Bible Encyclopedias
Flower

FIG. 50

Obsolete calyx (c) of Madder (Rubia) adherent to the pistil, in the form of a rim.

FIG. 51. - Feathery pappus attached to the fruit of Groundsel (Senecio vulgaris). FIG. 52. - Caducous calyx (c) of Poppy. There are two sepals which fall off before the petals expand.

FIG. 53. - Fruit of Physalis Alkekengi, consisting of the persistent calyx (s), surrounding the berry (fr), derived from the ovary. (After Duchartre.) the calyx being trifid (three-cleft), quinquefid (five-cleft), &c., according to their number; or they reach to near the base in the form of partitions, the calyx being tripartite, quadripartite, quinquepartite, &c. The union of the parts may be complete, and the calyx may be quite entire or truncate, as in some Correas, the venation being the chief indication of the different parts. The cohesion is sometimes irregular, some parts uniting to a greater extent than others; thus a two-lipped or labiate calyx is formed. The upper lip is often composed of three parts, which are thus posterior or next the axis, while the lower has two, which are anterior. The part formed by the union of the sepals is called the tube of the calyx; the portion where the sepals are free is the limb. Occasionally, certain parts of the sepals undergo marked enlargement. In the violet the calycine segments are prolonged downwards beyond their insertions, and in the Indian cress (Tropaeolum) this prolongation is in the form of a spur (calcar), formed by three sepals; in Delphinium it is formed by one. In Pelargonium the spur from one of the sepals is adherent to the flower-stalk. In Potentilla and allied genera an epicalyx is formed by the development of stipules from the sepals, which form an apparent outer calyx, the parts of which alternate with the true sepals. In Malvaceae an epicalyx is formed by the bracteoles. Degenerations take place in the calyx, so that it becomes dry, scaly and glumaceous (like the glumes of grasses), as in the rushes (Juncaceae); hairy, as in Compositae; or a mere rim, as in some Umbelliferae and Acanthaceae, and in Madder (Rubia tinctorum, fig. 50), when it is called obsolete or marginate. In Compositae, Dipsacaceae and Valerianaceae the calyx is attached to the pistil, and its limb is developed in the form of hairs called pappus (fig. 51). This pappus is either simple (pilose) or feathery (plumose). In Valeriana the superior calyx is at first an obsolete rim, but as the fruit ripens it is shown to consist of hairs rolled inwards, which expand so as to waft the fruit. The calyx sometimes falls off before the flower expands, as in poppies, and is caducous (fig. 52); or along with the corolla, as in Ranunculus, and is deciduous; or it remains after flowering (persistent) as in Labiatae, Scrophulariaceae, and Boraginaceae; or its base only is persistent, as in Datura Stramonium. In Eschscholtzia and Eucalyptus the sepals remain united at the upper part, and become disarticulated at the base or middle, so as to come off in the form of a lid or funnel. Such a calyx is operculate or calyptrate. The existence or non-existence of an articulation determines the deciduous or persistent nature of the calyx.

The receptacle bearing the calyx is sometimes united to the pistil, and enlarges so as to form a part of the fruit, as in the apple, pear, &c. In these fruits the withered calyx is seen at the apex. Sometimes a persistent calyx increases much after flowering, and encloses the fruit without being incorporated with it, becoming accrescent, as in various species of Physalis (fig. 53); at other times it remains in a withered or marcescent form, as in Erica; sometimes it becomes inflated or vesicular, as in sea campion (Silene maritima). The corolla is the more or less coloured attractive inner floral envelope; generally the most conspicuous whorl. It is present in the greater number of Dicotyledons. Petals differ more from ordinary leaves than sepals do, and are much more nearly allied to the staminal whorl. In some cases, however, they are transformed into leaves, like the calyx, and occasionally leaf-buds are developed in their axil. They are seldom green, although occasionally that colour is met with, as in some species of Cobaea, Hoya viridiflora, Gonolobus viridiflorus and Pentatropis spiralis. As a rule they are highly coloured, the colouring matter being contained in the cell-sap, as in blue or red flowers, or in plastids (chromoplasts), as generally in yellow flowers, or in both forms, as in many orange-coloured or reddish flowers. The attractiveness of the petal is often due wholly or in part to surface markings; thus the cuticle of the petal of a pelargonium, when viewed with a z or 4-in. object-glass, shows beautiful hexagons, the boundaries of which are ornamented with several inflected loops in the sides of the cells.

Petals are generally glabrous or smooth; but, in some instances, hairs are produced on their surface. Petaline hairs, though sparse and scattered, present occasionally the same arrangement as those which occur on the leaves; thus, in Bombaceae they are stellate. Coloured hairs are seen on the petals of Menyanthes, and on the segments of the perianth of Iris. They serve various purposes in the economy of the flower, often closing the way to the honey-secreting part of the flower to small insects, whose visits would be useless for purposes of pollination. Although petals are usually very thin and delicate in their texture, they occasionally become thick and fleshy, as in Stapelia and Rafflesia; or dry, as in heaths; or hard and stiff, as in Xylopia. A petal often consists of two portions - the lower narrow, resembling the petiole of a leaf, and called the unguis or claw; the upper broader, like the blade of a leaf, and called the lamina or limb. These parts are seen in the petals of the wallflower (fig. 54). The claw is often wanting, as in the crowfoot (fig. 55) and the poppy, and the petals are then sessile. According to the development of veins and the growth of cellular tissue, petals present varieties similar to those of leaves. Thus the margin is either entire or divided into lobes or teeth. These teeth sometimes form a regular fringe round the margin, and the petal becomes fimbriated, as in the pink; or laciniated, as in Lychnis Flos-cuculi; or crested, as in Polygala. Sometimes the petal becomes pinnatifid, as in Schizopetalum. The median vein is occasionally prolonged beyond the summit of the petals in the form of a long process, as in Strophanthus hispidus, where it extends for 7 in.; or the prolonged extremity is folded downwards or inflexed, as in Umbelliferae, so that the apex approaches the base. The limb of the petal may be flat or concave, or hollowed like a boat. In Hellebore the petals become folded FIG. 56. FIG. 57. FIG. 58.

FIG. 54. - Unguiculate or clawed petal of Wallflower (Cheiranthus Cheiri). c, The claw or unguis; I, the blade or lamina.

FIG. 55. - Petal of Crowfoot (Ranunculus), without a claw, and thus resembling a sessile leaf. At the base of the petal a nectariferous scale is seen.

FIG. 56. - Tubular petal of Hellebore (Helleborus). FIG. 57. - Pansy (Viola tricolor). Longitudinal section of flower; v, bracteole on the peduncle; 1, sepals; ls, appendage of sepal; c, petals; cs, spur of the lower petals; fs, glandular appendage of the lower stamens; a, anthers. (After Sachs.) (From Vines' Students' Text-Book of Botany, by permission of Swan Sonnenschein & Co.) FIG. 58. - Part of the flower of Aconite (Aconitum Napellus), showing two irregular horn-like petals (p) supported on grooved stalks (o). These serve as nectaries. s, the whorl of stamens inserted on the thalamus and surrounding the pistil.

in a tubular form, resembling a horn (fig. 56); in aconite (fig. 58) some of the petals resemble a hollow-curved horn, supported on a grooved stalk; while in columbine, violet (fig. 57), snapdragon and Centranthus, one or all of them are prolonged in the form of a spur, and are calcarate. In Valeriana, Antirrhinum and Corydalis, the spur is very short, and the corolla or petal is said to be gibbous, or saccate, at the base. These spurs, tubes and sacs serve as receptacles for the secretion or containing of nectar.

A corolla is dipetalous, tripetalous, tetrapetalous or pentapetalous according as it has two, three, four or five separate petals. The general name of polypetalous is given to corollas having separate petals, while monopetalous, gamopetalous or sympetalous is applied to those in which the petals are united. This union generally takes place at the base, and extends more or less towards the apex; in Phyteuma the petals are united at their apices also. In some polypetalous corollas, as that of the vine, the petals are separate at the base and adhere by the apices. When the petals are equal as regards their development and size, the corolla is regular; when unequal, it is irregular. When a corolla is gamopetalous it usually happens that the lower portion forms a tube, while the upper parts are either free or partially united, so as to form a common limb, the point of union of the two portions being the throat, which often exhibits a distinct constriction or dilatation. The number of parts forming such a corolla can be determined by the divisions, whether existing as teeth, crenations, fissures or partitions, or if, as rarely happens, the corolla is entire, by the venation. The union may be equal among the parts, or some may unite more than others.

Amongst regular polypetalous corollas may be noticed the rosaceous corolla (fig. S9), in which there are five spreading petals, having no claws, and arranged as in the rose, strawberry and Potentilla; the caryophyllaceous corolla, in which there are five petals with long, narrow, tapering claws, as in many of the pink tribe; the cruciform, having four petals, often unguiculate, placed opposite in the form of a cross, as seen in wallflower, and in other plants called cruciferous. Of irregular polypetalous corollas the most marked is the papilionaceous (fig. 40), in which there are five petals: - one superior (posterior), st, placed next to the axis, usually larger than the rest, called the vexillum or standard; two lateral, a, the alae or wings; two inferior (anterior), partially or completely covered by the alae, and often united slightly by their lower margins, so as to form a single keel-like piece, car, called carin g , or keel, which embraces the essential organs. This form of corolla is characteristic of British leguminous plants.

Regular gamopetalous corollas are sometimes campanulate or bell-shaped, as in (Campanula) (fig. 60); infundibuliform or funnel-shaped, when the tube is like an inverted cone, and the limb becomes more expanded at the apex, as in tobacco; hypocrateriform or salver-shaped, when there is a straight tube surmounted by a flat spreading limb, as in primula (fig. 61); tubular, having a long cylindrical tube, appearing continuous with the limb, as in Spigelia and comfrey; rotate or wheel-shaped, when the tube is very short, and the limb flat and spreading, as in forget-me-not, Myosotis (when the divisions of the rotate corolla are very acute, as in Galium, it is sometimes called stellate or star-like); urceolate or urn-shaped, when there is scarcely any limb, and the tube is narrow at both ends, and expanded in the middle, as in bell-heath (Erica cinerea). Some of these forms may become irregular in consequence of certain parts being more developed than others. Thus, in Veronica, the rotate corolla has one division much smaller than the rest, and in foxglove (Digitalis) there is a slightly irregular companulate corolla. Of irregular gamopetalous corollas there may be mentioned the labiate or lipped (fig. 62), having two divisions of the limb in the form of lips (the upper one, u, composed usually of two united petals, and the lower, 1, of three), separated by a gap.

In such cases the tube varies in length, and the parts in their union follow the reverse order of what occurs in the calyx, where two sepals are united in the lower lip and three in the upper. When the upper lip of a labiate corolla is much arched, and the lips separated by a distinct gap, it is called ringent (fig. 62). The labiate corolla characterizes the natural order Labiatae. When the lower lip is pressed against the upper, so as to leave only a chink between them, the corolla is said to be personate, as in snapdragon, and some other Scrophulariaceae. In some corollas the two lips become hollowed out in a remarkable manner, as in calceolaria, assuming a slipper-like appearance, similar to what occurs in the labellum of some orchids, as Cypripedium. When a tubular corolla is split in such a way as to form a strap-like process on one side with several tooth-like projections at its apex, it becomes ligulate or strap-shaped (fig. 63). This corolla occurs in many composite plants, as in the florets of dandelion, daisy and chicory. The number of divisions at the apex indicates the number of united petals, some of which, however, may be FIG. 54.

FIG. 59. - Rosaceous corolla (c) of the Strawberry (Fragaria vesca), composed of five petals without claws.

From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.

FIG. 60. - Flower of Campanula medium; d, bract; v, bracteoles.

abortive. Occasionally some of the petals become more united than others, and then the corolla assumes a bilabiate or two-lipped form, as seen in the division of Compositae called Labiatiflorae.

Petals are sometimes suppressed, and sometimes the whole corolla is absent. In Amorpha and Afzelia the corolla is reduced to a single petal, and in some other Leguminous plants it is entirely wanting. In the natural order Ranunculaceae, some genera, such as Ranunculus, globe-flower and paeony, have both calyx and corolla, while others, such as clematis, anemone and Caltha, have only a coloured calyx. Flowers become double by the multiplication of the parts of the corolline whorl; this arises in general from a metamorphosis of the stamens.

Certain structures occur on the petals of some flowers, which received in former days the name of nectaries. The term nectary was very vaguely applied by Linnaeus to any part of the flower which presented an unusual aspect, as the crown (corona) of narcissus, the fringes of the Passion-flower, &c. If the name is retained it ought properly to include only those parts which secrete a honey-like substance, as the glandular depression at the base of the perianth of the fritillary, or on the petal of Ranunculus (fig. 55), or on the stamens of Rutaceae. The honey secreted by flowers attracts insects, which, by conveying the pollen to the stigma, effect fertilization. The horn-like nectaries under the galeate sepal of aconite (fig. 58) are modified petals, so also are the tubular nectaries of hel lebore (fig. 56). Other modifications of some part of the flower, especially of the corolla and stamens, are produced either by degeneration or outgrowth, or by chorisis, or deduplication. Of this nature are the scales on the petals in Lychnis, Silene and Cynoglossum, which are formed in the same way as the ligules of grasses. In other cases, as in Samolus, the scales are alternate with the petals, and may represent altered stamens. In Narcissus the appendages are united to form a crown, consisting of a membrane similar to that which unites the stamens in Pancratium. It is sometimes difficult to say whether these structures are to be referred to the corolline or to the staminal row.

Petals are attached to the axis usually by a narrow base. When this attachment takes place by an articulation, the petals fall off either immediately after expansion (caducous) or after fertilization (deciduous). A corolla which is continuous with the axis and not articulated to it, as in campanula and heaths, may be persistent, and remain in a withered or marcescent state while the fruit is ripening. A gamopetalous corolla falls off in one piece; but sometimes the base of the corolla remains persistent, as in Rhinanthus and Orobanche. The stamens and the pistil are sometimes spoken of as the essential organs of the flower, as the presence of both is required in order that perfect seed may be produced. As with few exceptions the stamen represents a leaf which has been specially developed to bear the pollen or microspores, it is spoken of in comparative morphology as a microsporophyll; similarly the carpels which make up the pistil are the megasporophylls (see Angiosperms). Hermaphrodite or bisexual flowers are those in which both these organs are found; unisexual or diclinous are those in which only one of these organs appears, - those bearing stamens only, being staminiferous or " male "; those having the pistil only, pistilliferous or " female." But even in plants with hermaphrodite flowers self-fertilization is often provided against by the structure of the parts or by the period of ripening of the organs. For instance, in Primula and Linum some flowers have long stamens and a pistil with a short style, the others having short stamens and a pistil with a long style. The former occur in the so-called thrum-eyed primroses (fig. 61), the latter in the " pin-eyed." Such plants are called dimorphic. Other plants are timorphic, as species of Lythrum, and proper fertilization is only effected by combination of parts of equal length. In some plants the stamens are perfected before the pistil; these are called proterandrous, as in Ranunculus repens, Silene maritima, Zea Mays. In other plants, but more rarely, the pistil is perfected before the stamens, as in Potentilla argentea, Plantago major, Coix Lachryma, and they are termed proterogynous. Plants in which proterandry or proterogyny occurs are called dichogamous. When in the same plant there are unisexual flowers, both male and female, the plant is said to be nionoecious, as in the hazel and castor-oil plant. When the male and female flowers of a species are found on separate plants, the term dioecious is applied, as in Mercurialis and hemp; and when a species has male, female and hermaphrodite flowers on the same or different plants, as in Parietaria, it is polygamous. The stamens arise from the thalamus or torus within the petals, with which they generally alternate, forming one or more whorls, which collectively constitute the androecium. Their normal position is below the pistil, and when they are so placed (fig.64, a) upon the thalamus they are hypogynous. Sometimes they become adherent to the petals, or are epipetalous, and the insertion of both is looked upon as similar, so that they are still hypogynous, provided they are independent of the calyx and the pistil. In other cases they are perigynous or epigynous (fig. 65). Numerous intermediate forms occur, especially amongst Saxifragaceae, where the parts are half superior or half inferior. Where the stamens become adherent to the pistil so as to form a column, the flowers are said to be gynandrous, as in Aristolochia (fig.

66). These arrangements of parts are of great importance in classification. The stamens vary in number from one to many hundreds. In acyclic flowers there is often a gradual transition from petals to stamens, as in the white water-lily (fig. 31). When flowers become double by cultivation, the stamens are converted into petals, as in the paeony, camellia, rose, &c. When there is only one whorl the stamens are usually equal in number to the sepals or petals, and are arranged opposite to the former, and alternate with the latter. The flower is then isostemonous. When the stamens are not equal in number to the sepals or petals, the flower is anisostemonous. When there is more than one whorl of stamens, then the parts of each successive whorl alternate with those of the whorl preceding it. The staminal row is more liable to multiplication of parts than the outer whorls. A flower with a single row of stamens is haplostemonous. If the stamens are double the sepals or petals as regards number, the flower is diplostemonous; if more than double, polystemonous. The additional rows of FIG. 61. FIG. 62. FIG. 63.

FIG. 61. - Flower of cowslip (Primula veris) cut vertically. s, Sepals joined to form a gamosepalous calyx; c, corolla consisting of tube and spreading limb; a, stamens springing from the mouth of the tube; p, pistil.

FIG. 62. - Irregular gamopetalous labiate corolla of the Dead-nettle (Lamium album). The upper lip u is composed of two petals united, the lower lip (1) of three. Between the two lips there is a gap. The throat is the part where the tube and the labiate limb join. From the arching of the upper lip this corolla is called ringent.

FIG. 63. - Irregular gamopetalous ligulate flower of Ragwort (Senecio). It is a tubular floret, split down on one side, with the united petals forming a straplike projection. The lines on the flat portion indicate the divisions of the five petals. From the tubular portion below, the bifid style projects slightly.

From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.

FIG. 64. - Flower of Paeonia peregrina,in longitudinal section. k, Sepal; c, petal; a, stamens; g, pistil. (2 nat. size.) stamens may be developed in the usual centripetal (acropetal) order, as in Rhamnaceae; or they may be interposed between the pre-existing ones or be placed outside them, i.e. develop centrifugally (basipetally), as in geranium and oxalis, when the flower is said to be obdiplostemonous . When the stamens are fewer than twenty they are said to be definite; when above twenty they are indefinite, and are represented by the symbol 00. The number of stamens is indicated by the Greek numerals prefixed to the term androus; thus a flower with one stamen is monandrous, with two, three, four, five, six or many stamens, di-, tri-, tetr-, pent-, hexor polyandrous, respectively.

The function of the stamen is the development and distribution of the pollen. The stamen usually consists of two parts, a contracted portion, often thread-like, termed the filament (fig. 25 f), and a broader portion, usually of two lobes, termed the anther (a), containing the powdery pollen (p), and supported upon the end of the filament. That portion of the filament in contact with the anther-lobes is termed the connective. If the FIG. 65. - Flower of Aralia in vertical section. c, Calyx; p, petal; e, stamen; s, stigmas. The calyx, petals and stamens spring from above the ovary (o) in which two chambers are shown each with a pendulous ovule; d, disc between the stamens and stigmas. From Strasburger's Lehrbuch mission of Gustav Fischer.

anther is absent the FIG. 66. - Flowers of Aristolochia Clem- atitis cut through longitudinally. I. Young stamen is abortive, flower in which the stigma (N) is receptive and cannot perform and the stamens (3) have not yet opened; its functions. The II. Older flower with the stamens (S) anther is developed o n the c orolla dried up.er(X2) dth e hairs before the filament, and when the latter is not produced, the anther is sessile, as in the mistletoe.

The filament is usually, as its name imports, filiform or threadlike, and cylindrical, or slightly tapering towards its summit. It is often, however, thickened, compressed and flattened in various ways, becoming petaloid in Canna, Marania, water-lily (fig. 32); subulate or slightly broadened at the base and drawn out into a point like an awl, as in Butomus umbellatus; or clavate, that is, narrow below and broad above, as in Thalictrum. In some instances, as in Tamarix gallica, Peganum Harmala, and Campanula, the base of the filament is much dilated, and ends suddenly in a narrow thread-like portion. In these cases the base may give off lateral stipulary processes, as in Allium and Alyssum calycinum. The filament varies much in length and in firmness. The length sometimes bears a relation to that of the pistil, and to the position of the flower, whether erect or drooping. The filament is usually of sufficient solidity to support the anther in an erect position; but sometimes, as in grasses, and other wind-pollinated flowers, it is very delicate and hair-like, so that the anther is pendulous (fig. 105). The filament is generally continuous from one end to the other, but in some cases it is bent or jointed, becoming geniculate; at other times, as in the pellitory, it is spiral. It is colourless, or of different colours. Thus in fuchsia and Poinciana, it is red; in Adamia and Tradescantia virginica, blue; in Oenothera and Ranunculus acris , yellow.

Hairs, scales, teeth or processes of different kinds are some times developed on the filament. In spiderwort (Tradescantia virginica) the hairs are beautifully coloured, moniliform or necklace-like, and afford good objects for studying rotation of the protoplasm. Filaments are usually articulated to the thalamus or torus, and the stamens fall off after fertilization: but in Campanula and some other plants they are continuous with the torus, and the stamens remain persistent, although in a withered state. Changes are produced in the whorl of stamens by cohesion of the filaments to a greater or less extent, while the anthers remain free; thus, all the filaments of the androecium may unite, forming a tube round the pistil, or a central bundle when the pistil is abortive, the stamens becoming monadelphous, as occurs in plants of the Mallow tribe; or they may be arranged in two bundles, the stamens being diadelphous, as in Polygala, Fumaria and Pea; in this case the bundles may be equal or unequal. It frequently happens, especially in Papilionaceous flowers, that out of ten stamens nine are united by their filaments, while one (the postericr one) is free (fig. 68). When there are three or more bundles the stamens are triadelphous, as in Hypericum aegyptiacum, or polyadelphous, as in Ricinus communis (castor-oil). In some cases, as in papilionaceous flowers, the stamens cohere, having been originally separate, but in most cases each bundle is produced by the branching of a single stamen. When there are three stamens in a bundle we may conceive the lateral ones as of a stipulary nature. In Lauraceae there are perfect stamens, each having at the base of the filament two abortive stamens or staminodes, which may be analogous to stipules. Filaments sometimes are adherent to the pistil, forming a column (gynostemium), as in Stylidium, Asclepiadaceae, Rafflesia, and Aristolochiaceae (fig. 66); the flowers are then termed gynandrous. FIG. 69. FIG. 70.

FIG. 68. - Stamens and pistil of Sweet Pea (Lathyrus). The stamens are diadelphous, nine of them being united by their filaments (f), while one of them (e) is free; st, stigma; c, calyx.

FIG. 69. - Portion of wall of anther of Wallflower (Cheiranthus). ce, Exothecium; cf, endothecium; highly magnified.

FIG. 70. - Quadrilocular or tetrathecal anther of the flowering Rush (Butomus umbellatus). The anther entire (a) with its filament; section of anther (b) showing the four loculi.

The anther consists of lobes containing the minute powdery pollen grains, which, when mature, are discharged by a fissure or opening of some sort. There is a double covering of the anther - the outer, or exothecium, resembles the epidermis,and often presents stomata and projections of different kinds (fig. 69); the inner, or endothecium, is formed by a layer or layers of cellular tissue (fig. 69, cf), the cells of which der Botanik, by per FIG. 67. - Spikelet of Reed (Phragmites communis) opened out. a, b, Barren glumes; c, fertile glumes, each enclosing one flower with its pale, d; the zigzag axis (rhachilla) bears long silky hairs.

have a spiral, annular, or reticulated thickening of the wall. The endothecium varies in thickness, generally becoming thinner towards the part where the anther opens, and there disappears entirely. The walls of the cells are frequently absorbed, so that when the anther attains maturity the fibres are alone left, and these by their elasticity assist in discharging the pollen. The anther is developed before the filament, and is always sessile in the first instance, and sometimes continues so. It appears at first as a simple cellular papilla of meristem, upon which an indication of two lobes soon appears. Upon these projections the rudiments of the pollen-sacs are then seen, usually four in number, two on each lobe. In each a differentiation takes place in the layers beneath the epidermis, by which an outer layer of small-celled tissue surrounds an inner portion of large cells. Those central cells are the mother-cells of the pollen, whilst the small-celled layer of tissue external to them becomes the endothecium, the exothecium being formed from the epidermal layer.

In the young state there are usually four pollen-sacs, two for each anther-lobe, and when these remain permanently complete it is a quadrilocular or tetrathecal anther (fig. 70). Sometimes, however, only two cavities remain in the anther, by union of the sacs in each lobe, in which case the anther is said to be bilocular or dithecal. Sometimes the anther has a single cavity, and becomes unilocular, or monothecal, or dimidiate, either by the disappearance of the partition between the two lobes, or by the abortion of one of its lobes, as in Styphelia laeta and Althaea officinalis (hollyhock). Occasionally there are numerous cavities in the anther, as in Viscum and Rafesia. The form of the anther-lobes varies. They are generally of a more or less oval or elliptical form, or they may be globular, as in Mercurialis annua; at other times linear or clavate, curved, flexuose, or sinuose, as in bryony and gourd. According to the amount of union of the lobes and the unequal development of different parts of their surface an infinite variety of forms is produced. That part of the anther to which the filament is attached is the back, the opposite being the face. The division between the lobes is marked on the face of the anther by a groove or furrow, and there is usually on the face a suture, indicating the line of dehiscence. The suture is often towards one side in consequence of the valves being unequal. The stamens may cohere by their anthers, and become syngenesious, as in composite flowers, and in lobelia, jasione, &c.

The anther-lobes are united to the connective, which is either continuous with the filament or articulated with it. When the filament is continuous with the connective, and is prolonged so that the anther-lobes appear to be united to it throughout their whole length, and lie in apposition to it and on both sides of it, the anther is said to be adnate or adherent; when the filament ends at the base of the anther, then the latter is innate or erect. In these cases the anther is to a greater or less degree fixed. When, however, the attachment is very narrow, and an articulation exists, the anthers are movable (versatile) and are easily turned by the wind, as in Tritonia, grasses (fig. 105), &c., where the filament is attached only to the middle of the connective. The connective may unite the antherlobes completely or only partially. It is sometimes very short and is reduced to a mere point, so that the lobes are separate or free. At other times it is prolonged upwards beyond the lobes, assuming various forms, as in Acalypha and oleander; or it is extended backwards and downwards, as in violet (fig. 71), forming a nectar-secreting spur. In Salvia officinalis the connective is attached to the filament in a horizontal manner, so as to separate the two anther-lobes (fig. 72), one only of which contains pollen, the other being imperfectly developed and sterile. The connective is joined to the filament by a movable joint forming a lever which plays an important part in the pollinationmechanism. In Stachys the connective is expanded laterally, so as to unite the bases of the anther-lobes and bring them into a horizontal line.

The opening or dehiscence of the anthers to discharge their contents takes place either by clefts, by valves, or by pores. When the anther-lobes are erect, the cleft is lengthwise along the line of the suture - longitudinal dehiscence (fig. 25). At other times the slit is horizontal, from the connective to the - side, as in Alchemilla arvensis (fig. 73) and in Lemna; the dehiscence is then transverse. When the anther lobes are rendered horizontal by the enlargement of the connective, then what is really longitudinal dehiscence may appear to be transverse. The cleft does not always proceed the whole length of the anther-lobe at once, but often for a time it extends only partially. In other instances the opening is confined to the base or apex, each loculament opening by a single pore, as in Pyrola, Tetratheca juncea, Rhododendron, Vaccinium and Solanum (fig. 74), where there are two, and Poranthera, where there are four; whilst in the mistletoe the anther has numerous pores for the discharge of the pollen. Another mode of dehiscence is the valvular, as in the barberry (fig. 75), where each lobe opens by a valve on the outer side of the suture, separately rolling up from base to apex; in some of the laurel tribe there are two such valves for each lobe, or four in all. In some Guttiferae, as Hebradendron cambogioides (the Ceylon gamboge plant), the anther opens by a lid separating from the apex (circumscissile dehiscence) .

The anthers dehisce at different periods during the process of flowering; sometimes in the bud, but more commonly when the pistil is fully developed and the flower is expanded. They either dehisce simultaneously or in succession. In the latter case individual stamens may move in succession towards the pistil and discharge their contents, as in Parnassia palustris, or the outer or the inner stamens may first dehisce, following thus a centripetal or centrifugal order. These variations are intimately connected with the arrangements for transference of pollen. The anthers are called introrse when they dehisce by the surface next to the centre of the flower; they are extrorse when they dehisce by the outer surface; when they dehisce by the sides, as in Iris and some grasses, they are laterally dehiscent. Sometimes, from their versatile nature, anthers originally introrse become extrorse, as in the Passionflower and Oxalis. The usual colour of anthers is yellow, but they present a great variety in this respect. They are red in the peach, dark purple in the poppy and tulip, orange in Eschscholtzia, &c. The colour and appearance of the anthers often change after they have discharged their functions.

Stamens occasionally become sterile by the degeneration or non-development of the anthers, when they are known as staminodia, or rudimentary stamens. In Scrophularia the fifth stamen appears in the form of a scale; and in many Pentstemons it is reduced to a filament with hairs or a shrivelled membrane at the apex. In other cases, as in double flowers, the stamens are converted into petals; this is also probably the case with such FIG. 71. FIG. 13. FIG. 74.

s FIG. 72. FIG. 75.

FIG. 71. - Two stamens of Pansy (Viola tricolor), with their two anther-lobes and the connectives (p) extending beyond them. One of the stamens has been deprived of its spur, the other shows its spur c. FIG. 72. - Anther of Salvia officinalis. lf, fertile lobe full of pollen; ls, barren lobe without pollen; e, connective; f, filament.

FIG. 73. - Stamen of Lady's Mantle (Alchemilla), with the anther opening transversely.

FIG.74. - Stamen of a species of Nightshade (Solanum), showing the divergence of the anther-lobes at the base, and the dehiscence by pores at the apex.

FIG. 75. - The stamen of the Barberry (Berberis vulgaris), showing one of the valves of the anther (v) curved upwards, bearing the pollen on its inner surface.

plants as Mesembryanthemum, where there is a multiplication of petals in several rows. Sometimes, as in Canna, one of the anther-lobes becomes abortive, and a petaloid appendage is produced. Stamens vary in length as regards the corolla. Some are enclosed within the tube of the flower, as in Cinchona (included); others are exserted, or extend beyond the flower, as in Littorella or Plantago. Sometimes the stamens in the early state of the flower project beyond the petals, and in the progress of growth become included, as in Geranium striatum. Stamens also vary in their relative lengths. When there is more than one row or whorl in a flower, those on the outside are sometimes longest, as in many Rosaceae; at other times those in the interior are longest, as in Luhea. When the stamens are in two rows, those opposite the petals are usually shorter than those which alternate with the petals. It sometimes happens that a single stamen is longer than all the rest. A definite relation, as regards I ?' number, sometimes exists between the long and the short stamens. Thus, in some flowers the stamens are didynamous, having only four out of five stamens developed, and the two corresponding to the upper part of the flower longer than the two lateral ones. This occurs in Labiatae and Scrophulariaceae (fig. 76). Again, in other cases there are six stamens, whereof four long ones are arranged in pairs opposite to each other, and alternate with two isolated short ones (fig. 77), giving rise to tetradynamous flowers, as in Cruciferae. Stamens, as regards their direction, may be erect, turned inwards, outwards, or to one side. In the last-mentioned case they are called declinate, as in amaryllis, horse-chestnut and fraxinella.

The pollen-grains or microspores contained in the anther consist of small cells, which are developed in the large thick-walled mother-cells formed in the interior of the pollen-sacs (microsporangia) of the young anther. These mother-cells are either separated from one another and float in the granular fluid which fills up the cavity of the pollen-sac, or are not so isolated. A division takes place, by which four cells are formed in each, the exact mode of division differing in dicotyledons and monocotyledons. These cells are the pollen-grains. They increase in size and acquire a cell-wall, which becomes differentiated into an outer cuticular layer, or extine, and an inner layer, or intine. Then the walls of the mother-cells are absorbed, and the pollengrains float freely in the fluid of the pollen-sacs, which gradually disappears, and the mature grains form a powdery mass within the anther. They then either remain united in fours, or multiples of four, as in some acacias, Periploca graeca and Inga anomala, or separate into individual grains, which by degrees become mature pollen. Occasionally the membrane of the mother-cell is not completely absorbed, and traces of it are detected in a viscid matter surrounding the pollen-grains, as in Onagraceae. In orchidaceous plants the pollen-grains are united into masses, or pollinia (fig. 78), by means of viscid matter. In orchids each of the pollen-masses has a prolongation or stalk (caudicle) which adheres to a prolongation at the base of the anther (rostellum) by means of a viscid gland (retinaculum) which is either naked or covered. The term clinandrium is sometimes applied to the part of the column in orchids where the stamens are situated. In some orchids, as Cypripedium, the pollen has its ordinary character of separate grains. The number of pollinia varies; thus, in Orchis there are usually two, in Cattleya four, and in Laelia eight. The two pollinia in Orchis Morio contain each about 200 secondary smaller masses. These small masses, when bruised, divide into grains which are united in fours. In Asclepiadaceae the pollinia are usually united in pairs (fig. 79), belonging to two contiguous anther-lobes - each pollen-mass having a FIG. 78. FIG. 79. FIG. 80.

FIG. 78. - Pollinia, or pollen-masses, with their retinacula (g) or viscid matter attaching them at the base. The pollen masses (p) are supported on stalks or caudicles (c). These masses are easily detached by the agency of insects. Much enlarged.

FIG. 79. - Pistil of Asclepias (a) with pollen-masses (p) adhering to the stigma (s). b, pollen-masses, removed from the stigma, united by a gland-like body. Enlarged.

FIG. 80. - Stamen of Asclepias, showing filament f, anther a, and appendages p. Enlarged.

caudicular appendage, ending in a common gland, by means of which they are attached to a process of the stigma. The pollinia are also provided with an appendicular staminal covering (fig. 80). The extine is a firm membrane, which defines the figure of the pollen-grain, and gives colour to it. It is either smooth, or covered with numerous projections (fig. 81), granules, points or crested reticulations. The colour is generally yellow, and the surface is often covered with a viscid or oily matter. The intine is uniform in different kinds of pollen, thin and transparent, and possesses great power of extension. In some aquatics, as Zostera, Zannichellia, Naias, &c., only one covering exists.

Pollen-grains vary from a o 0 - to o-y of an inch or less in diameter. Their forms are various. The most common form of grain is ellipsoidal, more or less narrow at the extremities, which are called its poles, in contradistinction to a line equidistant from the extremities, which is its equator. Pollen-grains are also spherical; cylindrical and curved, as in Tradescantia virginica; C From Vines' Students' Text-Book of Botany, by permission of Swan Sonnenschein & Co.

FIG. 82. - Germinating pollengrain of Epilobium (highly mag.) bearing a pollen-tube s; e, exine; intine; abc, the three spots where the exine is thicker in anticipation of the formation of the pollen-tube developed in this case at a.

polyhedral in Dipsacaceae and Compositae; nearly triangular in section in Proteaceae and Onagraceae (fig. 82). The surface of the pollen-grain is either uniform and homogeneous, or it is marked by folds formed by thinnings of the membrane. There are also rounded portions of the membrane or pores visible in the pollengrain; these vary in number from one to fifty, and through one FIG. 76. - Corolla of foxglove (Digitalis purpurea), cut in order to show the didynamous stamens (two long and two short) which are attached to it.

From Strasburger's Lehrbueh der Botanik, by permission of Gustav Fischer.

FIG. 77. - Tetradynamous stamens (four long and two short) of wallflower (Cheiranthus Cheiri). FIG. 81. - Pollen of Hollyhock (Althaea rosea), highly magnified.

FIG. 83. - Male flower of Pellitory (Parietaria officinalis), having four stamens with incurved elastic filaments, and an abortive pistil in the centre. When the perianth (p) expands, the filaments are thrown out with force as at a, so as to scatter the pollen.

or more of them the pollen-tube is extended in germination of the spore. In Monocotyledons, as in grasses, there is often only one, while in Dicotyledons they number from three upwards; when numerous, the pores are either scattered irregularly, or in a regular order, frequently forming a circle round the equatorial surface. Sometimes at the place where they exist, the outer membrane, in place of being thin and transparent, is separated in the form of a lid, thus becoming operculate, as in the passionflower and gourd. Within the pollen-grain is the granular protoplasm with some oily particles, and occasionally starch. Before leaving the pollen-sac a division takes place in the pollengrain into a vegetative cell or cells, from which the tube is developed, and a generative cell, which ultimately divides to form the male cells (see Angiosperms and Gymnosperms).

When the pollen-grains are ripe, the anther dehisces and the pollen is shed. In order that fertilization may be effected the pollen must be conveyed to the stigma of the pistil.

Polling- Thisrocess termed pollination (see Pollination. p p ()' is promoted in various ways, the whole form and structure of the flower having relation to the process. In some plants, as Kalmia and Pellitory (fig. 83), the mere elasticity of the filaments is sufficient to effect this; in other plants pollination is effected by the wind, as in most of our forest trees, grasses, &c., and in such cases enormous quantities of pollen are produced. These plants are anemophilous . But the common agents for pollination are insects. To allure and attract them to visit the flower the odoriferous secretions and gay colours are developed, and the position and complicated structure of the parts of the flower are adapted to the perfect performance of the process, It is comparatively rare in hermaphrodite flowers for self-fertilization to occur, and the various forms of dichogamy, dimorphism and trimorphism are fitted to prevent this.

Under the term disk is included every structure intervening between the stamens and the pistil. It was to such structures. that the name of nectary was applied by old authors.

It presents great varieties of form, such as a ring, scales, glands, hairs, petaloid appendages, &c., and in the progress of growth it often contains saccharine matter, thus becoming truly nectariferous. The disk is frequently formed by degeneration or transformation of the staminal row. It may consist of processes rising from the torus, alternating with the stamens, and thus representing an abortive whorl; or its parts may be opposite to the stamens. In some flowers, as Jatropha Curcas, in which the stamens are not developed, their place is occupied by glandular bodies forming the disk. In Gesneraceae and Cruciferae the disk consists of toothlike scales at the base of the stamens. The parts composing the disk sometimes unite and form a glandular ring, as in the orange; or they form a dark-red lamina covering the pistil, as in Paeonia Moutan (fig. 84); or a FIG. 84. - Flower of Tree waxy lining of the hollow receptacle, Paeony (Paeonia Moutan), as in the rose; or a swelling at the deprived of its corolla, and top of the ovary, as in Umbelliferae, showing the disk in the form in which the disk is said to be of a fleshy expansion (d) ep i gynous. The enlarged torus covering the ovary.

covering the ovary in Nymphaea (Castalia) and Nelumbium may be regarded as a form of disk.

The pistil or gynoecium occupies the centre or apex of the flower, and is surrounded by the stamens and floral envelopes when these are present. It constitutes the innermost whorl, which after flowering is changed into the fruit and contains the seeds. It consists essentially of two parts, a basal portion forming a chamber, the ovary, containing the ovules attached to a part called the placenta, and an upper receptive portion, the stigma, which is either seated on the ovary (sessile), as in the tulip and poppy, or is elevated on a stalk called the style, interposed between the ovary and stigma. The pistil consists of one or more modified leaves, the carpels (or megasporophylls). When a pistil consists of a single carpel it is simple or monocarpellary (fig. 85). When it is composed of several carpels, more or less united, it is compound or polycarpellary (fig. 86). In the first-mentioned case the terms carpel and pistil are synonymous. Each carpel has its own ovary, style (when present), and stigma, and may be regarded as formed by a folded leaf, the upper surface of which is turned inwards towards the axis, and the lower outwards, while from its margins are developed one or more ovules. This comparison is borne out by an examination of the flower of the double-flowering cherry. In it no fruit is produced, and the pistil consists merely of sessile leaves, the limb of each being green and folded, with a narrow prolongation upwards, as if from the midrib, and ending in a thickened portion. In Cycas the carpels are ordinary leaves, with ovules upon their margin.

A pistil is usually formed by more than one carpel. The carpels may be arranged either at the same or nearly the same height FIG. 85.

From Strasburger's Lenrbuch der Bolanik, by permission of Gustav Fischer.

S FIG. 86. FIG. 89. FIG. 88. FIG. 90.

FIG. 85. - Pistil of Broom (Cytisus) consisting of ovary o, style s, and stigma t. It is formed by a single carpel.

FIG. 86. - Vertical section of the flower of Black Hellebore (Helleborus niger). The pistil is apocarpous, consisting of several distinct carpels, each with ovary, style and stigma. The stamens are indefinite, and are inserted below the pistil (hypogynous).

FIG. 87. - Fruit of the Strawberry (Fragaria vesca), consisting of an enlarged succulent receptacle, bearing on its surface the small dry seed-like fruits (achenes).

FIG. 88. - Fruit of Rosa alba, consisting of the fleshy hollowed axis s', the persistent sepals s, and the carpels fr. The stamens (c) have withered. (After Duchartre.) FIG. 89. - Pistil of Ranunculus. x, Receptacle with the points of insertion of the stamens a, most of which have been removed.

FIG. 90. - Syncarpous Pistil of Flax (Linum), consisting of five carpels, united by their ovaries, while their styles and stigmas are separate.

in a verticil, or at different heights in a spiral cycle. When they remain separate and distinct, thus showing at once the composition of the pistil, as in Caltha, Ranunculus, hellebore (fig. 86), and Spiraea, the term apocarpous is applied. Thus, in Sedum (fig. 2 2) the pistil consists of five verticillate carpels o, alternating with the stamens e. In magnolia and Ranunculus (fig. 89) the separate carpels are numerous and are arranged in a spiral cycle upon an elongated axis or receptacle. In the raspberry the carpels are on a conical receptacle; in the strawberry, on a swollen succulent one (fig. 87); and in the rose (fig. 88), on a hollow one. When the carpels are united, as in the pear, arbutus and chickweed, the pistil becomes syncarpous. The number of carpels in a pistil is indicated by the Greek numeral. A flower with a simple pistil is monogynous; with two carpels, digynous; with three carpels, trigynous, &c.

The union in a syncarpous pistil is not always complete; it may take place by the ovaries alone, while the styles and stigmas remain free (fig. 90), and in this case, when the ovaries form apparently a single body, the organ receives the name of compound ovary; or the union may take place by the ovaries and styles, while the stigmas are disunited; or by the stigmas and the summit of the style only. Various intermediate states exist, such as partial union of the ovaries, as in the rue, where they coalesce at their base; and partial union of the styles, as in Malvaceae. The union is usually most complete at the base; but in Labiatae the styles are united throughout their length, and in Apocynaceae and Asclepiadaceae the stigmas only. When the union is incomplete, the number of the parts of a compound pistil may be determined by the number of styles and stigmas; when complete, the external venation, the grooves on the surface, and the internal divisions of the ovary indicate the number.

The ovules are attached to the placenta, which consists of a mass of cellular tissue, through which the nourishing vessels pass to the ovule. The placenta is usually formed on the edges of the carpellary leaf (fig. 91) - marginal. In many cases, however, the placentas are formations from the axis (axile), and are not connected with the carpellary leaves. In marginal placentation the part of the carpel bearing the placenta is the inner or ventral suture, corresponding to the margin of the folded carpellary leaf, while the outer or dorsal suture corresponds to the midrib of the carpellary leaf. As the placenta is formed on each margin of the carpel it is essentially double. This is seen in cases where the margins of the carpel do not unite, but remain separate, and consequently two placentas are formed in place of one. When the pistil is formed by one carpel the inner margins unite and form usually a common marginal placenta, which may extend FIG. 91. - Pistil of Pea along the whole margin of the ovary after fertilization of the as far as the base of the style (fig. 1 ovules, developing to form Y (g 9), the fruit. f, Funicle or or may be confined to the base or stalk of ovule (ov); pl, plaapex only. When the pistil consists centa; s,withered style and of several separate carpels, or is stigma; c, persistent calyx.

apocarpous, there are generally separ ate placentas at each of their margins. In a syncarpous pistil, on the other hand, the carpels are so united that the edges of each of the contiguous ones, by their union, form a septum or dissepiment, and the number of these septa consequently indicates the number of carpels in the compound pistil (fig. 92). When the FIG. 92. FIG. 93. FIG. 94.

FIG. 92. - Trilocular ovary of the Lily (Lilium), cut transversely. s, Septum; o, ovules, which form a double row in the inner angle of each chamber. Enlarged.

FIG. 93. - Diagrammatic section of a quinquelocular ovary, composed of five carpels, the edges of which are folded inwards, and meet in the centre forming the septa, s. The ovules (o) are attached to a central placenta, formed by the union of the five ventral sutures. Dorsal suture, 1. FIG. 94. - Diagrammatic section of a five-carpellary ovary, in which the edges of the carpels, bearing the placentas and ovules o, are not folded inwards. The placentas are parietal, and the ovules appear sessile on the walls of the ovary. The ovary is unilocular.

dissepi:ments extend to the centre or axis, the ovary is divided into cavities or cells, and it may be bilocular, trilocular (fig. 92), quadrilocular, quinquelocular, or multilocular, according as it is formed by two, three, four, five or many carpels, each carpel corresponding to a single cell. In these cases the marginal placentas meet in the axis, and unite so as to form a single central one (figs. 92, 93), and the ovules appear in the central angle of the loculi. When the carpels in a syncarpous pistil do not fold inwards so that the placentas appear as projections on the walls of the ovary, then the ovary is unilocular (fig. 95) and the placentas are parietal, as in Viola (fig. 96). In these instances the placentas may be formed at the margin of the united contiguous leaves, so as to appear single, or the margins may not be united, each developing a placenta. Frequently the margins of the carpels, which fold in to the centre, split there into two lamellae, each of which is curved outwards and projects into the FIG. 97. FIG. 98.

FIG. 95. - Diagrammatic section of a five-carpellary ovary, in which the septa (s) proceed inwards for a certain length, bearing the placentas and ovules (o). In this case the ovary is unilocular, and the placentas are parietal. Dorsal suture, 1. FIG. 96. - Pistil of Pansy (Viola tricolor), enlarged. I, Vertical; 2, horizontal section; c, calyx; d, wall of ovary; o, ovules; p, placenta; s, stigma.

FIG. 97. - Transverse section of the fruit of the Melon (Cucumis Melo), showing the placentas with the seeds attached to them. The three carpels forming the pepo are separated by partitions. From the centre, processes go to circumference, ending in curved placentas bearing the ovules.

FIG. 98. - Diagrammatic section of a compound unilocular ovary, in which there are no indications of partitions. The ovules (o) are attached to a free central placenta, which has no connexion with the walls of the ovary.

loculament, dilating at the end into a placenta. This is well seen in Cucurbitaceae (fig. 97), Pyrola, &c. The carpellary leaves. may fold inwards very slightly, or they may be applied in a valvate manner, merely touching at their margins, the placentas then being parietal (fig. 94), and appearing as lines or thickenings along the walls. Cases occur, however, in which the placentas are not connected with the walls of the ovary, and form what is called a free central placenta (fig. 98). This is seen in many of the Caryophyllaceae and Primulaceae (figs. 99,100). In Caryophyllaceae, however, while the placenta is free in the centre, there are often traces found at the base of the ovary of the remains of septa, as if rupture had taken place, and, in rare instances, ovules are found on the margins of the carpels. But in Primulaceae no vestiges of septa or marginal ovules can be perceived at any period of growth; the placenta is always free, and rises in the centre of the ovary. Free central placentation, there fore, has been accounted for in two ways: either by supposing that the placentas in the early state were formed on the margins of 2 FIG. 95.

I FIG. 99. FIG.

100.

FIG. 99. - Pistil of Cerastium hirsutum cut vertically. o, Ovary; p, free central placenta; g, ovules; s, styles.

FIG. too. - The same cut horizontally, and the halves separated so as to show the interior of the cavity of the ovary o, with the free central placenta p, covered with ovules g. carpellary leaves, and that in the progress of development these leaves separated from them, leaving the placentas and ovules free in the centre; or by supposing that the placentas are not marginal but axile formations, produced by an elongation of the axis, and the carpels verticillate leaves, united together around the axis. The first of these views applies to Caryophyllaceae, the second to Primulaceae.

Occasionally, divisions take place in ovaries which are not formed by the edges of contiguous carpels. These are called spurious dissepiments. They are often horizontal, as in Cathartocarpus Fistula, where they consist of transverse cellular prolongations from the walls of the ovary, only developed after fertilization, and therefore more properly noticed under fruit. At other times they are vertical, as in Datura, where the ovary, in place of being two-celled, becomes four-celled; in Cruciferae, where the prolongation of the placentas forms a vertical partition; in Astragalus and Thespesia, where the dorsal suture is folded inwards; and in Oxytropis, where the ventral suture is folded inwards.

The ovary is usually of a more or less spherical or curved form, sometimes smooth and uniform on its surface, at other times hairy and grooved. The grooves usually indicate the divisions between the carpels and correspond to the dissepiments. The dorsal suture may be marked by a slight projection or by a superficial groove. When the ovary is situated on the centre of the receptacle, free from the other whorls, so that its base is above the insertion of the stamens, it is termed superior, as in Lychnis, Primula (fig. 61) and Peony (fig. 64) (see also fig. 28). When the margin of the receptacle is prolonged upwards, carrying with it the floral envelopes and stamina' leaves, the basal portion of the ovary being formed by the receptacle, and the carpellary leaves alone closing in the apex, the ovary is inferior, as in pomegranate, aralia (fig. 65), gooseberry and fuchsia (see fig. 30). In some plants, as many Saxifragaceae, a there are intermediate forms, in which the term half-inferior is applied to the ovary, whilst the floral whorls are halfsuperior. The style proceeds from the summit of the carpel (fig.

102), and is traversed by a narrow canal, in which there are some loose projecting cells, a continuation of the placenta, constituting what is called conducting tissue, which ends in the stigma. This is particularly abundant when the pistil is ready for fertilization. In some cases, owing to more rapid growth of the dorsal side of the ovary, the style becomes lateral (fig. roi); this may so increase that the style appears to arise from near the base, as in the strawberry, or from the base, as in Chrysobalanus Icaco, when it is called basilar. In all these cases the style still indicates the organic apex of the ovary, although it may not be the apparent apex. When in a compound pistil the style of each carpel is thus displaced, it appears as if the ovary were depressed in the centre, and the style rising from the depression in the midst of the carpels seems to come from the torus. Such a style is gynobasic, and is well seen in Boraginaceae.

The form of the style is usually cylindrical, more or less filiform and simple; sometimes it is grooved on one side, at other times it is flat, thick, angular, compressed and even petaloid, as in Iris (fig. 103) and Canna. In Goodeniaceae it ends in a cup-like expansion, enclosing the stigma. It sometimes bears hairs, which aid in the application of the pollen to the stigma, and are called collecting hairs, as in Campanula, and also in Aster and other Compositae. These hairs, during the upward growth of the style, come into contact with the already ripened pollen, and carry it up along with them, ready to be applied by insects to the mature stigma of other flowers. In Vicia and Lobelia the hairs frequently form a tuft below the stigma. The styles of a syncarpous pistil are either separate or united; when separate, they alternate with the septa; when united completely, the style is said to be simple (fig. 102). The style of a single carpel, or of each carpel of a compound pistil, may also be divided. Each division of the tricarpellary ovary of Jatropha Curcas has a bifurcate or forked style, and the ovary of Emblica officinalis has three styles, each of which is twice forked. The length of the style is determined by the relation which should subsist between the position of the stigma and that of the anthers, so as to allow the proper application of the pollen. The style is deciduous or persists after fertilization.

The stigma is the termination of the conducting tissue of the style, and is usually in direct communication with the placenta. It consists of loose cellular tissue, and secretes a viscid matter which detains the pollen, and causes it to germinate. This secreting portion is, strictly speaking, the true stigma, but the name is generally applied to all the divisions of the style on which the stigmatic apparatus is situated. The stigma alternates with the dissepiments of a syncarpous pistil, or, in other words, corresponds with the back of the loculaments; but in some cases it would appear that half the stigma of one carpel unites with half that of the contiguous carpel, and thus the stigma is opposite the dissepiments, that is, alternates with the loculaments, as in the poppy.

The divisions of the stigma mark the number of carpels which compose the pistil. Thus in Campanula a five-cleft stigma indicates five carpels; in Bignoniaceae, Scrophulariaceae and Acanthaceae, the two-lobed or bilamellar stigma indicates a bilocular ovary. Sometimes, however, as in Gramineae, the stigma of a single carpel divides. Its position may be terminal or lateral. In Iris it is situated on a cleft on the back of the petaloid divisions of the style (fig. 103). Some stigmas, as those of Mimulus, present sensitive flattened laminae, which close when touched. The stigma presents various forms. It may be globular, as in Mirabilis Jalapa; orbicular, as in Arbutus Andrachne; umbrella-like, as in Sarracenia, where, however, the proper stigmatic surface is beneath the angles of the large expansion of the apex of the style; ovoid, as in fuchsia; hemispherical; polyhedral; radiating, as in the poppy (fig. 104), where the true stigmatic rays are attached to a sort of peltate or shield-like body, which may represent depressed or flattened styles; cucullate, i.e. covered by a hood, in calabar bean. The lobes of a stigma are flat and pointed as in Mimulus and Bignonia, fleshy and blunt, smooth or granular, or they are feathery, as in many grasses (fig. 105) and other windpollinated flowers. In Orchidaceae the stigma is situated on the anterior surface of the column beneath the anther. In Asclepiadaceae the stigmas are united to the face of the anthers, and along with them form a solid mass.

The ovule is attached to the placenta, and destined to become the seed. Ovules are most usually produced on the margins of FIG. IOI. FIG. 102.

FIG. 104. FIG. 103.

FIG. 101. - Carpel of Lady's-mantle (Alchemilla) with lateral style s; o, ovary, st, stigma. Enlarged.

FIG. 102. - Pistil of Primrose (Primula) composed of five carpels which are completely united; o, ovary; s, style; st, stigma. Enlarged.

FIG. 103. - Gynoecium of the Flowerde-Luce (Iris), consisting of an inferior ovary (o) and a style which divides into three petaloid segments (s), each bearing a stigma (st).

FIG. 104. - Capsuleof Poppy, opening by pores (p), under the radiating peltate stigma (s).

FIG. 105. - Flower of a grass with glumes removed, showing three stamens and two feathery styles. p, Pale; 1, lodicules. Enlarged.

the carpellary leaves, but are also formed over the whole surface of the leaf, as in Butomus. In other instances they rise The ovule. from the floral axis itself, either terminal, as in Poly gonaceae and Piperaceae, or lateral, as in Primulaceae and Compositae. The ovule is usually contained in an ovary, and all plants in which the ovule is so enclosed are termed angiospermous; but in Coniferae and Cycadaceae it has no proper ovarian covering, and is called naked, these orders being denominated gymnospermous. In Cycas the altered leaf, upon the margin of which the ovule is produced, and the peltate scales, from which they are pendulous in Zamia, are regarded by all botanists as carpellary leaves. As for the Coniferae great discussion has arisen regarding the morphology of parts in many genera. The carpellary leaves are sometimes united in such a way as to leave an opening at the apex of the pistil, so that the ovules are exposed, as in mignonette. In Leontice thalictroides (Blue Cohosh), species of Ophiopogon, Peliosanthes and Stateria, the ovary ruptures immediately after flowering, and the ovules are exposed; and in species of Cuphea the placenta ultimately bursts through the ovary and corolla, and becomes erect, bearing the exposed ovules. The ovule is attached to the placenta either directly, when it is sessile, or by means of a prolongation funicle (fig. I io, f). This cord sometimes becomes much elongated after fertilization. The part by which the ovule is attached to the placenta or cord is its base or hilum, the opposite extremity being its apex. The latter is frequently turned round in such a way as to approach the base. The ovule is sometimes embedded in the placenta, as in Hydnora. FIG. I 06. FIG. 107. FIG.7108. FIG. 109.

FIGS. 106 and mg. - Successive stages in the development of an ovule. n, Nucellus; i, inner; o, outer integument in section; m, micropyle.

FIG. 108. - Orthotropous ovule of Polygonum in section, showing the embryo-sac s, in the nucellus n, the different ovular coverings, the base of the nucellus or chalaza ch, and the apex of the ovule with its micropyle m. FIG. 1 09. - Vertical section of the ovule of the Austrian Pine (Pinus austriaca), showing the nucellus a, consisting of delicate cellular tissue containing deep in its substance an embryo-sac b. The micropyle m is very wide.

The ovule appears at first as a small cellular projection from the placenta. The cells multiply until they assume a more or less enlarged ovate form constituting what has been called the nucellus (fig. 106, n), or central cellular mass of the ovule. This nucellus may remain naked, and alone form the ovule, as in some orders of parasitic plants such as Balanophoraceae, Santalaceae, &c.; but in most plants it becomes surrounded by certain coverings or integuments during its development. These appear first in the form of cellular rings at the base of the nucellus, which gradually spread over its surface (figs. 106, 107). In some cases only one covering is formed, especially amongst gamopetalous dicotyledons, as in Compositae, Campanulaceae, also in walnut, &c. But usually besides the single covering another is developed subsequently (fig. 106, o), which gradually extends over that first formed, and ultimately covers it completely, except at the apex. There are thus two integuments to the nucellus, an outer and an inner. The integuments do not completely invest the apex of the nucellus, but an opening termed the micropyle is left. The micropyle indicates the organic apex of the ovule. A single cell of the nucellus enlarges greatly to form the embryo-sac or megaspore (fig. 108, s). This embryo-sac increases in size, gradually supplanting the cellular tissue of the nucellus until it is surrounded only by a thin layer of it; or it may actually extend at the apex beyond it, as in Phaseolus and Alsine media; or it may pass into the micropyle, as in Santalum. In Gymnosperms it usually remains deep in the nucellus and surrounded by a thick mass of cellular tissue (fig. 109). For an account of the further development of the megaspore, and the formation of the egg-cell, from which after fertilization is formed the embryo, see Gymnosperms and Angiosperms.

The point where the integuments are united to the base of the nucellus is called the chalaza (figs. II i, 112). This is often coloured, is of a denser texture than the surrounding tissue, and is traversed by fibrovascular bundles, which pass from the placenta to nourish the ovule.

When the ovule is so developed that the chalaza is at the hilum (next the placenta), and the micropyle is at the opposite extremity, there being a short funicle, the ovule is orthotropous. This form is well seen in Polygonaceae (fig. I12), Cistaceae, and most gymnosperms. In such an ovule a straight line drawn from the hilum to the micropyle passes along the axis of the ovule. Where, by more rapid growth on one side than on the other, the nucellus, together with the integuments, is curved upon itself, so that the micropyle approaches the hilum,and ultimately is placed close to it, while the chalaza is at the hilum, the ovule is campylotropous (fig. I Io). Curved ovules are found in Cruciferae, and Caryophyllaceae. The inverted or anatropous ovule (fig. I I 1) is the commonest form amongst angiosperms. In this ovule the apex with the micropyle is turned towards the point of attachment of the funicle to the placenta, the chalaza being situated at the opposite extremity; and the funicle, which runs along the side usually next the placenta, coalesces with the ovule and constitutes the raphe (r), which often forms a ridge. The anatropous ovule arises from the placenta as a straight or only slightly curved cellular process, and as it grows, gradually becomes inverted, curving from the point of origin of the integuments (cf. figs. 106, 107). As the first integument grows round it, the amount of inversion increases, and the funicle becomes adherent to the side of the nucellus. Then if a second integument be formed it covers all the free part of the ovule, but does not form on the side to which the raphe is adherent. These may be taken as the three types of ovule; but there are various intermediate forms, such as semi-anatropous and others.

The position of the ovule relative to the ovary varies. When there is a single ovule, with its axis vertical, it may be attached to the placenta at the base of the ovary (basal placenta), and is then erect, as in Polygonaceae and Compositae; or it may be inserted a little above the base, on a parietal placenta, with its apex upwards, and then is ascending, as in Parietaria. It may hang from an apicilar placenta at the summit of the ovary, its apex being directed downwards, and is inverted or pendulous, as in Hippuris vulgaris; or from a parietal placenta near the summit, and then is suspended, as in Daphne Mezereum, Polygalaceae and Euphorbiaceae. Sometimes a long funicle arises from a basal placenta, reaches the summit of the ovary, and there bending over suspends the ovule, as in Armeria (sea-pink); at other times the hilum appears to be in the middle, and the ovule becomes horizontal. When there are two ovules in the same cell, they may be either collateral, that is, placed side by eh 1 h FIG. I10. FIG. III.

FIG. I io. - Campylotropous ovule of wall-flower (Cheiranthus), showing the funicle f, which attaches the ovule to the placenta; p, the outer, s, the inner coat, n, the nucellus, ch, the chalaza. The ovule is curved upon itself, so that the micropyle is near the funicle.

FIG. I I I. - Anatropous ovule of Dandelion (Taraxacum), nucellus, which is inverted, so that the chalaza ch, is removed from the base or hilum h, while the micropyle f is near the base. The connexion between the base of the ovule and the base of the nucellus is kept up by means of the raphe r. side (fig. 92), or the one may be erect and the other inverted, as in some species of Spiraea and Aesculus; or they may be placed one above another, each directed similarly, as is the case in ovaries containing a moderate or definite number of ovules. Thus, in the ovary of Leguminous plants (fig. 91), the ovules, o, are attached to the extended marginal placenta, one above the other, forming usually two parallel rows corresponding to each margin of the carpel. When the ovules are definite (i.e. are uniform, and can be counted), it is usual to find their attachment so constant as to afford good characters for classification. When the ovules are very numerous (indefinite), while at the same time the placenta is not much developed, their position exhibits great variation, some being directed upwards, others downwards, others transversely; and their form is altered by pressure into various polyhedral shapes. In such cases it frequently happens that some of the ovules are arrested in their development and become abortive.

When the pistil has reached a certain stage in growth it becomes ready for fertilization. Pollination having been effected, and the pollen-grain having reached the stigma in angio sperms or the summit of the nucellus in mnos erms P gY P it is detained there, and the viscid secretion from the glands of the stigma in the former case, or from the nucellus in the latter, induce the protrusion of the intine as a pollen-tube through the pores of the grain. The pollen-tube or tubes pass down the canal (fig. 112), through the conducting tissue of the style when present, and reach the interior of the ovary in angiosperms, and then pass to the micropyle of the ovule, one pollen-tube going to each ovule. Sometimes the micropyle lies close to the base of the style, and then the pollentube enters it at once, but frequently it has to pass some distance into the ovary, being guided in its direction by various contrivances, as hairs, grooves, &c. In gymnosperms the pollen-grain resting on the apex of the nucellus sends out its pollen-tubes, which at once penetrate the nucellus (fig. 113). In angiosperms when the pollentube reaches the micropyle it passes down into the canal, and this portion of it increases considerably in size. Ultimately the apex of the tube comes in contact with the tip of the embryo-sac and perforates it. The male cells in the end of the pollen-tube are then transmitted to the embryo-sac and fertilization is effected. Consequent upon this, after a longer or shorter period, those changes commence in the embryo-sac which result in the formation of the embryo plant, the ovule also undergoing changes which convert it into the seed, and fit it for a protective covering, and a store of nutriment for the embryo. Nor are the effects of fertilization confined to the ovule; they extend to other parts of the plant. The ovary enlarges, and, with the seeds enclosed, constitutes the fruit, frequently incorporated with which are other parts of the flower, as receptacle, calyx, &c. In gymnosperms the pollen-tubes, having penetrated a certain distance down the tissue of the nucellus, are usually arrested in growth for a longer or shorter period, sometimes nearly a year. Fruit and seed are discussed in a separate article - FRUIT. (A. B. R.)