Vegetable Teratology Part 30

[228] 'El. Ter. Veg.,' p. 342.

[229] Marchand, 'Adansonia,' vol. iv, p. 127.

[230] 'Bull. Acad. Belg.,' xvii. p. 17. "Fuchsia," p. 169.

PART II.

PLEIOMORPHY.[231]

Most irregular flowers owe their irregularity to an unequal development of some of their organs as compared with that of others. When such flowers become exceptionally regular they do so either because development does not keep pace with growth, and a regular flower is thus the result of an arrest of the former process (regular peloria), or because the comparatively excessive development, which usually occurs in a few parts is, in exceptional cases manifested by all, hence the flower becomes regular from the increase in number of its irregular elements.

These latter cases, then, are due to an excess of development, hence the application of the term pleiomorphy. It must be understood that mere increase in the number of the organs of a flower is not included under this head, but under that of deviations from the ordinary number of parts.

FOOTNOTES:

[231] [Greek: Pleios-morphosis].

CHAPTER I.

IRREGULAR PELORIA.

The term peloria was originally given by Linne to a malformation of _Linaria vulgaris_, with five spurs and five stamens, which was first found in 1742 near Upsal. This was considered so marvellous a circ.u.mstance that the term peloria, from the Greek [Greek: pelor], a prodigy, was applied to it.[232] After a time other irregular flowers were found in like condition, and so the term peloria became applied to all cases wherein, on a plant habitually producing irregular flowers, regular ones were formed. The fact that this regularity might arise from two totally different causes was overlooked, or at least not fully recognised, even by Moquin-Tandon himself. Where a flower retains throughout life the same relative size in its parts that it had when those parts first originated the result is, of course, a regular flower, as happens in violets and other plants. This kind of peloria may for distinction sake be called regular or congenital peloria (see chapter on that subject); but where a flower becomes regular by the increase in number of its irregular portions, as in the _Linaria_ already alluded to, where not only one petal is spurred, but all five of them are furnished with such appendages, and which are the result of an irregular development of those organs, the peloria is evidently not congenital, but occurs at a more or less advanced stage of development. To this latter form of peloria it is proposed to give the distinctive epithet of irregular.

Peloria is either complete or incomplete; it is complete when the flower appears perfectly symmetrical, it is incomplete when only a portion of the flower is thus rendered regular. It is very common, for instance, to find violets or Linarias with two or three spurs, and these intermediate stages are very interesting, as they serve to show in what way the irregularity is brought about. In _Antirrhinum_, _Linaria_, &c., intermediate forms show very clearly that it is to the repet.i.tion of the form usually a.s.sumed by the petals of the lower lip that the condition is due. This is also obvious in peloric flowers of the _Calceolaria_.

The perfect peloria of this flower is in general erect, with five regular sepals, a regular corolla contracted at the base and at the apex, but distended in the centre so as to resemble a lady's sleeve, tight at the shoulder and wrist, and puffed in the centre!

[Ill.u.s.tration: FIG. 122.--Peloric flower of _Calceolaria_.]

Morren[233] describes a form intermediate between the ordinary slipper-shaped corolla and the perfect peloria just described, and which he calls sigmoid peloria. This flower is intermediate in direction between the erect peloria and the ordinary reflected flower. The tube is curved like a swan's neck and is dilated in front into two hollow bosses, such as we see in the lower lip of an ordinary flower; beyond these it is contracted and is prolonged into a slender beak terminating in two hollow teeth, between which is the narrow orifice of the corolla. The colour at the base of the tube inside is as in the perfect peloria; while round the summit of the tube, in both cases, the intensity of colour is greatest on the outside. Now, in a normal flower the deepest colour is within just opposite the orifice of the corolla; this deep colour is also seen outside of the central and most elevated portions of the lower lip. In the peloria the deep colour at the base of the tube represents that which is near the orifice under ordinary circ.u.mstances, while the outer patch of colour at the apex corresponds to that formed on the upper surface of the lower lip. On the other hand, in peloric flowers of _Cytisus Laburnum_, _c.l.i.toria Ternatea_, _Trifolium repens_, and other Papilionaceae, it is the "standard," the form of which is repeated. In the case of peloric aconites[234] the lateral and sometimes the inferior coloured sepals a.s.sume the hooded form usually peculiar to the upper sepal only, the number of the petals or nectaries being correspondingly increased. Balsams become peloric by the augmentation in the number of spurs.[235] So when orchids are affected with irregular peloria it is the form of the labellum that is repeated, the accessory lips being sometimes the representatives of stamens, which are usually suppressed in these flowers,[236] but at other times the appearance is due simply to the fact that all three petals a.s.sume the form usually confined to the lip, the staminal column being unaffected, except that its direction and relative position with reference to the other parts of the flower is different from ordinary.

This was the case in some flowers of _Phalaenopsis equestris_ sent to me by Mr. Wentworth Buller. Fig. 123 represents a flower of _Aristolochia caudata_ with two lips, for which I am indebted to Mr. W. H. Baxter.

From these cases it is evident that the flowers in question become regular by the repet.i.tion of the irregular parts.

[Ill.u.s.tration: FIG. 123.--Two-lipped flower of _Aristolochia caudata_.]

It is probable that peloria may occur in any habitually irregular flower, and that, if more attention were directed to the subject, ill.u.s.trations might be obtained from a larger number of natural families than can be done at present. It is, however, necessary to exercise discrimination, and not to attribute to peloria all the cases that at first sight appear to be so referable. Thus, Professor d.i.c.kson exhibited at the Botanical Society of Edinburgh, December 13th, 1860, four abnormal flowers of the common Indian cress (_Tropaeolum majus_), each presenting a supernumerary spur. On these he remarked that "in _Tropaeolum_ the posterior part of the receptacle between the insertion of the petals and that of the stamens is dilated so as to form the spur which is so characteristic in the genus. The position of the spur in a line with the posterior sepal has led many botanists to consider it as a process of that sepal, but the fact of its being situated within the insertion of the petals is conclusive as to its receptacular origin. In the flowers exhibited the supernumerary spur (as if to show its want of connection with any sepal) was placed exactly between a lateral sepal and one of the anterior sepals, sometimes on the one side of the flower and sometimes on the other. These additional spurs were precisely similar to the normal ones, except that they were a little shorter. This abnormality, although at first sight seeming to indicate a pelorian tendency, is no approximation to regularity, from the fact of the extra spur being differently placed, with regard to the sepals, from the normal one."

Peloria of this kind, when perfect, is very often a.s.sociated with other alterations. Change of direction is one of the most common of these; the usually drooping flower becomes erect, the stamens and style also are changed in direction, while, not unfrequently, either the one or the other (most often the stamens) are entirely suppressed. With this suppression an increase in the size of the flower very generally coincides. The number of parts is also frequently increased; thus, in _Antirrhinum majus_ the corolla, when subjected to peloria, is very generally six-parted, and has six stamens. Fusion of one or more flowers is also a common accompaniment of peloria, as in _Digitalis purpurea_, in which plant prolification often adds increased complexity to the flower.

It has been stated by Moquin and others that the uppermost flower of an inflorescence is the most subject to peloria; the uppermost flower of _Teucrium campanulatum_, for instance, is very generally regular. In _Calceolaria_ it is the central terminal flower which is usually peloriated; on the other hand, in _Linaria_ and _Antirrhinum_ the lower flowers, or those on the secondary branches, are quite as often affected as the primary ones. Ca.s.sini considered that the spur of _Linaria_ was developed from the lower petal rather than from the upper ones, because there is more room on the side of the flower farthest from the stem than on the opposite side. With reference to this point, M. G.o.dron remarks that in habitually irregular flowers the apex of the peduncle is oblique, and hence the flowers are bent downwards or spread horizontally, but if the receptacle be quite flat and level then the flower is regular. The oblique position causes some of the organs to press on others, and hence induces abortion and suppression of some parts and increased growth in others that are not subjected to pressure.

In a terminal peloriated flower of aconite, described by this naturalist, the flower was removed so far from the nearest bracts that all its parts had the chance of growing regularly. In ordinary cases M.

G.o.dron considers that the compression of the lateral bracts is the cause of the irregularity of the androecium and of the receptacle.[237]

It has also been somewhat too generally stated that peloria occurs princ.i.p.ally on luxuriant vigorous plants. It seems quite as often to happen in plants characterised by their deficiencies in this respect. On this point M. de Melicoq[238] says, referring to _Linaria vulgaris_ affected with peloria, that on the weakest plants the peloriated flower was at the top of the stem; while in stronger plants, with more numerous flowers and larger foliage, the peloriated flowers were princ.i.p.ally to be found in the centre and at the base of the inflorescence, and their pedicels were much longer than usual.

Linne, as has been already stated, considered these flowers to be sterile, and only capable of multiplication by division of the root, but Willdenow obtained seeds from the _Linaria_ which reproduced the anomaly when sown in rich soil. Baron Melicoq obtained similar results.[239] Mr. Darwin[240] raised sixteen seedling plants of a peloric _Antirrhinum_, artificially fertilised by its own pollen, all of which were as perfectly peloric as the parent plant. On the other hand, the same observer alludes to the tendency that these peloric plants have to revert to the usual form, as shown by the fact that when the peloric flowers were crossed with pollen from flowers of the ordinary shape, and _vice versa_, not one of the seedlings, in either case, bore peloric flowers. Hence, says Mr. Darwin, there is in these flowers "a strong latent tendency to become peloric, and there is also a still greater tendency in all peloric plants to reacquire their normal irregular structure." So that there are two opposed latent tendencies in the same plant. A similar remark has been made with reference to malformations in general by other observers.

It would be very interesting if some competent naturalist would collect information as to whether any variations in degree of fertility exist in the three forms of flowers in _Linaria_, viz. the ordinary one-spurred form, which is intermediate between the spur-less and the five-spurred form. It must be remembered, however, that in the latter cases the stamens are often deficient. In the _Compositae_, where there are regular flowers in the disc and irregular ones in the ray, s.e.xual differences, as is well known, accompany the diversities in form.

To Mr. Darwin the author is indebted for the communication of some flowers of _Corydalis tuberosa_ (figs. 124, 125), provided with two spurs of nearly equal size. To these flowers allusion is made in the work already quoted[241] in the following terms:--"_Corydalis tuberosa_ properly has one of its two nectaries colourless, dest.i.tute of nectar, only half the size of the other, and therefore to a certain extent in a rudimentary state; the pistil is curved towards the perfect nectary, and the hood formed of the inner petals slips off the pistil and stamens in one direction alone, so that when a bee sucks the perfect nectary the stigma and stamens are exposed and rubbed against the insect's body. In several closely allied genera, as in _Dielytra_, there are two perfect nectaries; the pistil is straight, and the hood slips off on either side, according as the bee sucks either nectary." In the flowers of _Corydalis_, which were provided with two perfect nectaries containing nectar, Mr. Darwin considers that there has been a redevelopment of a partially aborted organ, accompanied by a change in the direction of the pistil, which becomes straight, while the hood formed by the petals slips off in either direction, "so that these flowers have acquired the perfect structure, so well adapted for insect agency, of _Dielytra_ and its allies."

[Ill.u.s.tration: FIG. 124.--Two-spurred flowers of _Corydalis_.]

[Ill.u.s.tration: FIG. 125.--Section through two-spurred flowers of _Corydalis_, Magnified.]

Peloria, then, is especially interesting physiologically as well as morphologically; it is also of value in a systematic point of view, as showing how closely the deviations from the ordinary form of one plant represent the ordinary condition of another; thus, the peloric Calceolarias resemble the flowers of _Fabiana_, and De Candolle,[242]

comparing the peloric flowers of _Scrophulariaceae_ with those of _Solanaceae_, concluded that the former natural order was only an habitual alteration from the type of the latter. Peloric flowers of _Papilionaceae_ in this way are indistinguishable from those of _Rosaceae_. In like manner we may trace an a.n.a.logy between the normal one-spurred _Delphinium_ and the five-spurred columbine (_Aquilegia_), an a.n.a.logy strengthened by such a case as that of the five-spurred flower of _Delphinium elatum_ described by G.o.dron.[243] The _Corydalis_, before referred to, is another ill.u.s.tration of the same fact, the structure being the same as in _Dielytra_, &c.

The ordinary irregular flowers may possibly be degenerated descendants of a more completely organized ancestor, and some of the cases of peloria may therefore be instances of reversion; some ancient _Linaria_ may, perhaps, have had all its petals spur-shaped, and the cases of irregular peloria now found may be reversions to that original form.

When both regular and irregular forms of peloria occur on the same plant, as they frequently do in _Linaria_, the one may be perhaps considered as a reversion to a very early condition, the other to a later state, when all the petals were irregularly formed. But before we can a.s.sert the truth of this surmise we must have better evidence as to what the original condition really was than we have at present.

The proximate cause of irregular peloria has been considered to be excess of nourishment, but evidence as to this point is very conflicting. Willdenow states that "radices peloriae, solo sterili plantatae, degenerant in Linariam," ('Sp. Plant.,' iii, p. 254); but this opinion is counterbalanced by that of others, while the frequent existence of both forms on the same plant, at the same time, seems to negative the supposition of any direct effect from external circ.u.mstances.

The following are the plants in which irregular peloria has been most often observed:

Aconitum Napellus.

Delphinium elatum!

Corydalis tuberosa.

*Viola odorata!

hirta.

Impatiens Balsamina.

c.l.i.toria Ternatea.

Cytisus Laburnum!

Trifolium repens!

Lupinus polyphyllus!

*Gloxinia, var. cult.!

*Linaria vulgaris!

spuria.

Elatine.

triphylla.

aeruginea.

triornithophora.

pilosa.

chalepensis.

cymbalaria!

purpurea!

dec.u.mbens.

Pelisseriana.

origanifolia.

Digitalis orientalis.

* purpurea!

Calceolaria crenatiflora.