CHAPTER II.

PROLIFICATION.

Moquin-Tandon and other writers have cla.s.sed the production of buds in unwonted situations under the head of multiplication, but, as the altered arrangement is of graver import than the mere increase in number, it seems preferable to place these cases under this heading rather than under that of alterations of number.

The advent.i.tious bud may be a leaf-bud or a flower-bud; it may occupy the centre of a flower, thus terminating the axis, or it may be axillary to some or other of its component parts, or, again, it may be extra-floral. In this last case the prolification is of the inflorescence, and is hardly distinguishable from multiplication or subdivision of the common flower-stalk. In accordance with these differences we have median, axillary, and extra-floral prolification, each admitting of subdivision into a leafy or a floral variety, according to the nature of the advent.i.tious bud. Under the head of each variety certain special peculiarities are noticed, but it may here be advisable to add a few general remarks on the subject.

Axillary prolification is a much less frequent malformation than the median form. If only the number of orders and genera be reckoned, the truth of this statement will be scarcely recognised; but if individual cases could be estimated, the difference in frequency between the two would be very much more obvious. This may, perhaps, be explained by the fact that the branch has a greater tendency to grow in length than it has to develop buds from the axils of the leaves. The flower is admitted to be h.o.m.ologous with the branch, and it is also known that, up to a certain time, the branch-bud or leaf-bud and the flower-bud do not essentially differ.[104] At a later stage the difference between the two is manifested, not only in the altered form of the lateral organs in the flower-bud, but in the tendency to an arrest of growth, thus limiting the length of the central axial portion. Now, in prolified flowers the functions and, to a considerable extent, the appearance of a leaf-bud or of a branch are a.s.sumed, and with them the tendency to grow in length is developed. Median prolification, therefore, in this sense, is a further step in retrograde metamorphosis than is the axillary form. To grow in length, and to produce axillary buds, are alike attributes of the branch; but the former is much more frequently called into play than the latter; for the same reason, median prolification is more common than the axillary form. This is borne out by the frequency with which apostasis, or the separation of the floral whorls one from another, to a greater degree than usual, is met with in prolified flowers.

In both forms the advent.i.tious growth is much more frequently a flower-bud or an inflorescence than a leaf-bud or a branch. This may be due to the position of the flowers on a portion of the stem of the plant especially devoted to the formation of flower-buds, to the more or less complete exclusion of leaf-buds, _i.e._ on the inflorescence. This conjecture is borne out by the comparative rarity with which prolification has been observed in flowers that are solitary in the axils of the ordinary leaves of the plant. If the lists of genera appended hereto be perused, it will be seen that nearly all the cases occur in genera where the inflorescence is distinctly separated from the other branches of the stem. In direct proportion, then, to the degree in which one region of the axis or certain branches of a plant are devoted to the formation of flower-buds to the exclusion of leaf-buds, is the frequency with which those flowers become affected with floral prolification.

Flowers produced upon indefinite inflorescences are liable to be affected with either form of prolification more frequently than those borne upon definite inflorescences. Prolification in both varieties is also more frequently met with in branched inflorescences than in those in which the flowers are sessile; but the degree of branching seems less material, inasmuch as this malformation is more commonly recorded as occurring in racemes than in the more branched panicles, &c. From the similar arrest of growth in length, in the case of the flower, to that which occurs in the stem in the case of definite inflorescence, it might have been expected that axillary prolification would be more frequent in plants having a cymose arrangement of their flowers than in those whose inflorescence is indefinite; such, however, is not the case. The reason for this may be sought for in the lengthening of the floral axis, so common in prolified flowers--a condition the reverse of that which happens in the case of definite inflorescence.

Median prolification occurs frequently in double flowers; the axillary variety, on the other hand, is most common in flowers whose lateral organs have a.s.sumed more or less of the condition of leaves. The other coincident changes are alluded to elsewhere or do not present useful points of comparison, and may therefore be pa.s.sed over.

=Prolification of the inflorescence.=--This consists in the formation of leaf-buds or of an undue number of flower-buds on the inflorescence. It must be distinguished from virescence, or the mere green colour of the floral organs, and from chloranthy, in which all or the greater portion of the parts of the flower are replaced by leaves. Prolification is, in fact, a formation of supernumerary buds, leafy or floral, as the case may be, these buds being sessile or stalked, the ordinary buds being not necessarily changed. Prolification of the inflorescence, like the other varieties, admits of subdivision, not only according to the foliar or floral nature of the bud, but according to its position, terminal or median and lateral.

Terminal prolification of the inflorescence, whether leafy or floral, is hardly to be looked upon in the light of a malformation[105] seeing that a similar condition is so commonly met with normally, as in _Epacris_, _Metrosideros_, _Bromelia_, _Eucomis_, &c., wherein the leafy axis projects beyond the inflorescence proper; or as in _Primula imperialis_, in which plant, as also in luxuriant forms of _P. sinensis_, tier after tier of flowers are placed in succession above the primary umbel.

Nevertheless, when we meet with such conditions in plants which, under ordinary circ.u.mstances, do not manifest them, we must consider them as coming under the domain of teratology.

=Median foliar prolification of the inflorescence= is frequently met with in _Coniferae_, and has of late attracted unwonted attention from the researches of Caspary, Baillon, and others, on the morphology of these plants. The scales and bracts of the cone in these abnormal specimens frequently afford transitional forms of the greatest value in enabling morphologists to comprehend the real nature of the floral structure. It would be irrelevant here to enter into this subject; suffice it merely to say that an examination of very numerous specimens of this kind, in the common larch and in _Cryptomeria j.a.ponica_, has enabled me to verify nearly the whole of Caspary's observations. A similar prolongation of the axis occurred in some of the male catkins of _Castanea vesca_, each of which had a tuft of small leaves at their extremity. In the common marigold and in _Lotus corniculatus_ I have also seen instances of this kind. Kirschleger[106] describes a tuft of leaves as occurring on the apex of the flowering spike after the maturation of the fruit in _Plantago_, and a similar growth frequently takes place in the common wallflower, in _Antirrhinum majus_, &c. In cases where a renewal of growth in the axis of inflorescence has taken place after the ripening of the fruit, the French botanists use the term recrudescence, but the growth in question by no means always occurs after the ripening of the fruit, but frequently before. Professor Braun cites the case of a specimen of _Plantago lanceolata_, in which the spike was surmounted by a tuft of leaves and roots, as well as a still more singular instance in _Eryngium viviparum_, in which not only did particular branches terminate in rosettes of leaves provided with roots, but similar growths proceeded from the heads of flowers themselves.

Baron de Melicoq[107] gives a case in _Primula variabilis_, in which at the top of the flower-stalk, in the centre of six flowers, was placed a complete plant in miniature, having three leaves, from the axil of one of which proceeded a rudimentary flower. Mr. W. B. Jeffries also forwarded me a polyanthus (fig. 52) in which the peduncle was surmounted by a small plant, forming a crown above the ordinary flower-stalk, just as the crown of the pineapple surmounts that fruit. A similar instance was exhibited at the Scientific Committee of the Horticultural Society on July 11th, 1868, by Mr. Wilson Saunders; the species in this case was _P. cortusoides_. To Mr. R. Dean I am indebted for a similar proliferous cyclamen, which seems similar to one mentioned by Schlechtendal.[108]

This author alludes to an a.n.a.logous circ.u.mstance in the inflorescence of _Cytisus nigricans_, where, however, the change was not so great as in the preceding cases. The instances just cited all occur in plants having an indefinite form of inflorescence; but the production of a tuft of leaves or of a leafy shoot above or beyond the inflorescence is not confined to plants with this habit of growth, for Jacquin figures and describes an instance of this nature in the cymose flower-stems of a Sempervivum. "_Hi racemi_," says he, "_ultra flores produc.u.n.tur in ramos, foliosos duo bifidos qui tandem trium unciarum longitudinem adepti fuerunt_."[109]

[Ill.u.s.tration: FIG. 52.--Inflorescence of _Polyanthus_, bearing a tuft of leaves at the top of the scape intermixed with the flowers.]

=Median floral prolification of the inflorescence=, wherein a new inflorescence projects beyond the primary one, is not uncommon in plants having their flowers arranged in close heads or umbels, as in the common wild celery and other _Umbelliferae_.[110] I have also met with it in _Trifolium repens_, in the umbellate variety of the common primrose, and in the scarlet geranium. Engelmann cites it in _Tritic.u.m repens_, Roeper in _Euphorbia pal.u.s.tris_.[111]

=Lateral foliar prolification of the inflorescence= is of more common occurrence than the preceding. I have met with it, amongst other plants, frequently in _Bra.s.sica oleracea_, _Pelargonium zonale_, SCABIOSA, BELLIS, and many other composites, also in _Leguminosae_, e.g. _Lupinus_, _Trifolium_, _Coronilla_, &c. Prof. Oliver forwarded me a specimen of _Euphorbia geniculata_ in which, in addition to other changes, there was a series of stalked buds bearing tufts of green scales, but without any trace of stamens or pistil; these advent.i.tious buds occurred within the ordinary involucre of the plant, between it and the stamens. The pistil was unaffected in some cases, while in some others it was entirely wanting, the gynoph.o.r.e being surmounted by a cup-like involucre, divided into three acutely pointed lobes, each with a midrib; these encircled a series of stalked involucels, as before, and among which were scattered a few stamens, some perfect, others partially frondescent.

In a specimen of _Scrophularia nodosa_ examined by me one of the lateral buds on each of the cymes was represented, not by a flower, but by a tuft of leaves, the other buds being unchanged. As the inflorescence was much contracted in size, the appearance of the whole plant was greatly changed.

Many of the instances of so-called viviparous plants, _e.g._, _Polygonum viviparum_, may be cited under this head.[112] Many species of _Allium_, _Lilium_, _Saxifraga_, _Begonia_, _Achimenes_, normally produce leaf-buds or bulbs in the inflorescence; so, too, leafy shoots are sometimes found in _Alisma natans_, _Juncus uliginosus_, _Chlorophytum Sternbergianum_, &c. As an accidental occurrence, a similar thing has been noticed in _Lychnis coronaria_, _Phaius grandifolius_, _Oncidium cebolleta_, _Epidendrum elongatum_,[113] &c. &c.

Here, too, may be mentioned those cases wherein a leaf-bud is found upon the surface of the so-called inferior ovary; generally a leaf only is found, but a leaf-bud may also originate in this situation, and in either case the inference is that the ovary is, in part at least, made of the dilated and hollowed axis. Leaves may occasionally be found in this way on the so-called calyx-tube or on the inferior ovaries of roses, pears, apples, _Pereskia_, _Crataegus tanacetifolia_, &c.

The fruits of _Opuntia Salmania_ and of _O. fragilis_ ('Bull. Soc. Bot.

France,' vol. i, p. 306; vol. v, p. 115) have been observed to form small fruit-like branches around their summits. This circ.u.mstance is more fully treated of in the succeeding chapter relating to Heterotaxy.

=Lateral floral prolification of the inflorescence.=--This, which is termed by Engelmann Ecblastesis foliorum sub floralium,[114] is much the most common of all these deviations, and it is met with in every degree, from the presence of a single supernumerary flower in the axil of a bract to the existence of a small cl.u.s.ter or panicle of such flowers.

[Ill.u.s.tration: FIG. 53.--Lateral prolification in inflorescence of _Pelargonium_.]

It is common in the _Anemone coronaria_ and _hortensis_, also in the common scarlet _Pelargonium_ (fig. 53). It has been frequently recorded in _Poterium sanguisorba_, and in _Sanguisorba officinalis_, and is especially common in _Umbelliferae_, _Dipsacaceae_, and _Compositae_; a familiar ill.u.s.tration in the latter order is afforded by the hen-and-chicken daisy. In some species of Compositae, indeed, it is a normal and constant occurrence, while in other cases, such as _Filago germanica_, usually described as proliferous, there is not, strictly speaking, any prolification, for the branching of the stalk takes place below the inflorescence, and the branches originate from the axils of ordinary leaves, not from the floral leaves or bracts. _Convolvulus Sepium_ is very commonly subject to the production of flower-buds from the axils of the floral leaves. The several species of Plantain (_Plantago_) seem very liable to this and similar changes.

Schlechtendal[115] gives a summary of the various kinds of malformation affecting the inflorescence in _Plantago_, and divides them into five groups, as follows:--1st, bracteate, wherein the inferior bracts are quite leaf-like, as is frequently seen in _Plantago major_. 2nd, roseate; bracts leafy in tufts or rosettes, without flowers, as in the so-called rose plantain, common in old-fashioned gardens in this country. 3rd, polystachyate; spike-branched, bearing other spikes in the axils of the bracts, as in _P. lanceolata_, _P. maritima_, &c. 4th, proliferous, where the flower-stalk bears a rosette, a spike, or a head with other rosettes. 5th, paniculate, in which the inflorescence has become a much-branched pyramidal panicle, covered with little bracts, and with very rudimentary flowers.[116] The first two groups belong rather to frondescence of the bracts; but with regard to the whole of them it will easily be surmised that intermediate forms occur, linking one group to the other, and defying exact allocation in either. Thus, in the borders of richly cultivated fields in the neighbourhood of London I have frequently gathered specimens of _Plantago major_ with a branched spike provided with large leafy bracts, the branches of the spike being but little less in diameter than the ordinary single spike. These specimens would therefore seem to be intermediate between Schlechtendal's bracteate and polystachyate divisions. Wigand[117] also describes an anomalous specimen of _Plantago major_ similar to those just mentioned, but having small lateral spikes in place of large ones.

The instance quoted from Professor Braun would fall under the roseate section, as would also that of Kirschleger, though we are expressly told that the tuft of leaves in this last case was not developed until after the ripening of the seed-vessel. One of the characters of the roseate group, according to Schlechtendal, is the absence of flowers, but most persons who have had the opportunity of watching the growth of the rose plantain must have observed the occasional production of flowers, sometimes stalked, in the axils of the leafy bracts, and at the same time have noticed that the internodes become elongated, so that an approach is made to the ordinary spike-like form of the inflorescence.

The proliferous group would include such specimens as that of _P.

lanceolata_ mentioned by Dr. Johnston,[118] wherein were several spikes, some sessile, others stalked and pendent, the whole intermixed with leaves and disposed in a rose-like manner. I have myself gathered specimens of this nature, occurring in the same plant, at Shanklin, Isle of Wight (fig. 56).

[Ill.u.s.tration: FIG. 54.--_Plantago major_, with panicled inflorescence.]

[Ill.u.s.tration: FIG. 55.--Inflorescence of _Plantago major_, with bracts partly replaced by leaves and spike branched.]

[Ill.u.s.tration: FIG. 56.--Inflorescence of _Plantago lanceolata_, bearing a tuft of leaves and flowers at the end of the flower-scape.]

It is rather singular that each species of _Plantago_ seems to have its own perverse mode of growth; for instance, the bracteate, polystachyate and paniculate forms are almost exclusively confined to _P. major_, the roseate form to _P. media_, the proliferous form to _P. lanceolata_.

The instances wherein flower-buds originate from the surface of an inferior ovary, as in those cases where the top of the stem is dilated so as to form part of the fruit, would be properly cla.s.sed under the head of prolification of the inflorescence. As, however, there is still some difference of opinion as to the correct morphological interpretation to be put on some of these cases, it has been thought better to include them under the head of heterotaxy than of prolification.

[Ill.u.s.tration: FIG. 57.--Branched inflorescence of _Reseda luteola_.]

Some of the cases of prolification of the inflorescence resulting in a branching of an ordinarily simple inflorescence, as in _Reseda luteola_ (fig. 57), might equally well be placed with fission or multiplication of the axile organs. Branched spikes of this character are not so common among Orchids as might be expected. Professor Reichenbach enumerates a few instances in the Report of the International Botanical Congress of London, 1866, p. 121, and the same author gives an ill.u.s.tration in his 'Orchidographia Europoea,' tab. 150.

In Gra.s.ses, as indeed in other plants with a spicate inflorescence, this change occurs not unfrequently. The common Ray Gra.s.s (_Lolium_) is especially subject to the change in question, and among cultivated cereals, maize and wheat occasionally show this tendency to subdivision.

One variety of the latter grain is cultivated in hot countries under the name of Egyptian wheat--_Tritic.u.m vulgare_, var. _compositum_.

Prolification of the inflorescence has been most frequently observed in the following genera:

_Leafy_. _Floral_.

Ranunculaceae Ranunculus. Ranunculus!

Anemone. Anemone.

Cruciferae. *Bra.s.sica!

Caryophyllaceae. Lychnis!

Dianthus!

Geraniaceae. *Pelargonium! *Pelargonium!

Leguminosae. *Trifolium! Trifolium!

Lotus! Lotus!

Coronilla!

Cytisus. Cytisus.

Rosaceae. Poterium.

*Pyrus! *Pyrus!

*Crataegus! Crataegus!

*Rosa. Rosa!

Sanguisorba.

Philadelphaceae. Philadelphus.

Cra.s.sulaceae. Sempervivum.

Echeveria.

Cra.s.sula.

Ficoideae. ?Tetragonia.

Cactaceae. Opuntia. Opuntia.

Pereskia.

Saxifragaceae. Saxifraga!

Umbelliferae. Seseli.

*Apium!

Cnidium.