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FLOWER (Lat. flos, floris; Fr. fleur)

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Originally appearing in Volume V10, Page 558 of the 1911 Encyclopedia Britannica.
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FLOWER (Lat. flos, floris; Fr. fleur), a term popularly used for the bloom or blossom of a plant, and so by analogy for the fairest, choicest or finest part or aspect )f anything, and in various technical senses. Here we shall deal only with its botanical interest. It is impossible to give a rigid botanical definition of the term " flower." The flower is a characteristic feature of the highest group of the plant kingdom—the flowering plants (Phanerogams)—and is the name given to the association of organs, more or less leaf-like in form, which are concerned with the production of the fruit or seed. In modern ootanical works the group is often known as the seed-plants (Spermatophyta). As the seed develops from the ovule which has been fertilized by the pollen, the essential structures for seed-production are two, viz. the pollen-bearer or stamen and the ovule-bearer or carpel. These are with few exceptions foliar structures, known in comparative morphology as sporophylls, because they bear the spores, namely, the microspores or pollen-grains which are developed in the microsporangia or pollen-sacs, and the mega-spore, which is contained in the ovule or megasporangium. In Gymnosperms (q.v.), which represent the more primitive simple or branched, arises, while the leaves which arise on the axis between the bract and the outer envelope of the flower are bracteoles or bractlets. Bracts sometimes do not differ from the ordinary leaves, as in Veronica hederifolia, Vinca, Anagallis and Ajuga. In general as regards their form and appearance they differ from ordinary leaves, the difference being greater in the upper than in the lower branches of an inflorescence. They are distinguished by their position at the base of the flower or flower-stalk. Their arrangement is similar to that of the leaves. When the flower is sessile the bracts are often applied closely to the calyx, and may thus be confounded with it, as in the order Malvaceae and species of Dianthus and winter aconite (Eranthis), where they have received the name of epicalyx or calyculus. In some Rosaceous plants an epicalyx is present, due to the formation of stipulary structures by the sepals. In many cases bracts act as protective organs, within or beneath which the young flowers are concealed in their earliest stage of growth. When bracts become coloured, as in Amherstia nobilis, Euphorbia splendens, Erica elegans and Salvia splendens, they may be mistaken for parts of the corolla. They are sometimes mere scales or threads, and at other times are undeveloped, giving rise to the ebracteate inflorescence of Cruciferae and some Boraginaceae. Sometimes they are empty, no flower-buds being produced in their axil. A series of empty coloured bracts terminates the inflorescence of Salvia Horminum. The smaller bracts or bracteoles, which occur among the subdivisions of a branching inflorescence, often produce no, flower-buds, and thus anomalies occur in the floral arrangements. Bracts are occasion-ally persistent, remaining long attached to the base of the peduncles, but more usually they are deciduous, falling off earlyby an articulation. In some instances they form part of the fruit, becoming incorporated with other organs. Thus, the cones of firs and the stroboli of the hop are composed of a series of spirally arranged bracts covering fertile flowers; and the scales on the fruit of th pine-apple are of the same nature. At the base of the general umbel in umbelliferous plants a whorl of bracts often exists, called a general involucre, and at the base of the smaller umbels or umbellules there is a similar leafy whorl called an involucel or partial involucre. In some instances, as in fool's-parsley, there is no general involucre, but simply an involucel; while in other cases, as in fennel or dill (fig. Is), neither involucre nor involucel is developed. In Compositae the name involucre is applied to the bracts surrounding the head of flowers (fig. 2, i), as in marigold, dandelion, daisy, artichoke. This involucre is frequently composed of several rows of leaflets, which are either of the same or of different forms and lengths, and often lie over each other in an imbricated manner. The leaves of the involucre are spiny in thistles and in teazel (Dipsacus), and hooked in burdock. Such whorled or verticillate bracts generally remain separate (polyphyllous), but may be united by cohesion (gamopkyllous), as in many species of Bupleurum and in Lavatera. In Compositae besides the involucre there are frequently chaffy and setose bracts at the base of each flower, and in Dipsacaceae a membranous tube surrounds each flower. These structures are-of the nature of an epicalyx. In the acorn the cupule or cup (fig. 3) is formed by a growing upwards of the flower-stalk immediately beneath the flower, upon which scaly or spiny protuberances appear; it is of the nature of bracts. Bracts also compose the husky covering of the hazel-nut. - When bracts become united, and overlie each other in several rows, it often happens that the outer ones do not produce flowers, that is, are empty or sterile. In the artichoke the outer imbricated scales or bracts are in this condition, and it is from the membranous white scales or bracts (paleae) forming the choke attached to the edible receptacle that the flowers are produced. The sterile bracts of the daisy occasionally produce capitula, and give rise to the hen-and-chickens daisy. In place of developing flower-buds, bracts may, in certain circumstances, as in proliferous or viviparous plants, produce leaf-buds. A sheathing bract enclosing one or several flowers is called a spathe. It is common among Monocotyledons, as Narcissus (fig. 4), snow-flake, Arum and palms. In some palms it is 20 ft. long, and encloses 200,000 flowers. It is often associated with that form of inflorescence termed the spadix, and may be coloured, as in Anthurium, or white, as in arum lily (Richardia aethiopica). When the spadix is compound or branching, as in palms, there are smaller spathes, surrounding separate parts of the inflorescence. The spathe protects the flowers in their young state, and often falls off after they are developed, or hangs down type of seed-plants, the micro- or macro-sporophylls are generally associated, often in large numbers, in separate cones, to which the term " flower " has been applied. But there is considerable difference of opinion as to the relation between these cones and the more definite and elaborate structure known as the flower in the higher group of seed-plants—the Angiosperms (q.v.) —and it is to this more definite structure that we generally refer in using the term " flower." Flowers are produced from flower-buds, just as leaf-shoots arise from leaf-buds. These two kinds of buds have a resemblance to each other as regards the arrangement and the development of their parts; and it sometimes happens, from injury and other causes, that the part of the axis which, in ordinary cases, would produce a leaf-bud, gives origin to a flower-bud. A flower-bud has not in ordinary circumstances any power of extension by the continuous development of its apex. In this respect it differs from a leaf-bud. In some cases, however, of monstrosity, especially seen in the rose (fig. I), the central part is pro-longed, and bears leaves or flowers. In such cases the flowers, so far as their functional capabilities are concerned, are usually abortive. This phenomenon is known as proliferation of the floral axis. Flower-buds, like leaf-buds, are produced in the axil of leaves, which are called bracts. The term bract is properly applied to the leaf from which the primary erects. floral axis, whether p, Petals multiplied at the expense of the stamens, which are reduced in number. Coloured leaves representing abortive carpels. a, Axis prolonged, bearing an imperfect flower at its apex. c, From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer. in a withered form, as in some palms, Typha and Pothos. In grasses the outer scales or glumes of the spikelets are sterile bracts (fig. 5, gl); and in Cyperaceae bracts enclose the organs of reproduction. Bracts are frequently changed into complete leaves. This change is called phyllody of bracts, and is seen in specie's of Plantago, especially in the variety of Plantago media, called the rose-plantain in gardens, where the bracts become leafy and form a rosette round the flowering axis. Similar changes occur in Plantago major, P. lanceolata, Ajuga reptans, dandelion, daisy, dahlia and in umbelliferous plants. The conversion of bracts into stamens (staminody of bracts) has been observed in the case of Abies excelsa. A lengthening of the axis of the female strobilus of Coniferae is not of infrequent occurrence in Cryptomeria japonica, larch (Larix europaea), &c., and this is usually associated with a leaf-like condition of the bracts, and sometimes even with the development of leaf-bearing shoots in place of the scales. The arrangement of the flowers on the axis, or the ramification of the floral axis, is called the inflorescence. The primary axis of the inflorescence is some-times called the rachis; its branches, whether terminal or lateral, which form the stalks supporting flowers or clusters of flowers, are peduncles, and if small branches are given off by it, they are called pedicels. A flower having a stalk is called pedunculate or pedicel- late; one having no stalk is sessile. In describing a branching inflorescence, it is common to speak of the rachis as the primary floral axis, its branches as the secondary floral axes, their divisions as the tertiary floral axes, and so on; thus avoiding any confusion that might arise from the use of the terms rachis, peduncle and pedicel. The peduncle is simple, bearing a single flower, as in primrose; or branched, as in London-pride. It is sometimes succulent, as in the cashew, in which it forms the large coloured expansion sup- porting the nut; spiral, as in Cyclamen and Vallisneria; or spiny, as in Alyssum spinosum. When the peduncle proceeds from radical leaves, that is, from an axis which is so shortened as to bring the leaves close together in the form of a cluster, as in the primrose, auricula or hyacinth, it is termed a scape. The floral axis may be shortened, assuming a flattened, convex or concave to:m, and bearing numerous flowers, as in the arti- choke, daisy and fig (fig. 6). The floral axis sometimes appears as if formed by several peduncles united together, constituting a fasciated axis, as in the cocks-comb, in which the flowers form a peculiar crest at the apex of the flattened peduncles. Adhesions occasionally take place between the peduncle and the bracts or leaves of the plant, as in the lime-tree (fig. 7). The' adhesion of the peduncles to the stem accounts for the extraaxillary position of flowers, as in many Solanaceae. When this union extends for a considerable length along the stem, several leaves may be interposed between the part where the peduncle becomes free and the leaf whence it originated, and it may be difficult to trace the connexion. The peduncle occasion-ally becomes abortive, and in place of bearing a flower, is trans-formed into a tendril; at other times it is hollowed at the apex, so as apparently to form the lower part of the outer whorl of floral leaves as in Eschscholtzia. The termination of the peduncle, or the part on which the whorls of the flower are arranged, is called the thalamus, torus or receptacle. There are two distinct types of inflorescence—one in which the flowers arise as lateral shoots from a primary axis, which goes on elongating, and the lateral shoots never exceed in their development the length of the primary axis beyond their point of origin. The flowers are thus always axillary. Exceptions, such as in cruciferous plants, are due to the non-appearance of the bracts. In the other type the primary axis terminates in a single flower, but lateral axes are given• off from the axils of the bracts, which again repeat the primary axis; the development of each lateral axis is stronger than that of the primary (From Strasburger's Lehrbuch axis beyond its point of origin. The der Botanik, by permission of Gustav Fischer.) flowers produced in this inflorescence striata. d, bract. of inflorescence is indeterminate, indefinite or axillory. Here the axis is either elongated, 6.-Peduncle of Fig Carica), ending in a receptacle, enclosing numerous male and female flowers. Fm. (Ficus hollow (From Vines' Students' Text-Book of Botany, by per-mission of Swan Sonnenschein & Co,) ;x a a, Branch. b, Petiole with axillary bud. Attached to the peduncle is the bract (h). k, Calyx. c, Corolla. s, Stamens. f, Ovary. kn, Flower-bud. Inflorescence. producing flower-buds as it grows, the lower expanding first (fig. 8), or it is shortened and depressed, and the outer flowers expand first (fig. 9). The expansion of the flowers is thus centripetal, that is, from base to apex, or from circumference to centre. The second kind of inflorescence is determinate, definite or terminal. In this the axis is either elongated and ends in a solitary flower, which thus terminates the axis, and if other flowers are produced, they belong to secondary axes farther from the centre; or the axis is shortened and flat- , producing a number of separate floral axes, the central one expanding first, while the others are developed in succession farther from the centre. The expansion of the flowers is in this case centrifugal, that is, from apex to base, or from centre to circumference. It is illustrated in fig. ro, Ranunculus bulbosus ; a' is the primary axis swollen at the base in a bulb-like manner b, and with roots proceeding from it. From the leaves which are radical proceeds the axis ending in a solitary terminal flower f'. About the middle of this axis there is a leaf or bract, from which a secondary floral axis a" is produced, ending in a single flower f", less advanced than the flower f. This secondary axis bears a leaf also, from which a tertiary floral axis a"' is produced, bearing an unexpanded solitary flower f'. From this tertiary axis a fourth is in progress of formation. Here f' is the termination of the primary axis, and this flower expands first, while the other flowers are developed centrifugally on separate axes. A third series of inflorescences, termed mixed, may be recognized. In them the primary axis has an arrangement belonging to the opposite type from that of the branches, or vice versa. According to the mode and degree of development of the lateral shoots and also of the bracts, various forms of both inflorescences result. Amongst indefinite forms the simplest occurs when a lateral shoot produced in the axil of a large single foliage leaf of the plant ends in a single flower, the axis of the plant elongating beyond, as in Veronica hederifolia, Vinca minor and Lysimachia nemorum. The flower in this case is solitary, and the ordinary leaves become bracts by producing flower-buds in place of leaf-buds; their number, like that of the leaves of this main axis, is indefinite, varying with the vigour of the plant. Usually, however, the floral axis, arising from a more or less altered leaf or bract, instead of ending in a solitary flower, is prolonged, and bears numerous bracteoles, from which smaller peduncles are produced, and those again in their turn may be branched in a similar way. Thus the flowers are arranged in groups, and frequently very complicated forms of inflorescence result. When the primary peduncle or floral axis, as in fig. 8, is elongated, and gives off pedicels, ending in single flowers, a raceme is produced, as in currant, hyacinth and barberry. If the secondary floral axes give rise to tertiary ones, the raceme is branching, and forms a panicle, as in Yucca gloriosa. If in a raceme the lower flower-stalks are developed more strongly than the upper, and thus all the flowers are nearly on a level, a corymb is formed,which maybe simple, as in fig. r r, where the primary axis a' gives off secondary axes a", a", which end in single flowers; or branching, where the secondary axes again subdivide. If the pedicels are very short or wanting, so that the flowers are sessile, a spike is produced, as in Plantago and vervain (Verbena offieinalis) (fig. 12). If the spike bears unisexual flowers, as in willow or hazel (fig. 13), it is an amentum or catkin, hence such trees are called amentiferous; atother times it becomes succulent, bearing numerous flowers, surrounded by a sheathing bract or spathe, and then it constitutes a spadix, which may be simple, as in Arum maculatum (fig. 14), or branching as in palms. A spike bearing female flowers only, and covered with scales, is a strobilus, as in the hop. In grasses there are usually numerous sessile flowers arranged in small spikes, called locustae or spikelets, which are either set closely along a central axis, or produced on secondary axes formed by the branching of the central one; to the latter form the term panicle is applied. If the primary axis, in place of being elongated, is contracted, it gives rise to other forms of indefinite inflorescence. When the axis is so shortened that the secondary axes arise from a common point, and spread out as radii of nearly equal length, each ending in a single flower or dividing again in a similar radiating manner, (From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.) an umbel is produced, as in fig. 15. From the primary floral axis a the secondary axes come off in a radiating or umbrella-like manner, and end in small umbels b, which are called partial umbels or umbellules. This inflorescence is seen in hemlock and other allied plants, which are hence called umbelliferous. If there are numerous flowers on a flattened, convex or slightly concave receptacle, having either very short pedicels or none, a capitulum (head) is formed, as in dandelion, daisy and other composite plants (fig. 2), also in scabious (fig. 9) and teazel. In the American button-bush the heads are globular, in some species of teazel elliptical, while in scabious and in composite plants, as sunflower, dandelion, thistle, centaury and marigold, they are somewhat hemispherical, with a flattened, slightly hollowed, or convex disk. If the margins of such a receptacle be developed upwards, the centre not developing, a concave receptacle is formed, which may partially or completely enclose a number of flowers that are generally unisexual. This gives rise to the peculiar inflorescence of Dorstenia, or to that of the fig (fig. 6), where the flowers are placed on the inner surface of the hollow receptacle, and are provided with bracteoles. This in-florescence has been called a hypanthodium. Lastly, we have what are called compound indefinite inflorescences. In these forms the lateral shoots, developed centripetally upon the primary axis, bear numerous bracteoles, from which floral shoots arise which may have a centripetal arrangement similar to that on the mother shoot, or it may be different. Thus we may have a group of racemes, arranged in a racemose manner on a common axis, forming a raceme of racemes or compound raceme, as in Astilbe. In the same way we may have compound umbels, as in hemlock and most Umbelliferae (fig. 15), a compound spike, as in rye-grass, a compound spadix, as in some palms, and a compound capitulum, as in the hen-and-chickens daisy. Again, there may be a raceme of capitula, that is, a group of capitula disposed in a racemose manner, as in Petasites, a raceme of umbels, as in ivy, and so on, all the forms of inflorescence being indefinite in disposition. In Eryngium the shortening of the pedicels changes an umbel into a capitulum. The simplest form of the definite type of the inflorescence is seen in Anemone nemorosa and in gentianella (Gentiana acaulis), where the axis terminates in a single flower, no other flowers being produced upon the plant. This is a solitary terminal inflorescence. If other flowers were produced, they would arise as lateral shoots from the bracts below the first-formed flower. The general name of cyme is applied to the arrangement of a group of flowers in a definite inflorescence. A cymose inflorescence is an inflorescence where the primary floral axis before terminating in a flower gives off one or more lateral unifloral axes which repeat the process—the development being only limited by the vigour of the plant. The floral axes are thus centrifugally developed. The cyme, according to its development, has been characterized as biparous or uniparous. In fig. 16 the biparous cyme is represented in the flowering branch of Cerastium. Here the primary axis t ends in a flower, which has passed into the state of fruit. At its base two leaves are produced, in each of which arise secondary axes t' t', ending in single flowers, and at the base of these axes a pair of opposite leaves is produced, giving rise to tertiary axes t" t", ending in single flowers, and so on. The term dichasium has also been applied to this form of cyme. In the natural order Carophyllaceae (pink family) the dichasial form of inflorescence is very general. In some members of the order, as Dianthus barbatus, D. carthusianorum, &c., in which the peduncles are 'short, and the flowers closely approximated, with a centrifugal expansion, the inflorescence has the form of a contracted dichasium, and receives the name of fascicle. When the axes become very much shortened, the arrangement is more complicated in appearance, and the nature of the inflorescence can only be recognized by the order of opening of the flowers. In Labiate plants, as the dead-nettle (Lamium), the flowers are produced in the axil of each of the foliage leaves of the plant, and they appear as if arranged in a simple whorl of flowers. But on examination it is found that there is a central flower expanding first, and from its axis two secondary axes spring bearing solitary flowers; the expansion is thus centrifugal. The inflorescence is therefore a contracted dichasium, the flowers being sessile, or nearly so, and the clusters are called verticillasters (fig. 17). Sometimes, especially towards the summit of a dichasium, owing to the exhaustion of the growing power of the plant, only one of the bracts gives origin to a new axis, the otherremaining empty; thus the inflorescence becomes unilateral, and further development is arrested. In addition to the dichasial form there are others where more than two lateral axes are produced from the primary floral axis, each of which in turn (From Strasburger's Lehrbuch der Botanik, by permission of Gustav Fischer.) t-t"", successive axes. (After Duchartre.) produces numerous axes. To this form the terms trichasial and polychasial cyme have been applied; but these are now usually designated cymose umbels. They are well seen in some species of Euphorbia. Another term, anthela, has been used to distinguish such forms as occur in several species of Luzula and /uncus, where numerous lateral axes arising from the primary axis grow very strongly and develop in an irregular manner. In the uniparous cyme a number of floral axes are successively developed one from the other, but the axis of each successive generation, instead of producing a pair of bracts, produces only one. The basal portion of the consecutive axes may become much thickened and arranged more or less in a straight line, and thus collectively form an apparent or false axis or sympodium, and the inflorescence thus simulates a raceme. In the true raceme, however, we find only a single axis, producing in succession a series of bracts, from which the floral peduncles arise as lateral shoots, and thus each flower is on the same side of the floral axis as the bract in the axil of which it is developed; but in the uniparous cyme the flower of each of these axes, the basal portions of which unite to form the false axis, is situated on the opposite side of the axis to the bract from which it apparently arises (fig. 18). The bract is not, however, the one from which the axis terminating in the flower arises, but is a bract produced upon it, and gives origin in its axil to a new axis, the basal portion of which, constituting the next part of the false axis, occupies the angle between this bract and its parent axis--the bract from which the axis really does arise being situated lower down upon the same side of the axis with itself. The uniparous cyme presents two forms, the scorpioid or cicinal and the helicoid or bostrychoid. In the scorpioid cyme the flowers are arranged alternately in a double row along one side of the false axis (fig. 1q), the bracts when developed forming a second double row on the opposite side; the whole inflorescence usually curves on itself like a scorpion's tail, hence its name. In fig. 20 is shown a diagrammatic sketch of this arrangement. The false axis, a b c d, is formed by successive generations of unifloral axes, the flowers being arranged along one side alternately and in a double row; had the bracts been developed they would have formed a similar double row on the opposite side of the false axis; the wholeinflorescence is represented as curved on itself. The inflorescence in the family Boraginaceae are usually regarded as true scorpioid cymes. In the helicoid cyme there is also a false axis formed by the basal portion of the separate axes, but the flowers are not placed in a double row, but in a single row, and form a spiral or helix round the false axis. In Alstroemeria, as represented in fig. 18, the axis al ends in a flower (cut off in the figure) and bears a leaf. From the axil of this leaf, that is, between it and the primary axis al arises a secondary axis a2, ending in a flower f2, and producing a leaf about the middle. From the axil of this leaf a tertiary floral axis a3, ending in a flower f3, takes origin. In this case the axes are not arranged in two rows along one side of the false axis, but are placed at regular intervals, so as to form an elongated spiral round it. Compound definite inflorescences are by no means common, but in Streptocarpus polyanthus and in several calceolarias we probably have examples. Here there are scorpioid cymes of pairs of flowers, each pair consisting of an older and a younger flower. Forms of inflorescence occur, in which both the definite and indefinite types are represented—mixed inflorescences. Thus in Composite plants,such as hawkweeds(Hieracia) and ragworts (Senecio, fig. 21), the heads of flowers, =reds. taken as a whole, are developed centrifugally, the cence. terminal head first, while the florets, or small flowers on the receptacle, open centripetally, those at the circumference first. So also in Labiatae, such as dead-nettle (Lamium), the different whorls of inflorescence are developed centripetally, while the florets of the verticillaster are centrifugal. This mixed character presents difficulties in such cases as Labiatae, where the leaves, in place of retaining their ordinary form, become bracts, and thus might lead to the supposition of the whole series of flowers being one inflorescence. In such cases the cymes are described as spiked, racemose, or panicled, according to circumstances. In Saxifraga umbrosa (London-pride) and in the horse-chestnut we meet with a raceme of scorpioid cymes; in sea-pink, a capitulum of contracted scorpioid cymes (often called a glomerulus); in laurustinus, a compound umbel of dichasial cymes; a scorpioid cyme of capitula in Vernonia scorpioides. The so-called catkins of the birch are, in reality, spikes of contracted dichasial cymes. In the bell-flower (Campanula) there is a racemose uniparous cyme. In the privet (Ligustrum vulgare) there are numerous racemes of dichasia arranged in a racemose manner along an axis; the whole inflorescence thus has an appearance not unlike a bunch of grapes, and has been called a thyrsus.
End of Article: FLOWER (Lat. flos, floris; Fr. fleur)
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