Chapter 9

(G. F. Z.)

FLOURENS, GUSTAVE(1838-1871), French revolutionist and writer, a son of J.P. Flourens (1794-1867), the physiologist, was born at Paris on the 4th of August 1838. In 1863 he undertook for his father a course of lectures at the Collège de France, the subject of which was the history of mankind. His theories as to the manifold origin of the human race, however, gave offence to the clergy, and he was precluded from delivering a second course. He then went to Brussels, where he published his lectures under the title ofHistoire de l’homme(1863); he next visited Constantinople and Athens, took part in the Cretan insurrection of 1866, spent some time in Italy, where an article of his in thePopolo d’Italiacaused his arrest and imprisonment, and finally, having returned to France, nearly lost his life in a duel with Paul de Cassagnac, editor of thePays. In Paris he devoted his pen to the cause of republicanism, and at length, having failed in an attempt to organize a revolution at Belleville on the 7th of February 1870, found himself compelled to flee from France. Returning to Paris on the downfall of Napoleon, he soon placed himself at the head of a body of 500 tirailleurs. On account of his insurrectionary proceedings he was taken prisoner at Créteil, near Vincennes, by the provisional government, and confined at Mazas on the 7th of December 1870, but was released by his men on the night of January 21-22. On the 18th of March he joined the Communists. He was elected a member of the commune by the 20th arrondissement, and was named colonel. He was one of the most active leaders of the insurrection, and in a sortie against the Versailles troops in the morning of the 3rd of April was killed in a hand-to-hand conflict at Rueil, near Malmaison. Besides hisScience de l’homme(Paris, 1869), Gustave Flourens was the author of numerous fugitive pamphlets.

See C. Prolès,Les Hommes de la révolution de 1871(Paris, 1898).

FLOURENS, MARIE JEAN PIERRE(1794-1867), French physiologist, was born at Maureilhan, near Béziers, in the department of Hérault, on the 15th of April 1794. At the age of fifteen he began the study of medicine at Montpellier, where in 1823 he received the degree of doctor. In the following year he repaired to Paris, provided with an introduction from A.P. de Candolle, the botanist, to Baron Cuvier, who received him kindly, and interested himself in his welfare. At Paris Flourens engaged in physiological research, occasionally contributing to literary publications; and in 1821, at the Athénée there, he gave a course of lectures on the physiological theory of the sensations, which attracted much attention amongst men of science. His paper entitledRecherches expérimentales sur les propriétés et les fonctions du système nerveux dans les animaux vertébrés, in which he, from experimental evidence, sought to assign their special functions to the cerebrum, corpora quadrigemina and cerebellum, was the subject of a highly commendatory report by Cuvier, adopted by the French Academy of Sciences in 1822. He was chosen by Cuvier in 1828 to deliver for him a course of lectures on natural history at the Collège de France, and in the same year became, in succession to L.A.G. Bosc, a member of the Institute, in the division “Économie rurale.” In 1830 he became Cuvier’s substitute as lecturer on human anatomy at the Jardin du Roi, and in 1832 was elected to the post of titular professor, which he vacated for the professorship of comparative anatomy created for him at the museum of the Jardin the same year. In 1833 Flourens, in accordance with the dying request of Cuvier, was appointed a perpetual secretary of the Academy of Sciences; and in 1838 he was returned as a deputy for the arrondissement of Béziers. In 1840 he was elected, in preference to Victor Hugo, to succeed J.F. Michaud at the French Academy; and in 1845 he was created a commander of the legion of honour, and in the next year a peer of France. In March 1847 Flourens directed the attention of the Academy of Sciences to the anaesthetic effect of chloroform on animals. On the revolution of 1848 he withdrew completely from political life; and in 1855 he accepted the professorship of natural history at the Collège de France. He died at Montgeron, near Paris, on the 6th of December 1867.

Besides numerous shorter scientific memoirs, Flourens published—Essai sur quelques points de la doctrine de la révulsion et de la dérivation(Montpellier, 1813);Expériences sur le système nerveux(Paris, 1825);Cours sur la génération, l’ovologie, et l’embryologie(1836);Analyse raisonnée des travaux de G. Cuvier(1841);Recherches sur le développement des os et des dents(1842);Anatomie générale de la peau et des membranes muqueuses(1843);Buffon, histoire de ses travaux et de ses idées(1844);Fontenelle, ou de la philosophie moderne relativement aux sciences physiques(1847);Théorie expérimentale de la formation des os(1847);Œuvres complètes de Buffon(1853);De la longévité humaine et de la quantité de vie sur le globe(1854), numerous editions;Histoire de la découverte de la circulation du sang(1854);Cours de physiologie comparée(1856);Recueil des éloges historiques(1856);De la vie et de l’intelligence(1858);De la raison, du génie, et de la folie(1861);Ontologie naturelle(1861);Examen du livre de M. Darwin sur l’Origine des Espèces(1864). For a list of his papers see the Royal Society’sCatalogue of Scientific Papers.

FLOWER, SIR WILLIAM HENRY(1831-1899), English biologist, was born at Stratford-on-Avon on the 30th of November 1831. Choosing medicine as his profession, he began his studies at University College, London, where he showed special aptitude for physiology and comparative anatomy and took his M.B. degree in 1851. He then joined the Army Medical Service, and went out to the Crimea as assistant-surgeon, receiving the medal with four clasps. On his return to England he became a member of the surgical staff of the Middlesex hospital, London, and in 1861 succeeded J.T. Quekett as curator of the Hunterian Museum of the Royal College of Surgeons of England. In 1870 he also became Hunterian professor, and in 1884, on the death of Sir Richard Owen, was appointed to the directorship of the Natural History Museum at South Kensington. He died in London on the 1st of July 1899. He made valuable contributions to structural anthropology, publishing, for example, complete and accurate measurements of no less than 1300 human skulls, and as a comparative anatomist he ranked high, devoting himself especially to the study of the mammalia. He was also a leading authority on the arrangement of museums. The greater part of his life was spent in their administration, and in consequence he held very decided views as to the principles upon which their specimens should be set out. He insisted on the importance of distinguishing between collections intended for the use of specialists and those designed for the instruction of the general public, pointing out that it was as futile to present to the former a number of merely typical forms as to provide the latter with a long series of specimens differing only in the most minute details. His ideas, which were largely and successfully applied to the museums of which he had charge, gained wide approval, and their influence entitles him to be looked upon as a reformer who did much to improve the methods of museum arrangement and management. In addition to numerous original papers, he was the author ofAn Introduction to the Osteology of the Mammalia(1870);Fashion in Deformity(1881);The Horse: a Study in Natural History(1890);Introduction to the Study of Mammals, Living and Extinct(1891);Essays on Museums and other Subjects(1898). He also wrote many articles for the ninth edition of theEncyclopaedia Britannica.

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 of 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 botanical 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 orstamenand the ovule-bearer orcarpel. 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 megaspore, which is contained in the ovule or megasporangium.

In Gymnosperms (q.v.), which represent the more primitivetype 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.”

s, Sepals transformed into leaves.

p, Petals multiplied at the expense of the stamens, which are reduced in number.

c, Coloured leaves representing abortive carpels.

a, Axis prolonged, bearing an imperfect flower at its apex.

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. 1), the central part is prolonged, 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 calledbracts.

The termbractis properly applied to the leaf from which the primary floral axis, whether simple or branched, arises, while the leaves which arise on the axis between the bract and the outer envelope of the flowerBracts.arebracteolesorbractlets. Bracts sometimes do not differ from the ordinary leaves, as inVeronica hederifolia,Vinca,AnagallisandAjuga. 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 ofDianthusand winter aconite (Eranthis), where they have received the name ofepicalyxorcalyculus. 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 inAmherstia nobilis,Euphorbia splendens,Erica elegansandSalvia 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 theebracteateinflorescence 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 ofSalvia 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 occasionally persistent, remaining long attached to the base of the peduncles, but more usually they are deciduous, falling off early by 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 the pine-apple are of the same nature. At the base of the general umbel in umbelliferous plants a whorl of bracts often exists, called ageneral involucre, and at the base of the smaller umbels or umbellules there is a similar leafy whorl called aninvolucelorpartial 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. 15), 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 (gamophyllous), as in many species ofBupleurumand inLavatera. 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 thecupuleor 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 aspathe. It is common among Monocotyledons, asNarcissus(fig. 4), snow-flake,Arumand palms. In some palms it is 20 ft. long, and encloses 200,000 flowers. It is often associated with that form of inflorescence termed thespadix, and may be coloured, as inAnthurium, 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 downin a withered form, as in some palms,TyphaandPothos. 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 calledphyllodyof bracts, and is seen in species ofPlantago, especially in the variety ofPlantago media, called the rose-plantain in gardens, where the bracts become leafy and form a rosette round the flowering axis. Similar changes occur inPlantago major,P. lanceolata,Ajuga reptans, dandelion, daisy, dahlia and in umbelliferous plants. The conversion of bracts into stamens (staminodyof bracts) has been observed in the case ofAbies excelsa. A lengthening of the axis of the female strobilus of Coniferae is not of infrequent occurrence inCryptomeria 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 theinflorescence. The primary axis of the inflorescence is sometimes called therachis; its branches, whether terminal or lateral, which form the stalks supporting flowers or clusters of flowers, arepeduncles, and if small branches are given off by it, they are calledpedicels. A flower having a stalk is calledpedunculateorpedicellate; one having no stalk issessile. In describing a branching inflorescence, it is common to speak of the rachis as theprimaryfloral axis, its branches as thesecondaryfloral axes, their divisions as thetertiaryfloral axes, and so on; thus avoiding any confusion that might arise from the use of the termsrachis,peduncleandpedicel.

Thepeduncleis 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 supporting the nut; spiral, as inCyclamenandVallisneria; or spiny, as inAlyssum 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 ascape. The floral axis may be shortened, assuming a flattened, convex or concave form, and bearing numerous flowers, as in the artichoke, 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 cockscomb, 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 extra-axillary 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 occasionally becomes abortive, and in place of bearing a flower, is transformed 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 inEschscholtzia. The termination of the peduncle, or the part on which the whorls of the flower are arranged, is called thethalamus,torusorreceptacle.

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.

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 theInflorescence.primary axis beyond their point of origin. The flowers are thus alwaysaxillary. 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 axis beyond its point of origin. The flowers produced in this inflorescence are thusterminal. The first kind of inflorescence isindeterminate,indefiniteoraxillary. Here the axis is either elongated,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 thuscentripetal, that is, from base to apex, or from circumference to centre.

The second kind of inflorescence isdeterminate,definiteorterminal. 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 flattened, 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 casecentrifugal, that is, from apex to base, or from centre to circumference. It is illustrated in fig. 10,Ranunculus bulbosus;a′ is the primary axis swollen at the base in a bulb-like mannerb, and with roots proceeding from it. From the leaves which are radical proceeds the axis ending in a solitary terminal flowerf′. About the middle of this axis there is a leaf or bract, from which a secondary floral axisa″ is produced, ending in a single flowerf″, less advanced than the flowerf′. This secondary axis bears a leaf also, from which a tertiary floral axisa″′ is produced, bearing an unexpanded solitary flowerf″′. From this tertiary axis a fourth is in progress of formation. Heref′ 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, termedmixed, 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 inVeronica hederifolia,Vinca minorandLysimachia nemorum. The flower in this case issolitary, 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, aracemeis produced, as in currant, hyacinth and barberry. If the secondary floral axes give rise to tertiary ones, the raceme is branching, and forms apanicle, as inYucca 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, acorymbis formed, which may be simple, as in fig. 11, where the primary axisa′ gives off secondary axesa″,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, aspikeis produced, as inPlantagoand vervain (Verbena officinalis) (fig. 12). If the spike bears unisexual flowers, as in willow or hazel (fig. 13), it is anamentumorcatkin, hence such trees are calledamentiferous; at other times it becomes succulent, bearing numerous flowers, surrounded by a sheathing bract or spathe, and then it constitutes aspadix, which may be simple, as inArum maculatum(fig. 14), or branching as in palms. A spike bearing female flowers only, and covered with scales, is astrobilus, as in the hop. In grasses there are usually numerous sessile flowers arranged in small spikes, calledlocustaeorspikelets, 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.

Fig. 11.—Corymb ofCerasus Mahaleb, terminating an abortive branch, at the base of which are modified leaves in the form of scales,e.a′, Primary axis;a″, secondary axes bearing flowers;b, bract in the axils of which the secondary axes arise.

Fig. 12.—Spike of Vervain (Verbena officinalis), showing sessile flowers on a common rachis. The flowers at the lower part of the spike have passed into fruit, those towards the middle are in full bloom, and those at the top are only in bud.

Fig. 13.—Amentum or catkin of Hazel (Corylus Avellana), consisting of an axis or rachis covered with bracts in the form of scales, each of which covers a male flower, the stamens of which are seen projecting beyond the scale. The catkin falls off in a mass, separating from the branch by an articulation.

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 asradiiof nearly equal length, each ending in a single flower or dividing again in a similar radiating manner, anumbelis 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 umbelsb, which are calledpartial umbelsorumbellules. 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, acapitulum(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 ofDorstenia, 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 inflorescence has been called ahypanthodium.

Lastly, we have what are calledcompound indefiniteinflorescences. 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 inAstilbe. 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 inPetasites, a raceme of umbels, as in ivy, and so on, all the forms of inflorescence being indefinite in disposition. InEryngiumthe shortening of the pedicels changes an umbel into a capitulum.

The simplest form of the definite type of the inflorescence is seen inAnemone nemorosaand in gentianella (Gentiana acaulis), where the axis terminates in a single flower, no other flowers being produced upon the plant. This is asolitary terminalinflorescence. If other flowers were produced, they would arise as lateral shoots from the bracts below the first-formed flower. The general name ofcymeis applied to the arrangement of a group of flowers in a definite inflorescence. Acymoseinflorescence 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 asbiparousoruniparous. In fig. 16 the biparous cyme is represented in the flowering branch ofCerastium. Here the primary axistends in a flower, which has passed into the state of fruit. At its base two leaves are produced, in each of which arise secondary axest′t′, ending in single flowers, and at the base of these axes a pair of opposite leaves is produced, giving rise to tertiary axest″t″, ending in single flowers, and so on. The termdichasiumhas 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, asDianthus 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 offascicle. 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 calledverticillasters(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 other remaining 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 produces numerous axes. To this form the termstrichasialandpolychasial cymehave been applied; but these are now usually designatedcymose umbels. They are well seen in some species ofEuphorbia. Another term,anthela, has been used to distinguish such forms as occur in several species ofLuzulaandJuncus, 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 orsympodium, 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, thescorpioidorcicinaland thehelicoidorbostrychoid.

Fig. 18.—Helicoid cyme of a species ofAlstroemeria.a1,a2,a3,a4, &c., separate axes successively developed in the axils of the corresponding bractsb2,b3,b4, &c., and ending in a flowerf2,f3,f4, &c. The whole appears to form a simple raceme of which the axes form the internodes.

Fig. 19.—Scorpioidal or cicinal cyme of Forget-me-not (Myosotis palustris).

Fig. 20.—Diagram of definite floral axesa,b,c,d,e, &c.

Fig. 21.—Flowering stalk of Ragwort (Senecio). The flowers are in heads (capitula), and open from the circumference inwards in an indefinite centripetal manner. The heads of flowers, on the other hand, taken collectively, expand centrifugally—the central one a first.

In the scorpioid cyme the flowers are arranged alternately in a double row along one side of the false axis (fig. 19), 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 whole inflorescence 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. InAlstroemeria, as represented in fig. 18, the axisa1ends 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 axisa1arises a secondary axisa2, ending in a flowerf2, and producing a leaf about the middle. From the axil of this leaf a tertiary floral axisa3, ending in a flowerf3, 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 inStreptocarpus polyanthusand in several calceolarias we probably have examples. Here there arescorpioid 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—mixedinflorescences. Thus in Composite plants, such as hawk weeds (Hieracia) and ragworts (Senecio, fig. 21), theheadsof flowers,Mixed inflorescence.taken as a whole, are developed centrifugally, the terminal head first, while theflorets, 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. InSaxifraga 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 inVernonia 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 athyrsus.

Tabular View of Inflorescences

A. Indefinite Centripetal Inflorescence.I. Flowers solitary, axillary.Vinca,Veronica hederifolia.II. Flowers in groups, pedicellate.1. Elongated form (Raceme),Hyacinth,Laburnum,Currant. (Corymb),Ornithogalum.2. Contracted or shortened form (Umbel),Cowslip,Astrantia.III. Flowers in groups, sessile.1. Elongated form (Spike),Plantago.(Spikelet),Grasses.(Amentum, Catkin),Willow,Hazel.(Spadix)Arum, somePalms.(Strobilus),Hop.2. Contracted or shortened form (Capitulum),Daisy,Dandelion,Scabious.IV. Compound Indefinite Inflorescence.a. Compound Spike,Rye-grass.b. Compound Spadix,Palms.c. Compound Raceme,Astilbe.d. Compound Umbel,Hemlockand mostUmbelliferae.e. Raceme of Capitula,Petasites.f. Raceme of Umbels,Ivy.B. Definite Centrifugal Inflorescence.I. Flowers solitary, terminal.Gentianella,Tulip.II. Flowers in Cymes.1. Uniparous Cyme.a. Helicoid Cyme (axes forming a spiral).Elongated form,Alstromeria.Contracted form,Witsenia corymbosa.b. Scorpioid Cyme (axes unilateral, two rows).Elongated form,Forget-me-not,Symphytum,Henbane.Contracted form,Erodium,Alchemilla arvensis.2. Biparous Cyme (Dichotomous), including 3-5 chotomous Cymes (Dichasium, Cymose Umbel, Anthela).a. Elongated form,Cerastium,Stellaria.b. Contracted form (Verticillaster),Dead-nettle,Pelargonium.3. Compound Definite Inflorescence.Streptocarpus polyanthus, manyCalceolarias.C. Mixed Inflorescence.Raceme of Scorpioid Cymes,Horse-chestnut.Scorpioid Cyme of Capitula,Vernonia scorpioides.Compound Umbel of Dichotomous Cymes,Laurustinus.Capitulum of contracted Scorpioid Cymes (Glomerulus),Sea-pink.

A. Indefinite Centripetal Inflorescence.

I. Flowers solitary, axillary.Vinca,Veronica hederifolia.

II. Flowers in groups, pedicellate.

1. Elongated form (Raceme),Hyacinth,Laburnum,Currant. (Corymb),Ornithogalum.2. Contracted or shortened form (Umbel),Cowslip,Astrantia.

1. Elongated form (Raceme),Hyacinth,Laburnum,Currant. (Corymb),Ornithogalum.

2. Contracted or shortened form (Umbel),Cowslip,Astrantia.

III. Flowers in groups, sessile.

1. Elongated form (Spike),Plantago.(Spikelet),Grasses.(Amentum, Catkin),Willow,Hazel.(Spadix)Arum, somePalms.(Strobilus),Hop.2. Contracted or shortened form (Capitulum),Daisy,Dandelion,Scabious.

1. Elongated form (Spike),Plantago.(Spikelet),Grasses.(Amentum, Catkin),Willow,Hazel.(Spadix)Arum, somePalms.(Strobilus),Hop.

2. Contracted or shortened form (Capitulum),Daisy,Dandelion,Scabious.

IV. Compound Indefinite Inflorescence.

a. Compound Spike,Rye-grass.b. Compound Spadix,Palms.c. Compound Raceme,Astilbe.d. Compound Umbel,Hemlockand mostUmbelliferae.e. Raceme of Capitula,Petasites.f. Raceme of Umbels,Ivy.

a. Compound Spike,Rye-grass.

b. Compound Spadix,Palms.

c. Compound Raceme,Astilbe.

d. Compound Umbel,Hemlockand mostUmbelliferae.

e. Raceme of Capitula,Petasites.

f. Raceme of Umbels,Ivy.

B. Definite Centrifugal Inflorescence.

I. Flowers solitary, terminal.Gentianella,Tulip.

II. Flowers in Cymes.

1. Uniparous Cyme.

a. Helicoid Cyme (axes forming a spiral).Elongated form,Alstromeria.Contracted form,Witsenia corymbosa.b. Scorpioid Cyme (axes unilateral, two rows).Elongated form,Forget-me-not,Symphytum,Henbane.Contracted form,Erodium,Alchemilla arvensis.

a. Helicoid Cyme (axes forming a spiral).Elongated form,Alstromeria.Contracted form,Witsenia corymbosa.

b. Scorpioid Cyme (axes unilateral, two rows).Elongated form,Forget-me-not,Symphytum,Henbane.Contracted form,Erodium,Alchemilla arvensis.

2. Biparous Cyme (Dichotomous), including 3-5 chotomous Cymes (Dichasium, Cymose Umbel, Anthela).

a. Elongated form,Cerastium,Stellaria.b. Contracted form (Verticillaster),Dead-nettle,Pelargonium.

a. Elongated form,Cerastium,Stellaria.

b. Contracted form (Verticillaster),Dead-nettle,Pelargonium.

3. Compound Definite Inflorescence.Streptocarpus polyanthus, manyCalceolarias.

C. Mixed Inflorescence.

Raceme of Scorpioid Cymes,Horse-chestnut.Scorpioid Cyme of Capitula,Vernonia scorpioides.Compound Umbel of Dichotomous Cymes,Laurustinus.Capitulum of contracted Scorpioid Cymes (Glomerulus),Sea-pink.

Raceme of Scorpioid Cymes,Horse-chestnut.

Scorpioid Cyme of Capitula,Vernonia scorpioides.

Compound Umbel of Dichotomous Cymes,Laurustinus.

Capitulum of contracted Scorpioid Cymes (Glomerulus),Sea-pink.

Fig. 22.—Flower ofSedum rubens.s, Sepals;p, petals;a, stamens;c, carpels.

Fig. 23.—Diagram of a completely symmetrical flower, consisting of four whorls, each of five parts,s, Sepals;p, petals;a, stamens;c, carpels.

Fig. 24.—Monochlamydeous (apetalous) flower of Goosefoot (Chenopodium), consisting of a single perianth (calyx) of five parts, enclosing five stamens, which are opposite the divisions of the perianth, owing to the absence of the petals.

Fig. 25.—Stamen, consisting of a filament (stalk)fand an anthera, containing the pollenp, which is discharged through slits in the two lobes of the anther.

Fig. 26.—The pistil of Tobacco (Nicotiana Tabacum), consisting of the ovaryo, containing ovules, the styles, and the capitate stigmag. The pistil is placed on the receptacler, at the extremity of the peduncle.

The flower consists of the floral axis bearing the sporophylls (stamens and carpels), usually with certain protective envelopes. The axis is usually very much contracted, no internodes being developed, and the portion bearing the floral leaves, termedThe flower.thethalamusortorus, frequently expands into a conical, flattened or hollowed expansion; at other times, though rarely, the internodes are developed and it is elongated. Upon this torus the parts of the flower are arranged in a crowded manner, usually forming a series of verticils, the parts of which alternate; but they are sometimes arranged spirally especially if the floral axis be elongated. In a typical flower, as in fig. 22, we recognize four distinct whorls of leaves: an outer whorl, thecalyxofsepals; within it, another whorl, the parts alternating with those of the outer whorl, thecorollaofpetals; next a whorl of parts alternating with the parts of the corolla, theandroeciumofstamens; and in the centre thegynoeciumofcarpels. Fig. 23 is a diagrammatic representation of the arrangement of the parts of such a flower; it is known as afloral diagram. The flower is supposed to be cut transversely, and the parts of each whorl are distinguished by a different symbol. Of these whorls the two internal, forming the sporophylls, constitute theessentialorgans of reproduction; the two outer whorls are the protective coverings or floralenvelopes. The sepals are generally of a greenish colour; their function is mainly protective, shielding the more delicate internal organs before the flower opens. The petals are usually showy, and normally alternate with the sepals. Sometimes, as usually in monocotyledons, the calyx and corolla are similar; in such cases the termperianth, orperigone, is applied. Thus, in the tulip, crocus, lily, hyacinth, we speak of the parts of the perianth, in place of calyx and corolla, although in these plants there is an outer whorl (calyx), of three parts, and an inner (corolla), of a similar number, alternating with them. When the parts of the calyx are in appearance like petals they are said to bepetaloid, as in Liliaceae. In some cases the petals have the appearance of sepals, then they aresepaloid, as in Juncaceae. In plants, asNymphaea alba, where a spiral arrangement of the floral leaves occurs, it is not easy to say where the calyx ends and the corolla begins, as these two whorls pass insensibly into each other. When both calyx and corolla are present, the plants aredichlamydeous; when one only is present, the flower is termedmonochlamydeousorapetalous, having no petals (fig. 24). Sometimes both are absent, when the flower isachlamydeous, or naked, as in willow. The outermost series of the essential organs, collectively termed theandroecium, is composed of the microsporophylls known as the staminal leaves orstamens. In their most differentiated form each consists of a stalk, thefilament(fig. 25,f), supporting at its summit the anther (a), consisting of the pollen-sacs which contain the powderypollen(p), the microspores, which is ultimately discharged therefrom. Thegynoeciumorpistilis the central portion of the flower, terminating the floral axis. It consists of one or morecarpels(megasporophylls), either separate (fig. 22,c) or combined (fig. 24). The parts distinguished in the pistil are theovary(fig. 26,o), which is the lower portion enclosing theovulesdestined to become seeds, and thestigma(g), a portion of loose cellular tissue, the receptive surface on which the pollen is deposited, which is either sessile on the apex of the ovary, as in the poppy, or is separated from it by a prolonged portion called thestyle(s). The androecium and gynoecium are not present in all flowers. When both are present the flower ishermaphrodite; and in descriptive botany such a flower is indicated by the symbol ☿. When only one of those organs is present the flower isunisexualordiclinous, and is either male (staminate), ♁; or female (pistillate), ♀. A flower then normally consists of the four series of leaves—calyx, corolla, androecium and gynoecium—and when these are all present the flower iscomplete. These are usually densely crowded upon the thalamus, but in some instances, after apical growth has ceased in the axis, an elongation of portions of the receptacle by intercalary growth occurs, by which changes in the position of the parts may be brought about. Thus inLychnisan elongation of the axis betwixt the calyx and the corolla takes place, and in this way they are separated by an interval. Again, in the passion-flower (Passiflora) the stamens are separated from the corolla by an elongated portion of the axis, which has consequently been termed theandrophore, and inPassifloraalso, fraxinella (fig. 27), Capparidaceae, and some other plants, the ovary is raised upon a distinct stalk termed thegynophore; it is thus separated from the stamens, and is said to bestipitate. Usually the successive whorls of the flower, disposed from below upwards or from without inwards upon the floral axis, are of the same number of parts, or are a multiple of the same number of parts, those of one whorl alternating with those of the whorls next it.

In the more primitive types of flowers the torus is more or less convex, and the series of organs follow in regular succession, culminating in the carpels, in the formation of which the growth of the axis is closed (fig. 28). This arrangement is known as hypogynous, the other series (calyx, corolla and stamens) being beneath (hypo-) the gynoecium. In other cases, the apex of the growing point ceases to develop, and the parts below form a cup around it, from the rim of which the outer members of the flower are developed around (peri-) the carpels, which are formed from the apex of the growing-point at the bottom of the cup. This arrangement is known asperigynous(fig. 29). In many cases this is carried farther and a cavity is formed which is roofed overby the carpels, so that the outer members of the flower spring from the edge of the receptacle which is immediately above the ovary (epigynous), hence the term epigyny (fig. 30).

Fig. 33.—Diagrammatic section of a symmetrical pentamerous flower of Stone-crop (Sedum), consisting of five sepals (s), five petals (p) alternating with the sepals, ten stamens (a) in two rows, and five carpels (c) containing ovules. The dark lines (d) on the outside of the carpels are glands.

Fig. 34.—Diagram of the flower of Flax (Linum), consisting of five sepals (s), five petals (p), five stamens (a), and five carpels (c), each of which is partially divided into two. The dots represent a whorl of stamens which has disappeared. It is pentamerous, complete, symmetrical and regular.

Fig. 35.—Diagram of the flower of Heath (Erica), a regular tetramerous flower.

Fig. 36.—Diagram of the trimerous symmetrical flower of Iris.

Fig. 37.—Diagram of the symmetrical trimerous flower of Fritillary (Fritillaria).

Fig. 38.—Diagram of the flower of Saxifrage (Saxifraga tridactylites). The calyx and corolla consist of five parts, the stamens are ten in two rows, while the pistil has only two parts developed.

When a flower consists of parts arranged in whorls it is said to becyclic, and if all the whorls have an equal number of parts and are alternate it iseucyclic(figs. 22, 23). In contrast to the cyclic flowers are those, as in Magnoliaceae,Symmetry of the flower.where the parts are in spirals (acyclic). Flowers which are cyclic at one portion and spiral at another, as in many Ranunculaceae, are termedhemicyclic. In spiral flowers the distinction into series is by no means easy, and usually there is a gradual passage from sepaloid through petaloid to staminal parts, as in the water-lily family, Nymphaeaceae (figs. 31, 32), although in some plants there is no such distinction, the parts being all petaloid, as inTrollius. Normally, the parts of successive whorls alternate; but in some cases we find the parts of one whorl opposite orsuperposedto those of the next whorl. In some cases, as in the vine-family Ampelidaceae, this seems to be the ordinary mode of development, but the superposition of the stamens on the sepals in many plants, as in the pink family, Caryophyllaceae, is due to the suppression or abortion of the whorl of petals, and this idea is borne out by the development, in some plants of the order, of the suppressed whorl. As a rule, whenever we find the parts of one whorl superposed on those of another we may suspect some abnormality.

A flower is said to besymmetricalwhen each of its whorls consists of an equal number of parts, or when the parts of any one whorl are multiples of that preceding it. Thus, a symmetrical flower may have five sepals, five petals, five stamens and five carpels, or the number of any of these parts may be ten, twenty or some multiple of five. Fig. 23 is a diagram of a symmetrical flower, with five parts in each whorl, alternating with each other. Fig. 33 is a diagram of a symmetrical flower of stone-crop, with five sepals, five alternating petals, ten stamens and five carpels. Here the number of parts in the staminal whorl is double that in the others, and in such a case the additional five parts form a second row alternating with the others. In the staminal whorl especially it is common to find additional rows. Fig. 34 shows a symmetrical flower, with five parts in the three outer rows, and ten divisions in the inner. In this case it is the gynoecium which has an additional number of parts. Fig. 35 shows a flower of heath, with four divisions of the calyx and corolla, eight stamens in two rows, and four divisions of the pistil. In fig. 36 there are three parts in each whorl; and in fig. 37 there are three divisions of the calyx, corolla and pistil, and six stamens in two rows. In all these cases the flower is symmetrical. In Monocotyledons it is usual for the staminal whorl to be double, it rarely having more than two rows, whilst amongst dicotyledons there are often very numerous rows of stamens. The floral envelopes are rarely multiplied. Flowers in which the number of parts in each whorl is the same, areisomerous(of equal number); when the number in some of the whorls is different, the flower isanisomerous(of unequal number). The pistillate whorl is very liable to changes. It frequently happens that when it is fully formed, the number of its parts is not in conformity with that of the other whorls. In such circumstances, however, a flower has been called symmetrical, provided the parts of the other whorls are normal,—the permanent state of the pistil not being taken into account in determining symmetry. Thus fig. 38 shows a pentamerous symmetrical flower, with dimerous pistil. Symmetry, then, in botanical language, has reference to a certain definite numerical relation of parts. A flower in which the parts are arranged in twos is calleddimerous; when the parts of the whorls are three, four or five, the flower istrimerous,tetramerousorpentamerous, respectively. The symmetry which is most commonly met with is trimerous and pentamerous—the former occurring generally among monocotyledons, the latter among dicotyledons. Dimerous and tetramerous symmetry occur also among dicotyledons.

The various parts of the flower have a certain definite relation to the axis. Thus, in axillary tetramerous flowers (fig. 35), one sepal is next the axis, and is calledsuperiororposterior; another is next the bract, and isinferiororanterior, and the other two arelateral; and certain terms are used to indicate that position. A plane passing through the anterior and posterior sepal and through the floral axis is termed themedian planeof the flower; a plane cutting it at right angles, and passing through the lateral sepals, is thelateral plane; whilst the planes which bisect theangles formed by the lateral and median planes are thediagonal planes, and in these flowers the petals which alternate with the sepals are cut by the diagonal planes.

In a pentamerous flower one sepal may be superior, as in the calyx of Rosaceae and Labiatae; or it may be inferior, as in the calyx of Leguminosae (fig. 39)—the reverse, by the law of alternation, being the case with the petals. Thus, in the blossom of the pea (figs. 39, 40), the odd petal (vexillum)stis superior, while the odd sepal is inferior. In the order Scrophulariaceae one of the two carpels is posterior and the other anterior, whilst in Convolvulaceae the carpels are arranged laterally. Sometimes the twisting of a part makes a change in the position of other parts, as in Orchids, where the twisting of the ovary changes the position of the labellum.

When the different members of each whorl are like in size and shape, the flower is said to beregular; while differences in the size and shape of the parts of a whorl make the flowerirregular, as in the papilionaceous flower, represented in fig. 39. When a flower can be divided by a single plane into two exactly similar parts; then it is said to bezygomorphic. Such flowers as Papilionaceae, Labiatae, are examples. In contrast with this arepolysymmetricalor actinomorphic flowers, which have a radial symmetry and can be divided by several planes into several exactly similar portions; such are all regular, symmetrical flowers. When the parts of any whorl are not equal to or some multiple of the others, then the flower isasymmetrical. This want of symmetry may be brought about in various ways. Alteration in the symmetrical arrangement as well as in the completeness and regularity of flowers has been traced tosuppressionor thenon-developmentof parts,degenerationor imperfect formation,cohesionor union of parts of the same whorl,adhesionor union of the parts of different whorls,multiplicationof parts, anddeduplication(sometimes calledchorisis) or splitting of parts.

Bysuppressionor non-appearance of a part at the place where it ought to appear if the structure was normal, the symmetry or completeness of the flower is disturbed. This suppression when confined to the parts of certain verticils makes the flower asymmetrical. Thus, in many Caryophyllaceae, asPolycarponandHolosteum, while the calyx and corolla are pentamerous, there are only three or four stamens and three carpels; inImpatiens Noli-me-tangerethe calyx is composed of three parts, while the other verticils have five; in labiate flowers there are five parts of the calyx and corolla, and only four stamens; and inTropaeolum pentaphyllumthere are five sepals, two petals, eight stamens and three carpels. In all these cases the want of symmetry is traced to the suppression of certain parts. In the last-mentioned plant the normal number is five, hence it is said that there are three petals suppressed, as shown by the position of the two remaining ones; there are two rows of stamens, in each of which one is wanting; and there are two carpels suppressed. In many instances the parts which are afterwards suppressed can be seen in the early stages of growth, and occasionally some vestiges of them remain in the fully developed flower. By the suppression of the verticil of the stamens, or of the carpels, flowers becomeunisexualordiclinous, and by the suppression of one or both of the floral envelopes, monochlamydeous and achlamydeous flowers are produced. The suppression of parts of the flower may be carried so far that at last a flower consists of only one part of one whorl. In the Euphorbiaceae we have an excellent example of the gradual suppression of parts, where from an apetalous, trimerous, staminal flower we pass to one where one of the stamens is suppressed, and then to forms where two of them are wanting. We next have flowers in which the calyx is suppressed, and its place occupied by one, two or three bracts (so that the flower is, properly speaking, achlamydeous), and only one or two stamens are produced. And finally, we find flowers consisting of a single stamen with a bract. There is thus traced adegradation, as it is called, from a flower with three stamens and three divisions of the calyx, to one with a single bract and a single stamen.

Degeneration, or the transformation of parts, often gives rise either to an apparent want of symmetry or to irregularity in form. In unisexual flowers it is not uncommon to find vestiges of the undeveloped stamens in the form of filiform bodies or scales. In double flowers transformations of the stamens and pistils take place, so that they appear as petals. InCanna, what are called petals are in reality metamorphosed stamens. In the capitula of Compositae we sometimes find the florets converted into green leaves. The limb of the calyx may appear as a rim, as in some Umbelliferae; or as pappus, in Compositae andValeriana. InScrophulariathe fifth stamen appears as a scale-like body; in other Scrophulariaceae, as inPentstemon, it assumes the form of a filament, with hairs at its apex in place of an anther.

Cohesion, or the union of parts of the same whorl, andadhesion, or the growing together of parts of different whorls, are causes of change both as regards form and symmetry. Thus inCucurbitathe stamens are originally five in number, but subsequently some cohere, so that three stamens only are seen in the mature flower. Adhesion is well seen in thegynostemiumof orchids, where the stamens and stigmas adhere. In Capparidaceae the calyx and petals occupy their usual position, but the axis is prolonged in the form of a gynophore, to which the stamens are united.

Multiplication, or an increase of the number of parts, gives rise to changes. We have already alluded to the interposition of new members in a whorl. This takes place chiefly in the staminal whorl, but usually the additional parts produced form a symmetrical whorl with the others. In some instances, however, this is not the case. Thus in the horse-chestnut there is an interposition of two stamens, and thus seven stamens are formed in the flower, which is asymmetrical.

Parts of the flower are often increased by a process ofdeduplication, orchorisis,i.e.the splitting of a part so that two or more parts are formed out of what was originally one. Thus in Cruciferous plants the staminal whorl consists of four long stamens and two short ones (tetradynamous). The symmetry in the flower is evidently dimerous, and the abnormality in the androecium, where the four long stamens are opposite the posterior sepals, takes place by a splitting, at a very early stage of development, of a single outgrowth into two. Many cases of what was considered chorisis are in reality due to the development of stipules from the staminal leaf. Thus inDicentraandCorydalisthere are six stamens in two bundles; the central one of each bundle alone is perfect, the lateral ones have each only half an anther, and are really stipules formed from the staminal leaf. Branching of stamens also produces apparent want of symmetry; thus, in the so-called polyadelphous stamens of Hypericaceae there are really only five stamens which give off numerous branches, but the basal portion remaining short, the branches have the appearance of separate stamens, and the flower thus seems asymmetrical.

Cultivationhas a great effect in causing changes in the various parts of plants. Many alterations in form, size, number and adhesion of parts are due to the art of the horticulturist. The changes in the colour and forms of flowers thus produced are endless. In the dahlia the florets are rendered quilled, and are made to assume many glowing colours. In pelargonium the flowers have been rendered larger and more showy; and such isalso the case with theRanunculus, the auricula and the carnation. Some flowers, with spurred petals in their usual state, as columbine, are changed so that the spurs disappear; and others, asLinaria, in which one petal only is usually spurred, are altered so as to have all the petals spurred, and to present what are calledpelorianvarieties.

Fig. 41.—Tetramerous monochlamydeous male flower of the Nettle (Urtica).

Fig. 42.—Diagram to illustrate valvular or valvate aestivation, in which the parts are placed in a circle, without overlapping or folding.

Fig. 43.—Diagram to illustrate induplicative or induplicate aestivation, in which the parts of the verticil are slightly turned inwards at the edges.

As a convenient method of expressing the arrangement of the parts of the flower,floral formulaehave been devised. Several modes of expression are employed. The following is a very simple mode which has been proposed:—The several whorls are represented by the letters S (sepals), P (petals), St (stamens), C (carpels), and a figure marked after each indicates the number of parts in that whorl. Thus the formula S5P5St5C5means that the flower is perfect, and has pentamerous symmetry, the whorls being isomerous. Such a flower as that of Sedum (fig. 33) would be represented by the formula S5P5St5+5C5, where St5+5indicates that the staminal whorl consists of two rows of five parts each. A flower such as the male flower of the nettle (fig. 41) would be expressed S4P0St4C0. When no other mark is appended the whorls are supposed to be alternate; but if it is desired to mark the position of the whorls special symbols are employed. Thus, to express the superposition of one whorl upon another, a line is drawn between them,e.g.the symbol S5P5| St5C5is the formula of the flower of Primulaceae.

Fig. 44.—Diagram to illustrate reduplicative or reduplicate aestivation, in which the parts of the whorl are slightly turned outwards at the edges.

Fig. 45.—Diagram to illustrate contorted or twisted aestivation, in which the parts of the whorl are overlapped by each other in turn, and are twisted on their axis.

Fig. 46.—Diagram to illustrate the quincuncial aestivation, in which the parts of the flower are arranged in a spiral cycle, so that 1 and 2 are wholly external, 4 and 5 are internal, and 3 is partly external and partly overlapped by 1.

1 and 2, The alae or wings.

3, A part of the carina or keel.

4, The vexillum or standard, which, in place of being internal, as marked by the dotted line, becomes external.

5, The remaining part of the keel.

The order of the cycle is indicated by the figures.

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