Vegetable Teratology Part 19

Primulaceae. *Dodecatheon. *Cortusa.

*Anagallis! *Anagallis!

*Primula.

Dipsacaceae. Scabiosa.

Compositae. Hieracium! Hieracium!

Cirsium. Cirsium.

Hypochaeris. Calendula!

Spilanthes.

Carthamus.

Coreopsis.

Campanulaceae. Campanula. *Campanula!

Polygonaceae. Genera not specified. Rumex.

Santalaceae. Thesium.

Liliaceae. Genera not specified. Tulipa!

Hemerocallis!

Asphodelus.

Hyacinthus!

Iridaceae. Iris.

Amaryllidaceae. Narcissus!

Leucojum.

Orchidaceae. Orchis!

Habenaria.

Cyperaceae. Carex.

Gramineae. Phleum.

=Axillary prolification= is the term applied to those cases wherein one or more advent.i.tious buds spring from the axils of one or more of the parts of the flower. Engelmann makes use of the word ecblastesis to denote the same condition. Both terms are open to the objection that they do not clearly enable us to distinguish prolification occurring within the flower from a similar state originating outside the flower, within the bracts of the inflorescence. This latter condition, called by Moquin-Tandon lateral prolification (see Prolification of the Inflorescence), is as truly axillary as that to which the name is restricted. In consequence of certain peculiarities in the structure of some flowers, to be hereafter alluded to, it is not in all cases easy to decide whether the new growth springs from the interior of the flower, or from the inflorescence beneath the flower.

The accessory bud presents itself as a leaf-bud, a branch, a flower-bud, or a miniature inflorescence; it may be sessile, but is far more frequently stalked, and in more than half the number of cases it is a flower-bud or an inflorescence. There may be one or more of these buds; if two only, then they are usually placed directly opposite one to the other, on the opposite sides of the flower.

It will be seen, from the appended list, that the orders and genera in which this description of advent.i.tious growth occurs most frequently are the following:--_Cruciferae_, especially the genus _Bra.s.sica_; _Caryophyllaceae_, e.g. _Dianthus_; _Resedaceae_; _Leguminosae_, e.g.

_Melilotus_, _Trifolium_, &c.; _Rosaceae_, e.g. _Rosa_, _Potentilla_, &c.; _Umbelliferae_, and _Campanulaceae_. For the most part, these are groups also peculiarly liable to central prolification.

All the parts of the flower may be thus affected; but, as might have been antic.i.p.ated from the foliaceous nature of the sepals, the new bud usually arises from within the axil of one of those organs. Next in frequency to the calyx, the pistil is subjected to this change--the carpels in such a case being disunited and leaf-like. The petals rank next, and lastly the stamens; these latter, indeed, are usually, but not invariably, absent, the new growth occupying their position. Hence it may well be that when such is the case, there is no real axillary prolification, but rather the subst.i.tution of a bud for a stamen.

Generally, however, the position of the accessory bud is such that it may properly be referred to the axil of an undeveloped or rudimentary stamen.

The largest number of instances of this malformation, not merely generically, but also individually, occurs in plants the members of whose floral whorls are not united one to the other; thus, it is far more common in polypetalous plants than in gamopetalous ones. In the prolified flowers belonging to the latter group, the sepals, if not actually uncombined, are only united for a short distance. The same relationship, but in a much less degree, exists in the case of median prolification, as that aberration is likewise most commonly met with in polypetalous flowers. Another feature of interest is the rarity with which axillary prolification is found in irregular gamopetalous blooms.

It may be that the irregular and comparatively excessive growth in some parts of these flowers, as compared with others, may operate in checking any luxuriant tendency in other directions.

As in the case of median prolification, plants having an indefinite inflorescence are more liable to be affected with ecblastesis than those having a definite one. The degree of branching of the inflorescence may be noticed, as this deformity is far more common in plants whose peduncles are branched than in those which have either a solitary flower or an unbranched flower-stalk. More than two thirds of the entire number of genera cited as the subjects of this malformation have a branched inflorescence of some form or other; and about two thirds of the cases occur in genera having some form of indefinite inflorescence. If individual instances could be accurately computed, the proportion would be even higher.

Fully three fourths of the entire number of genera recorded as occasionally the subjects of this irregularity possess in their usual state some peculiarity of the thalamus; for instance, in about a third of the whole number of genera the thalamus is more or less prolonged between some or other of the floral whorl, e.g. _Caryophyllaceae_, _Potentilla_, _Anemone_, _Dictamnus_, _Umbelliferae_, &c. About one fourth of the genera have numerous stamens or numerous carpels, or both, springing naturally from the thalamus. In others (about one sixth) the thalamus is enlarged into a disc, or else presents one or more glandular swellings, _e.g._ _Reseda_, _Nymphaea_, _Cruciferae_. In the last-named family, as has been already remarked, prolification is very common. It would be interesting to ascertain precisely what part of an inflorescence is most liable to this affection; but as information on this point is but rarely given in the records of these cases, I can only give the results of my own observations, which go to show that, in a many-flowered inflorescence, those flowers at the outside, or at the lower portion, seem to be more frequently the subjects of this change than those situated elsewhere. This may probably be accounted for by the fact that the malformation is met with most generally in plants with an indefinite form of inflorescence, and therefore the lowermost or outermost flowers are most fully nourished; the upper flowers being in a less advanced condition, the change is more likely to be overlooked in them; or it may be that from the unusual luxuriance in the lower flowers, the upper ones may be either present in their ordinary condition, or may be (as indeed frequently happens) stunted in the size and proportion of their several parts.

=Axillary foliar prolification of the flower.=--The formation of an advent.i.tious leaf-bud in the axil of any of the parts of the flower is not of such common occurrence as the development of a flower-bud in similar situations, nor is it so frequent as median foliar prolification. I have seen leafy shoots proceeding from the axils of the sepals in the flowers of _Bra.s.sica_, and a similar occurrence has been noticed in _Caltha pal.u.s.tris_, _Herreria parviflora_, and other plants.

Dr. Marchand's flowers of _Anagallis_, previously referred to at p. 117, showed good ill.u.s.trations of this occurrence, as also some specimens described by Kirschleger in _A. phoenicea_.[134] Steinheil has figured and described[135] a flower of _Scabiosa_ in which there was an advent.i.tious formation of leafy shoots in the axil of the outer calyx.

In some flowers, such as _Convolvulus_, _Anemone_, &c., the exact nature of the sub-floral leaves is uncertain, _i.e._ it is open to doubt whether the organs in question are bracts or leaves pertaining to the inflorescence, or whether they are really parts of the flower. When leafy shoots are formed in the axils of such organs, the advent.i.tious growth may be referred to extra-floral prolification, prolification of the inflorescence that is, or to axillary prolification, according to the view taken of the real nature of the sub-floral leaves. So far as the mere occurrence of prolification is concerned, it is not very material which view be adopted. The same remark applies to cases where leaf-buds occur on the outer surface of inferior ovaries, as in _Rosaceae_, _Pomaceae_, _Philadelphus_, or _Tetragonia expansa_, as elsewhere mentioned.

It would seem more consistent with the general arrangements of parts, that the advent.i.tious buds should be formed more frequently outside than within the flower proper.

Knight[136] figures and describes the occurrence of small tubers or fleshy leaf-buds in the axils of the sepals of a potato, a curious ill.u.s.tration of the real morphological nature of the tuber.

=Axillary floral prolification of the flower.=--As already stated, this is of more common occurrence than the formation of a leaf-bud in a similar situation. Any of the parts of the flower may thus subtend a flower-bud, though probably the new buds more frequently originate in the axils of the sepals than in the other whorls. In _Cruciferae_ the change in question is, relatively speaking, very common. In cauliflowers and broccoli I have frequently met with stalked flowers proceeding from the axils of the sepals, so also in some fuchsias I have seen a ring of stalked flower-buds alternating with the petals, which, together with the stamens and pistil, remained unaffected. The number of parts in the supernumerary structures is generally less than the normal flowers.

In Mr. Herbert Spencer's 'Principles of Biology,' part iv, p. 37, are figured and described some monstrous inflorescences in _Angelica_ and other _Umbelliferae_, from which, amongst other things, the author draws the conclusion that there is no absolute distinction between leaf and branch. Without staying for the moment to discuss this matter, it may here be said that the Umbellifers in question apparently owe their peculiarities rather to axillary prolification within the flower, or to prolification of the inflorescence, than to an actual transformation of a flower or any portion of a flower into an umbellule.[137]

In the 'Gardeners' Chronicle,' 1855, p. 551, an instance is figured of the production of a supernumerary flower proceeding from the axil of a stamen in a species of _Nymphaea_ (fig. 65). The ovary in this case was wanting, but in its place was a tuft of small leaves. It is curious that among Dr. Kirk's drawings of east tropical African plants now at Kew, there should be one representing a precisely similar state of things.

The species in both instances was _Nymphaea Lotus_, or a cultivated variety of it.

M. Wesmael[138] describes a very singular case of what appears to have been referable to axillary prolification in the flowers of _Carex acuta_. The rachillus is described as prolonged through the utricle by the side of the stigmas, bearing on its side a bract, then a secondary utricle, from the axil of which sprung a short stem surmounted by an ovary. Wigand, 'Flora,' 1856, mentions a similar change in _Carex glauca_. In this instance the base of the female inflorescence bore lateral spikes, which projected from the utricles; some of these advent.i.tious spikes were female, others female below and male above, others, again, wholly male.

[Ill.u.s.tration: FIG. 65.--Flower of _Nymphaea Lotus_, var., showing axillary floral prolification. The section also shows the tuft of leaves that occupied the place of the ovary.]

Various changes in the form and arrangement of the several floral whorls accompany axillary prolification; some of these affect the particular organ or organs implicated, and these only, while in other cases some other parts of the flower likewise undergo modification. The changes most commonly met with are such as may be cla.s.sed under Goethe's theory of retrograde metamorphosis; for instance, if a supplementary bud be developed in the axil of a sepal, that sepal is likely to be more than ordinarily leaf-like in appearance. The dislocation of the affected sepal from its fellows is a very frequent occurrence; in cases of this kind the detached sepal is placed below the others, thus approximating, in position as well as in function, to the bracts. In some of the instances of proliferous pears, on which I shall have occasion to comment, the sepals are described as sharing in the succulent character of the fruit.

The petals, under such circ.u.mstances, often exist in the guise of sepals or of small leaves; and instances are recorded wherein the place of the calyx and corolla was supplied by a succession of overlapping green scales, from the axils of which the new buds arose. M. Germain de Saint Pierre records such a case in _Trifolium repens_, wherein the calyx and corolla were replaced by overlapping scales, in the axils of each one of which arose a flower; above there was a row of stamens, and in the centre a pistil in the guise of a trifoliate leaf.[139] Such instances seem to afford an extreme degree of a more common change, viz., the diminished size and contracted appearance of the sepals and petals when affected with axillary prolification. They have also a close relationship to such developments as we see in the wheat-ear carnation, in certain species of the genus _Maesa_ and others, wherein the calyx is repeated over and again, to the partial or complete suppression of the other parts of the flower. All these cases may be in part explained by the operation of the principle of compensation.

So far as the androecium is concerned, the stamens either remain unaltered, or they are present in a more or less petal-like condition; but it far more frequently happens that the stamens are entirely suppressed, the advent.i.tious bud supplying their place; thus was it in the _Dianthus_ represented in the adjoining woodcut, fig. 66, where the stamens were entirely absent, and their places supplied by flower-bearing branches. This _Dianthus_ has the more interest from its similarity to the one described by Goethe, Metam. der Pflanzen, cap.

16, sect. 105; but in that instance median prolification also existed.

For my specimens I am indebted to Mr. T. Moore.

[Ill.u.s.tration: FIG. 66.--Flower of _Dianthus_ sp., calyx removed; petals turned down so as to show the stalked flower-buds springing from their axils.]

The pistil, too, is necessarily subject to very grave alterations when affected with this malformation. It is separated into its const.i.tuent carpels; and these a.s.sume a leaf-like aspect, and are in the great majority of instances dest.i.tute of ovules. Indeed, virescence or chloranthy is very intimately connected with this aberration, as might have been antic.i.p.ated, for if the parts of the flower a.s.sume more or less of the condition of stem-leaves or bracts, it is quite natural to expect that they will partake likewise of the attributes of leaves, even at the expense of their own peculiar functions.

It occasionally happens that an advent.i.tious bud arises from the axil of a monocarpellary pistil. This takes place sometimes in _Leguminosae_, and seems to have been more frequently met with in _Trifolium repens_ than in other plants. The species named is, as is well known, particularly subject to a reversion of the outer whorls of the flower to leaves, and even to a leaf-like condition of the pistil. There are on record instances wherein a leaf-bud has been placed in the axil of a more or less leaf-like carpel; while at other times a second imperfect carpel has been met with in the axil of the first.[140] I have myself seen numerous imperfectly developed cases of this kind.

It may be asked whether such cases are not more properly referable to central prolification--whether the axis is not in such flowers terminated by two, rather than by one carpel? It is, however, generally admitted by morphologists that the solitary carpel of _Leguminosae_ is not terminal, but is the sole existing member of a whorl of carpels, all the other members of which are suppressed as a general rule, though exceptional instances of the presence of two and even of five carpels have been described.[141]

Again, the advent.i.tious bud or carpel is placed, not laterally to the primary one, or opposite to it, on the same level, but slightly higher up--in fact, in the axil of the primary carpellary leaf. Griffith figures and describes[142] an instance of the kind in a species of _Melilotus_. The stalk of the ovary is mentioned as having a sheathing base, bearing in its axil a prolongation of the axis of inflorescence, in the form of a short spike with hairy bracts and imperfect flowers, the latter having a well-formed calyx and rudimentary petals and stamens. Griffith infers, from this specimen, that the legume is not to be considered as a terminal leaf.

_List of Genera in which Axillary Prolification has been observed._

Order Genus. Leaf-bud Flower-bud or From what organ.

or Branch Inflorescence

Ranunculaceae Clematis Flower-bud Sepals.

Caltha Ditto Ditto.

Aconitum Ditto.

Delphinium Ditto Sepals, carpels, &c.

Anemone! Ditto Involucre?

Nymphaeaceae Nymphaea! Fruit?

Nymphaea Flower Petal.

Cruciferae *Bra.s.sica! Leaf-bud Flower-bud Sepals and petals.

Bra.s.sica! Ditto Stamens.

Bra.s.sica! Ditto Ditto Pistil.

Cardamine! Ditto Sepals.

Matthiola! Ditto Sepals and petals.

Cheiranthus! Ditto Sepals.

Erysimum Ditto Sepals and pistils.

Lepidium! Ditto Petals and stamens.

Arabis Ditto Sepals.