Vegetable Teratology Part 14

In a specimen of _Lycaste Skinneri_ similar changes were observed, as shown in the plan, fig. 47. Here the posterior sepal was deficient, the two lateral ones were present, one of them with a long tubular spur, _o o_; of the two lateral petals, _i i_, one was twisted out of place, so as partially to occupy the place of the deficient sepal; the lip was represented by two three-lobed segments, _l_, one above and within the other. The column and ovary of this flower were in their normal condition.

Cohesion of two or more segments of the perianth is frequently a.s.sociated with displacements of this nature: thus, in a flower of _Dendrobium n.o.bile_, a diagram of which is given at fig. 48, the uppermost sepal was coherent with one of the lateral ones, and at the same time diminished in size, and, as it were, dragged out of position.

All the other organs of the flower are also more or less displaced, forming a minor degree of the change already alluded to, and which Morren termed speiranthy. The changes will be better appreciated by comparing them with fig. 49, a diagram showing the natural arrangement of parts in this species.

[Ill.u.s.tration: FIG. 48.--Plan of malformed flower of _Dendrobium n.o.bile_.]

[Ill.u.s.tration: FIG. 49.--Plan of natural arrangement in _Dendrobium n.o.bile_. The x x represent processes of the column, perhaps rudiments of stamens.]

Sometimes the displacement seems consequent on hypertrophy of one of the parts of the flower, the disproportionate size of one organ pushing the others out of place. This was the case in a violet, fig. 50, in which one of the sepals _s_ was greatly thickened, and the petals and stamens were displaced in consequence.

[Ill.u.s.tration: FIG. 50.--Plan of flower of violet showing displacement of petals, &c. At _b_ was a rudiment of a stamen.]

It is curious to observe in many of these cases that the transposed organ not only occupies the place of a suppressed or abortive organ, but frequently a.s.sumes its colour, and, to some extent, its function.

This has been alluded to in the case of the leaf of _Gesnera_ (see p.

88) and in Orchids this replacement seems to be very common; thus, in addition to the cases before mentioned, in a flower of an Odontoglossum, for which I am indebted to Professor Oliver, the two lateral sepals were united together and occupied the position of the labellum, which was absent. A similar occurrence happens occasionally in _Lycaste Skinneri_, thus recalling the structure of _Masdevallia_, where the labellum is normally very small. The arrangement in Lycaste may thus be symbolised:

S P st P + S S ___

[Transcriber's note: The underscores represent a horizontal curly brace in the original.]

the + indicating the position of the absent labellum.

Cases of this kind are the more interesting from their relation to the fertilization of these flowers by insects; it seems as though, when the labellum, which performs so important an office in attracting and guiding insects, is deficient, its place is supplied by other means.

Displacement of the parts of the flower from elongation of the receptacle is a not infrequent teratological occurrence, resulting sometimes in the conversion of the verticillate into the spiral arrangement. Instances of this are cited under Elongation, Prolification, &c. In this place it is merely necessary to refer to a curious circ.u.mstance that is met with in some double flowers, owing to this separation of some parts of the flower and the cohesion or adhesion of others. Thus, in some double flowers of _Primula sinensis_ and in the Pea (_Pisum sativum_), I have seen a gradual pa.s.sage of sepals to petals, so that the calyx and corolla formed one continuous sheet, winding spirally around the central axis of the flower, after the fashion of a spiral tube.[98]

=Displacement of the carpels= arises from one or other of the causes above alluded to, and when suppression takes place in this whorl it generally happens that the place of the suppressed organ is occupied by one of the remaining ones, which thus becomes partially dislocated.

=Displacement of the placentas and ovules= is a necessary result of many of the changes to which the carpels are subject. The disjunction or dialysis of the carpels, for instance, frequently renders axile placentation marginal. Moreover, it frequently happens, when the carpels become foliaceous and their margins are disconnected, that the ovules, in place of being placed on the suture, or rather on the margins of the altered carpel, are placed on the surface of the expanded carpel. Thus, in some double flowers of _Ranunculus Ficaria_ that came under the writer's notice the carpels were open, _i.e._ disunited at the margins, and each bore two imperfect ovules upon its inner surface a little way above the base, and midway between the edges of the carpel and the midrib, the ovules being partly enclosed within a little depression or pouch, similar to the pit on the petals. On closer examination the ovules were found to spring from the two lateral divisions of the midrib, the vascular cords of which were prolonged under the form of barred or spiral fusiform tubes into the outer coating of the ovule. In this instance, then, the ovules did not originate from the margins of the leaf, nor from a prolonged axis, but they seemed to spring, in the guise of little buds, from the inner surface of the carpellary leaf.[99]

The occurrence, also, of different forms of placentation in different flowers on the same plant is no unusual thing in malformed flowers; thus, in double flowers of _Saponaria officinalis_ I have met with sutural, parietal, and free central placentation in the same plant.[100]

Professor Babington describes in the 'Gardeners' Chronicle,' 1844, p.

557, a curious flower of _Cerastium_, in which, in addition to other changes, the five carpellary leaves "were partially turned in without touching the placenta, which bears a cl.u.s.ter of ovules, and is perfectly clear of all connection with those part.i.tions" (fig. 51). See also Lindley, 'Veg. Kingdom,' p. 497.

[Ill.u.s.tration: FIG. 51.--1. Monstrous flower of a _Cerastium_; sepals and petals leafy. 2. Stamens and pistils separate. 3. Ovary cut open to show the imperfect dissepiments and the attachment of the ovules. 4. A deformed ovule.]

M. Baillon[101] records flowers of _Bunias_, some with ovules on the margins of the carpels, others with a central branch bearing the ovules; hence he concludes very justly that no fair inference can be drawn from these facts as to the normal placentation of Cruciferae.

The same excellent observer has recorded the occurrence of free central placentation in malformed flowers of _Trifolium repens_.[102]

In malformed flowers of _Digitalis_ the change from axile to parietal placentation may often be seen. Mr. Berkeley describes an instance of this nature where the placentas were strictly parietal, and therefore receded from the distinctive characters of the order, and approximated to those of _Gesneraceae_.

The same author alludes to certain changes in the same flower where two open carpels "were soldered together laterally, as was clear by the rudiments of two styles, the placenta being produced only at the two united edges, the outer margins remaining in the normal condition. This may possibly tend to the explanation of some cases of anomalous placentation, for the only indication of the true nature of the placentation is afforded by the two rudimentary styles, in the absence of which the spongy receptacle of the seeds must have been supposed to spring from the medial nerve."

In other cases the placentas were parietal above, but axile at the base of the capsule, a striking instance of the facility with which axile placentation becomes parietal, the change being here effected by the prolongation of the axis, and the formation on it of a second whorl of carpellary leaves.

In double flowers of _Primulaceae_ similar alterations in the placentation may often be observed. I have seen in _Primula sinensis_ sutural, parietal, axile, and free central placentation all on the same plant; nay, even in the same capsule the ovules may be attached in various ways, and transitions from one form of placentation to another are not infrequent. The late Professor E. Forbes describes[103] an instance of true foliar and true axile placentation in the same flower in _Vinca minor_.

These and many similar changes, which it is not necessary further to allude to, are not so much to be wondered at when it is borne in mind how slight an alteration suffices to produce a change in the mode of placentation, and how frequent is the production of advent.i.tious buds or of foliar outgrowths, as may be seen in the sections relating to those subjects and to Subst.i.tutions.

It will be remembered, also, how, in certain natural orders, under ordinary circ.u.mstances, considerable diversity in placentation exists, according as the margins of the carpels are merely valvate or are infolded so as to reach the centre. Often this diversity is due merely to the changes that take place during growth; thus, the placentation of _Caryophylleae_, _Cucurbitaceae_, _Papaveraceae_, and many other orders, varies according to the age of the carpel, and if any stasis or arrest of development occurs the placentation becomes altered accordingly.

It is not necessary, in this place, to enter into the question whether the placenta is, in all cases whatsoever, a dependence of the axis, as Payer, Schleiden, and others, have maintained, or whether it be foliar in some cases, axial in others. This question must be decided by the organogenists; teratologically, however, there can be no doubt that ovules may be formed from both foliar and axial organs, and, moreover, that, owing to the variability above referred to, both in what are called natural and in what are deemed abnormal conditions, it can rarely happen that any safe inferences as to the normal or typical placentation of any family of plants can be drawn from exceptional or monstrous formations.

On the subject of placentation the following authors may be consulted:

R. Brown, 'Ann. Nat. Hist.,' 1843, vol. xi, 35. Brongniart, 'Ann. Sc. Nat.,' 1834, ser. 2. i, p. 308. Alph. De Candolle, 'Neue Denkschrift der Allg. Schweizer Gesellsch.,' Band v.

1841, p. 9. Duchartre, 'Ann. Sc. Nat.,' 3rd ser., 1844, vol.

ii, p. 290. Ibid., 'Elem. Bot.,' p. 574; 'Rev. Bot.,' 1846-7, p. 213. Babington, 'Gard. Chron.,' 1844, p. 557. Lindley, 'Elements,' p. 89; 'Veg. King.,' pp. 313, 497, &c. Berkeley, 'Gard. Chron.,' 1850, p. 612. Unger, 'Nov. Act. Acad. Nat.

Cur.,' 1850; and in Henfrey's, 'Bot. Gazette,' 1851, p. 70.

Schleiden, 'Principles,' English edit., p. 385. Payer, 'Elem.

Bot.,' pp. 196, 211, 224. Baillon, 'Adansonia.' iii, p. 310.

tab. iv. Cramer, 'Bildungsabweichungen,' p. 20, &c. Clos, 'Ann.

Sc. Nat.,' 5th ser., iii, 313, as well as any of the general treatises on botany. Reference may also be made to the chapters on Prolification and Subst.i.tutions (in the case of the carpels and ovules), and to the authorities therein cited.

FOOTNOTES:

[90] 'Tijdschr. voor. nat. Gesch.,' viii, 1841. tab. ii, p. 178.

[91] Communication to the Internat. Bot. Congress, Paris, 1867.

[92] 'Bot. Zeit.,' 1859, p. 117, tab. v.

[93] 'Ann. Sc. Nat.,' ser. 2, vol. iv, 1835, p. 143. tab. v.

[94] See Kirschleger, 'Flora.' 1844. p. 566 (_Scabiosa_).

[95] 'Bull. Acad. Belg.,' t. xvii. part ii, p. 387.

[96] 'Clos. Mem. Acad. Toulouse,' 5th ser., t. vi. pp. 51, 70.

[97] 'Bull. Acad. Roy. Belg.,' xviii. part ii, p. 505, and vol. xvii, part i, p. 196, and vol. xix. part i. p. 260.

[98] See also Schlechtendal, 'Bot. Zeit.,' iv, p. 804. _Primula veris, partibus perigonii spirae in modum confluentibus._

[99] Seemann's 'Journal of Botany,' vol. v, 1867, p. 158.

[100] 'Journ. Linn. Soc.,' i, 1857, p. 161. _c. xylog._

[101] 'Adansonia,' ii, 306.

[102] 'Adansonia,' iv, p. 70, t. i.

[103] Henfrey's 'Bot. Gazette,' i, 265.