygomorphic flowers, the posterior sepal being prolonged into a spur which becomes adnate to the peduncle; the petals are unequal in size; some of the petal-stamens are often wanting. (Erodium may be slightly zygomorphic).~

POLLINATION. The large-flowered Geranium-species are protandrous, e.g. G. pratense (one whorl of stamens opens first, and then the other, and succeeding these the stigmas, after shedding the pollen the stamens bend outwards); the small-flowered are also adapted, with various modifications, for self-pollination.--470 species; moderately hot climates, especially S. Africa.--Several Pelargonium-species, with numerous varieties, are ornamental plants (from S. Africa).

Order 4. =Tropæolaceæ.= Herbaceous, juicy plants which have scattered, long-stalked, peltate leaves without stipules, and often climb by their sensitive petioles. The flowers are situated singly in the axils of the foliage-leaves on long stalks, and are zygomorphic, the receptacle under the posterior sepal being prolonged into a spur; there are also differences between the posterior and anterior petals, the 2 posterior petals situated on the border of the spur being perigynous, and the edge of the anterior petals adjoining the claw fringed. After the 5 sepals (which are more or less coloured) and the 5 petals, follow 8 stamens (as the 2 median ones are suppressed, one from each whorl) and a gynœceum formed of 3 carpels; in each of the 3 loculi of the 3-grooved ovary is 1 ovule. The fruit is a schizocarp and divides into 3 1-seeded, drupe-like fruitlets, which do not (as in the Geraniaceæ) leave any pronounced column between them. Endosperm is wanting. The cotyledons are thick and sometimes slightly coalescent. ~Tubers often occur.~

Tropæolum.--About 40 species; all from America.

POLLINATION.--The spur is the receptacle for the nectar; the flowers are protandrous; the anthers open first, and one by one take up a position in front of the entrance to the spur, resuming their original position when the pollen is shed; the stigma finally takes their place after the filaments have bent backwards.--These plants have an acrid taste (hence the name “Nasturtium,” “Indian Cress”), on which account the flower-buds and young fruits of T. majus are used as capers. Some species are ornamental plants.

Order 5. =Balsaminaceæ.= Herbaceous, chiefly annual plants with juicy, brittle stems, so transparent that the vascular bundles may be distinctly seen. The leaves are simple, usually scattered, penninerved and dentate; stipules are wanting, but sometimes large glands are present in their place at the base of the petioles. The flowers are strongly zygomorphic; of their five 5-merous whorls the petal-stamens are suppressed (S5, P5, A5 + 0, G5); the sepals are coloured, the 2 anterior ones (Fig. 438 3, 5) are very small or entirely suppressed, the posterior one is very large and elongated into a spur, and the 2 lateral ones pushed forward; sometimes the weight of the spur turns the flower completely round, so that the posterior leaves assume an anterior position; apparently only 3 petals, since the lateral and the posterior petals become united in pairs, and the anterior is larger and differently shaped; the 5 stamens have very short and thick filaments united at the base, and their anthers finally adhere together and remain in this condition, covering over the gynœceum; the filaments ultimately rupture at the base, and the entire anthers are raised on the apex of the gynœceum as it grows up. The gynœceum has a sessile stigma and a 5-locular ovary. The fruit is a capsule which, on maturity, opens suddenly when irritated, dividing into valves from the base upwards, and as the 5 valves roll up elastically, the seeds are shot out on all sides to considerable distances; a central column persists (Fig. 439). The embryo is straight, and without endosperm.

Impatiens; in Europe only I. noli-me-tangere. 225 species; especially from Asia. Several species have two kinds of flowers: small, cleistogamic, but fertile; and large, coloured flowers, which in I. balsamine (ornamental plant, E. Ind.) are protandrous and pollinated by hive-and humble-bees, as they suck the honey from the spur.

Order 6. =Limnanthaceæ.= The flowers are regular and differ from all the other orders in the family by having the carpels not in front of the petals, but in front of the sepals (which are valvate), and further, the loculi are nearly free individually, but with a common gynobasic style; the ovules are ascending and apotropous (anatropous with ventral raphe). The fruit is a schizocarp, with nut-like cocci.--Limnanthes (4 species; N. Am.) perhaps belongs to another family.

Order 7. =Humiriaceæ.= Trees and shrubs; about 20 species; Trop. Am.

Family 13. =Columniferæ.=

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.

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).

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.

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.

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.