=Median leafy prolification.=--In this malformation the centre of the flower is occupied by a bud or a branch; the growing point or termination of the axis which ordinarily ceases to grow after the formation of the carpels, takes on new growth. This is well shown in the accompanying ill.u.s.tration (fig. 58), representing the thalamus of a strawberry prolonged beyond the fruits into a small leaf-bearing branch.

[Ill.u.s.tration: FIG. 58.--Receptacle of strawberry prolonged into a leafy branch. From the 'American Agriculturist.']

[Ill.u.s.tration: FIG. 59.--Flower of _Verbasc.u.m_ with five disunited sepals, five similar green petals, and a prolonged branch in the centre of the flower.]

In other cases the carpels are entirely absent and their place is supplied by a leafy shoot as in a species of _Verbasc.u.m_, which came under my own observation. In this case the petals were virescent, and the stamens and pistils were entirely absent, hence in truth, the so-called flower more nearly resembled a branch. In a flower of a May Duke cherry, for which I am indebted to Mr. Salter, there was a gradual change from the floral to the foliar condition; thus there were five distinct lanceolate sepals, the arrangement of whose veins betokened that they were leaf-sheaths rather than perfect leaves, ten petals partly foliaceous and sheath-like as to their venation, one of them funnel-shaped, but whether from dilatation or cohesion of the margins could not be determined. The stamens were eight or ten in number, their connectives prolonged into foliaceous or petaloid appendages, so that the filament represented the stalk of the leaf. The pistil was entirely absent and its place was supplied by a branch with numerous perfectly formed stipulate leaves.

Some flowers of _Anagallis arvensis_ described by Dr. Marchand[119] are so interesting and show so well the gradual stages by which this malformation is arrived at, that it is desirable to cite the summary of Dr. Marchand's researches as given in the 'Gardeners' Chronicle' by Mr.

Berkeley, taking that instance first in which the parts of the flower departed least from the normal condition, and then the others in their proper order. In all the parts there was a greater or less tendency to a.s.sume a green tint; in some they were entirely green, in others the brighter colours were confined to the more recently developed parts.

"1. In the first case then, the sepals and petals were in their normal position, though rather more dilated than usual; the anthers were fertile, the princ.i.p.al change existing in the ovary, the upper part of which was wanting, so that the ovules were exposed seated on the central placenta.

2. In the next step the calyx, more developed than usual, was separated from the corolla by a long peduncle, and the ovary, which was ovate, contained instead of a placenta a sort of plumule or young shoot.

3. In this case the corolla and calyx were distant from each other; there was no trace of stamens, but the axis was continued from the centre of the corolla, and ended in a leaf-bud.

4. The calyx and corolla nearly as before, but instead of stamens a whorl of little leaves was developed, in the centre of which the axis was continued, bearing at its tip two whorls of leaflets, alternately three and three.

5. In this case two out of the five stamens were normal, the other three changed into leaves, showing clearly the origin of the leaflets, in the last case, which took the place of the stamens.

6. The ovary varied in different flowers. In some the placenta was crowned with ovules; in others the ovules were replaced by a single whorl of leaflets; in others there was every shade of change from ordinary ovules to perfect leaflets; while in others, again, every ovule was converted into a leaf with a long petiole.

7. In these flowers shoots were developed in the axils of the sepals, or on the face of the petals between the point of their insertion and that of the stamens, and, what is most curious, in the interior of the ovaries round the foot of the placenta.

8. Here, again, a very singular condition presented itself: the calyx and corolla separated from each other, the stamens partly developed, the axis continued beyond the corolla, branched and bearing normal leaves so as exactly to resemble an ordinary stem, while in consequence of the calyx and corolla being bent down to the ground, advent.i.tious roots were developed from the axis on the under side above each of them. In another case, where the calyx and corolla were approximated, the ovary was open above, and sent out six shoots from within, perfectly developed, clearly representing the central placenta and five axile buds, and each giving out a number of advent.i.tious roots at its base."

In other genera of the same order (_Primulaceae_) an extension of the placenta into a leafy branch has been observed, as in _Lysimachia_, where in one case the prolonged placenta was removed and struck as a cutting.[120]

In _Ericaceae_ too, the axile placenta has been seen ovuliferous at the base and prolonged above into a leafy branch.[121]

=Median floral prolification.=--This is of more frequent occurrence than the preceding. The prolonged axis is more frequently terminated by a flower-bud than by a leaf-bud, though it must be remarked, that the lengthened and protruded stem frequently bears leaves upon its sides, even if it terminate in a flower, and thus the new growth partakes of a mixed leafy and floral nature. Instances of this kind have long been familiar to observers, and have always excited attention from the singularity of their appearance. In one of the old stained-gla.s.s windows, apparently of Dutch manufacture, in the Bodleian Picture Gallery at Oxford, is a representation of a _Ranunculus_ affected with median floral prolification.[122] In pinks the affection is not unfrequently met with. Fig. 60 shows an instance of the kind copied from Schotterbec.

A singular instance of prolification in the central flower of one of the verticillasters of _Phlomis fruticosa_ fell under my own notice; it was a case wherein the calyx was torn on one side, and one of its lobes had become petaloid. Between the calyx and the corolla were three or four spathulate, hairy, bract-like organs; the corolla and stamens were unchanged; but in place of the usual four-lobed ovary there was a single carpel with a basilar style, terminated by a forked stigma. Occupying the place of the other lobes of the pistil was an oblong woolly flower-bud, consisting of calyx, corolla, and stamens, but with no trace of pistil. I have been unable to find recorded any instance of malformation among l.a.b.i.ates or Borages at all similar to this. It differed from most other examples of prolification in that the axis was not prolonged, the advent.i.tious bud occupying precisely the position of the three lobes of the ovary that were absent. The sole remaining carpel had a style and a stigma as perfect in appearance as though the pistil had been complete.

[Ill.u.s.tration: FIG. 60.--Flower of _Dianthus_ affected with median floral prolification.]

In a flower of _Conostephium_ (_Epacridaceae_) forwarded to me by Mr.

Bentham, there was a similar advent.i.tious bud placed by the side of the pistil, but as the latter contained the usual number of cells it is probable that the supernumerary bud in this case originated rather from the side than the end of the axis.

Certain families of plants present this deviation from their ordinary structure with greater frequency than others: the following orders seem to be the most frequently affected by it: _Ranunculaceae_, _Caryophyllaceae_, _Rosaceae_; while it is commonly met with in _Scrophulariaceae_, _Primulaceae_ and _Umbelliferae_. Of genera which seem peculiarly liable to it may be mentioned the following: _Anemone_, _Ranunculus_, _Cheiranthus_, _Dianthus_, _Dictamnus_, _Daucus_, _Rosa_, _Geum_, _Pyrus_, _Trifolium_, _Antirrhinum_, _Digitalis_, _Primula_.

A reference to the subjoined list of genera affected by this malformation, and the knowledge of its comparatively greater frequency in some than in others of them, will show that it is more often met with in plants having an indefinite form of inflorescence than in those having a definite one. The change may affect some only, or the whole of the flowers const.i.tuting an inflorescence; and though it is by no means a constant occurrence, it very frequently happens that the central or terminal flower in a definite inflorescence is alone affected, the others remaining in their ordinary condition, as in pinks (_Dianthus_); and in the indefinite forms of inflorescence, it is equally common that the uppermost flower or flowers are the most liable to be thus affected.

In those plants which present this deviation from the ordinary condition with the greatest frequency, it often happens that the axis is normally more or less prolonged, either between the various whorls of the flower, as in the case of the gynoph.o.r.e, &c., or into the cavity of the carpels, as in the instances of free central placentation. To bear out this a.s.sertion, the following instances taken from those genera having definite inflorescence, and which are very commonly affected with prolification, may be cited; thus, in _Anemone_ and _Ranunculus_ the thalamus is prolonged to bear the numerous carpels; in _Dianthus_ there is a marked internode separating the carpels from the other parts of the flower; in _Primulaceae_ central prolification is very common, and this is one of the orders where the placenta seems from the researches of Duchartre and others, to be truly a production of the axis within the carpels;[123] in _Thesium_ also, another genus with free central placenta, this malformation has been found.

So also among plants with indefinite inflorescence, prolification seems very frequently to affect those wherein the axis is normally prolonged; thus it is common in _Dictamnus_, which plant has an internode supporting the pistil; it is frequent among _Umbelliferae_, where the carpoph.o.r.e may be truly considered an axile production; it is common among _Rosaceae_ and _Ranunculaceae_, in many of which the axis or thalamus is well-marked, and it is by no means infrequent in the flowers of the Orange, where the floral internodes are also slightly elongated; on the other hand, there is no case on record in _Magnoliaceae_, and some other orders where the floral part of the axis is at some point or other elongated; still, on the whole, there can be but little doubt that there is a real relation between prolification and the normal extension of the floral internodes.

Under these circ.u.mstances, those instances wherein the parts of the flower become separated one from the other by the elongation of the internodes (apostatis), const.i.tute a lesser degree of the same change, which operates most completely in the formation of a new bud at the extremity of the prolonged axis. Some specimens of _Geum rivale_ (a plant very liable to become prolified) in my possession show this very clearly. In the wild plant the thalamus is elevated on a short stalk; in the abnormal ones the thalamus is simply upon a longer stalk than usual, or in a more advanced stage of the deviation the lengthened thalamus takes the form of a branch provided with leaves and terminated by a flower; it is noticeable, also, in these specimens, that the sepals of the lower flower have a.s.sumed entirely the dimensions and appearance of leaves.

Median prolification has occasionally been recorded in flowers that have, in their ordinary condition, but one carpel, as in _Leguminosae_ and in _Santalaceae_. In _Leguminosae_, as also in _Amygdalus_, it would seem as if the advent.i.tious bud were strictly a lateral and axillary production, and moreover that the carpel itself is not strictly terminal but lateral in position, though apparently terminal from the abortion of other carpels. In the only recorded instance that I am aware of, of this malformation affecting the genus _Thesium_, the pistil was altogether absent, and occupying its place was the new bud or branch.[124]

[Ill.u.s.tration: FIG. 61.--_Daucus Carota_, showing leafly carpels, prolification, &c.]

As the carpels are not unfrequently absent in cases of median prolification, it has been thought that the pistil in such cases was metamorphosed into a stem bearing leaves or flowers. Setting aside the physiological difficulties in the way of accepting such an opinion, an examination of any number of cases is sufficient to refute it; for, as Moquin well remarks, the carpels may frequently be found either in an unaltered condition or more or less modified.

If the pistil be normally syncarpous, its const.i.tuent carpels, if present at all in the prolified flower, become disjoined one from the other to allow of the pa.s.sage between them of the prolonged axis; thus in some malformed flowers of _Daucus Carota_ gathered in Switzerland (fig. 61), not only was the calyx partially detached from the pistil, but the carpels themselves were leaf-like, disjoined, and unprovided with ovules; between them rose a central prolongation of the axis, which almost immediately divided into two branches, each terminated by a small umbel of perfect flowers, surrounded by minute bracts.[125]

Not only are the carpels thus frequently separated one from the other by the prolonged axis, but they undergo commonly a still further change in becoming more or less completely foliaceous, as in the _Daucus_ just mentioned, where the carpels were prolonged into two lance-shaped leaves, whose margins in some cases were slightly incurved at the apex, forcibly calling to mind the long "beaks" that some Umbelliferous genera have terminating their fruits--for instance, _Scandix_. Dr. Norman, in the fourth series of the 'Annales des Sciences,' vol. ix, has described a prolification of the flower of _Anchusa ochroleuca_, in which the pistil consisted of two leaves, situated antero-posteriorly on a long internode, with a small terminal flower-bud between them; and numerous similar instances might be cited.

In this place may also be noticed those instances wherein the placenta elongates so much that the pericarp becomes ruptured to allow of the protrusion of the placenta, although this prolongation is not attended by the formation of new buds. Cases of this kind occurring in _Melastoma_ and _Solanum_ have been put on record by M. Alph. de Candolle.[126] This is a change a.n.a.logous with that which occurs in some species of _Leontice_ or _Caulophyllum_, as commented on by Robert Brown. See 'Miscellaneous Botanical Works' of this author, Ray Society, vol. i, p. 359.

If the pistil be apocarpous, and the carpels arranged spirally on an elevated thalamus, it then frequently happens that the carpels, especially the upper ones, become carried up with the prolonged axis, more widely separated one from the other than below, and particularly liable to undergo various petalloid or foliaceous changes as in proliferous _Roses_, _Potentilla_, &c.

[Ill.u.s.tration: FIG. 62.--Median floral prolification, &c., in flower of _Delphinium_.]

Fig. 62, copied from Cramer, shows an instance of this kind in _Delphinium elatum_, where not only is the thalamus prolonged, and the carpels separated, but from the axils of some of the latter which have a.s.sumed from the disunion of their margins somewhat of the appearance of leaves, other flowering branches proceed--axillary prolification. If, on the other hand, the carpels be few in number, and placed in a verticillate manner, the axis then generally pa.s.ses upwards without any change in the form or position of the carpels being apparent, as in a proliferous columbine, figured in the 'Linnean Transactions,' vol.

xxiii, tab. 34, fig. 5.

When a flower with the ovary naturally inferior or adherent to the calyx becomes prolified, a change in the relative position of the calyx and ovary almost necessarily takes place, the latter becoming superior or detached from the calyx; this has been already alluded to in _Umbelliferae_. In a species of _Campanula_ examined by me, the calyx was free, the corolla double, the stamens with petaloid filaments, and in the place of the pistil there was a bud consisting of several series of green bracts, arranged in threes, and enclosing quite in the centre three carpellary leaves detached from one another and the other parts of the flower, and open along their margins, where the ovules were placed.

In other similar instances in the same species of _Campanula_, the styles were present, forming below an imperfect tube which surrounded the advent.i.tious bud; in another, contrary to what occurs usually in such cases, the ovary was present in its usual position, but surmounted by a bud of leafy scales, enclosed within the base of a tube formed by the union of the styles. A similar relative change in the position of the calyx and the ovary takes place when the _Compositae_ are affected with central prolification, or even in that lesser degree of change which merely consists in the separation and disunion of the parts of the flower, but which in these flowers appear to be, as it were, the first stage towards prolification. I owe to the kindness of Professor Oliver a sketch of a species of _Rudbeckia_? showing this detachment of the calyx from the ovary. In a monstrous _Fuchsia_ that I have had the opportunity of recently examining, the calyx was similarly detached from the ovary simultaneously with the extension of the axis. Here the petals were increased in number and variously modified, the stamens also; while in the centre and at the top of the flower, conjoined at the base with some imperfect stamens, was a carpel open along its ovuliferous margins. Such instances as these seem to be the first stages of a change which, carried out more perfectly, would result in the formation of a new bud on the extremity of the prolonged axis.

In _Orchidaceae_, among which family I have now met with several instances of prolification, the ovary seems usually to be absent. Fig.

63 shows a prolified flower of _Orchis pyramidalis_ in which the perianth was nearly regular, the central portions of the flower absent, and their place supplied by a new miniature raceme. This specimen was forwarded to me by Dr. Moore, of Glasnevin.

[Ill.u.s.tration: FIG. 63.--Median prolification in _Orchis pyramidalis_, the outer segments of the perianth regular and reflexed.]

As might be expected, it very rarely happens that median prolification occurs without some other deviation in one or more parts of the flower being simultaneously manifested. Some of these changes have been already mentioned, but others are commonly met with, as, for instance, the multiplication or doubling, as it is termed, of the petals; others, though less frequent, are of more interest. Fusion of two or more flowers in a.s.sociation with prolification is especially common in cultivated specimens of _Digitalis purpurea_; the uppermost flowers of the raceme become fused together so as to form one large, regular, erect, cup-shaped corolla, to the tube of which the stamens are attached, in greater number than ordinary, and all of equal length; the bracts and sepals are confusedly arranged on the exterior of the flower; while in the centre, in the place usually occupied by the pistil, there rises a conical prolongation of the axis, bearing at its outer or lower portion a number of open carpels, provided, it may be, with styles and ovules; these enclose an inner series of scale-like bracts, from whose axils proceed more or less perfect florets; so that in the most highly developed stage a perfect raceme of flowers may be seen to spring from the centre of a cup-shaped regular flower, whose lobes show its compound character. All intermediate stages of this malformation may be found from cases where there is a simple fusion of two flowers with a second verticil of carpels within the outer, up to such cases as those which have been just mentioned. It is worthy of special remark, that in all these cases the flowers at the uppermost part of the raceme are alone affected, and that, in addition to the prolification, there is fusion of two or more flowers, and regularity in the form of the compound corolla and stamens.

The calyx of a prolified flower is either unchanged, or it is modified in harmony with the changes in the central part of the flower. If the ovary be normally superior or free from the calyx, then the latter is comparatively rarely altered; for instance, in proliferous pinks (_Dianthus_) the calyx is seldom affected, except, indeed, in those instances where the floral axis is prolonged, and produces from its side a successive series of sepals, as in what is called the wheat-ear carnation; but though these instances may be, as I believe, an imperfect degree of prolification, they do not affect the general truth of the above opinion, that the calyx, if it be free from the ovary, is but rarely changed in a prolified flower; but that this is not a universal rule is shown by proliferous flowers of _Geum rivale_, where the sepals are usually large and leaf-like, as they likewise are frequently in proliferous roses and pears.

[Ill.u.s.tration: FIG. 64.--Proliferous rose. Hip absent, sepals leafy, stamens wanting, axis prolonged bearing supplementary flower, &c. (Bell Salter).]

Proliferous roses have a special interest, inasmuch as they show very conclusively that the so-called calyx-tube of these plants is merely a concave and inverted thalamus, which, in prolified specimens, becomes elongated (fig. 64) after the fashion of _Geum rivale_, &c.[127]

Occasionally from the middle of the outer surface of the urn-shaped thalamus proceeds a perfect leaf, which could hardly be produced from the united sepals or calyx-tube; a similar occurrence in a pear is figured in Keith's 'Physiological Botany,' plate ix, fig. 12.

The change which the calyx undergoes when flowers with an habitually adherent ovary become prolified, and wherein the calyx is disjoined from the ovary, has been before mentioned, but it may also be stated that, under such circ.u.mstances, the const.i.tuent sepals are frequently separated one from the other, and not rarely a.s.sume more or less of the appearance of leaves, as in proliferous flowers of _Umbelliferae_, _Campanulaceae_, _Compositae_, &c.

As to the corolla, it was long since noticed that prolification was especially liable to occur in double flowers; indeed, Dr. Hill, who published a treatise on this subject, setting forth the method of artificially producing prolified flowers, deemed the doubling to be an almost necessary precursor of prolification;[128] but, though frequently so, it is not invariably the case that the flower so affected is double--_e.g._ _Geum_. If double, the doubling may arise from actual multiplication of the petals, or from the subst.i.tution of petals for stamens and pistils, according to the particular plant affected.

Occasionally in prolified flowers the parts of the corolla, like those of the calyx, become foliaceous, and in the case of proliferous pears fleshy and succulent. There is in cultivation a kind of _Cheiranthus_?

in which there is a constant repet.i.tion of the calyx and corolla, conjoined with an entire absence of the stamens and pistils; a short internode separates each flower from the one above it, and thus frequently ten or a dozen of these imperfect flowers may be seen on the end of a flower-stalk, giving an appearance as if they were strung like beads, at regular intervals, on a common stalk. I have seen a similar instance in a less degree in a species of _Helianthemum_.

The stamens are subject to various changes in prolified flowers; they a.s.sume, for instance, a leaf-like or petal-like condition, or take on them more or less of a carpellary form, or they may be entirely absent; but none of these changes seem to be at all necessarily connected with the proliferous state of the flower. Of more interest is the alteration in the position of these organs which sometimes necessarily accrues from the elongation of the axis and the disjunction of the calyx; thus, in proliferous roses the stamens become strictly hypogynous, instead of remaining perigynous. In _Umbelliferae_ the epigynous condition is changed for the perigynous, &c.

The condition of the pistillary organs in prolified flowers has already been alluded to. Hitherto those instances have been considered in which either the carpels were absent, or the new bud proceeded from between the carpels. There is also an interesting cla.s.s of cases where the prolification is strictly intra-carpellary; the axis is so slightly prolonged that it does not protrude beyond the carpels, does not separate them in any way, but is wholly enclosed within their cavity.

Doubtless, in many cases, this is merely a less perfect development of that change in which the axis protrudes beyond the carpels. This intra-carpellary prolification occurs most frequently in plants having a free central placenta, though it is not confined to them, as it is recorded among _Boragineae_. A remarkable instance of this is described by Mr. H. C. Watson in the first volume of Henfrey's 'Botanical Gazette,' p. 88. In this specimen a raceme of small flowers was included within the enlarged pericarp of a species of _Anchusa_. But the most curious instances of this form of prolification are, no doubt, those which are met with among _Primulaceae_ and other orders with free central placentation.

Duchartre, in his memoir on the organogeny of plants with a free central placenta, in the 'Ann. des Sc. Nat.,' 3 ser., 1844, p. 290, among other similar instances, mentions two flowers of _Cortusa Matthioli_, wherein the placenta was ovuliferous at the base; but the upper portion, instead of simply elongating itself into a sterile cone, had produced a little flower with its parts slightly different from those of the normal flowers. M. Alph. de Candolle has likewise described somewhat similar deviations, and one in particular in _Primula Auricula_, where the elongated placenta gave off long and dilated funiculi bearing ovules, while other funiculi were dest.i.tute of these bodies, but were much dilated and foliaceous in appearance.[129] In some flowers of _Rhododendron_ I have observed a similar condition of the ovules, which, moreover, in the primary flowers, were attached to the walls of the carpels--parietal placentation.