FOOTNOTES:
[510] 'Cat. Plant.,' Lang., p. 113.
[511] 'Bull. Soc. Bot. France,' t. i, 1854, p. 173, and t. xiii, p. 96.
[512] 'Abhandl. Math. Phys. Class.,' Band. iv, Abhandl. i, tab. i.
[513] See Cramer, 'Bildungsabweich,' pp. 62–79, and Fleischer, 'Missbild, der Culturpflanzen.'
[514] Schlechtendal, 'Bot. Zeit.,' 1844, p. 457; 'Linnæa,' xi, p. 301, xiv, p. 363; 'Bot. Zeit.,' 1856, p. 72; Masters, 'Rep. Brit. Assoc.,' Manchester, 1861; Coultas, 'What may be learnt from a tree,' p. 118.
[515] For further details refer to the chapter on Displacements, p. 86.
[516] 'De Antholysi,' p. 42, § 49.
[517] Loc. cit., tab. 2, f. 6.
CHAPTER III.
ENATION.
Under the above heading are included certain forms arising from excess not of growth, but of development, and consisting in the formation of supplementary lobes or excrescences from various organs.
The new formations are not due either to a repetition or to a partition of any organ, but are out-growths from others previously formed.
In prolification and in multiplication the adventitious structures are of independent origin. In fission the new developments grow simultaneously with the older ones, of which, indeed, they are mere repetitions. Moreover, in fission the supplementary lobes do not, in general, project a plan different from that of the original structure, at least in the first instance, though their direction may ultimately become changed.
In enation the new growth projects from a previously formed organ after it has attained to considerable size, or even after its ordinary proportions have been attained, and it sprouts out from the beginning in a plane which is at a considerable angle to that of the parent organ, and it is sometimes of a different structure from it, and has different functions to fulfil.
Many of the instances that occur of scales projecting from petals, as in Caryophylleæ, Sapindaceæ, &c., the coronal filaments of passion-flowers, the cup of Narcissus, the appendages that beset the segments of the perianth in Lilium lancifolium, and other similar growths, may be referred to a like process. In many cases this has been proved by a study of the development of the flower, from which it appears that the growths in question are developed subsequently to the formation of the ordinary floral whorls. It is requisite, however, to be cautious in pronouncing upon the exact nature of these bodies, in the absence of a knowledge of their period and mode of formation. They may be mere outgrowths from one or other of the customary whorls, or they may represent abortive stamens or petals, &c. Where circumstances prevent the course of development from being traced, something may be inferred as to their real nature from their position in regard to the other parts of the flower, from their anatomical structure, and from analogy or comparison with like organs in other plants. The period of their formation is, perhaps, of less importance than was at one time supposed, since it is well ascertained that, in some cases, the formation of the parts of the flower, e.g. the stamens of mallows, follows a centrifugal rather than a centripetal order.
In the case of monstrous developments of this nature too much care can hardly be exercised, and the observer should rarely venture on an explanation of the nature of the case from the evidence afforded by the monstrous growth apart from that to be derived from the study of the development and organization of the normal flower and from analogous formations in allied plants.
Excrescences from axile organs—Warts.—In a preceding paragraph the formation of gnaurs has been alluded to. There are other outgrowths, called warts, occasionally met with in trees, and which are more closely connected with the central tissues of the stem, while at the same time they are not provided with buds, in which two particulars warts differ from gnaurs.
Excrescences of this kind often attain a very large size, and may be seen on old elms and other trees, but, as their formation is probably more pathological than teratological, no further notice of these structures need here be given. No special notice need here be taken of the tubercles on the roots of so many Leguminosæ, nor of the peculiar excrescences on the roots of Taxodium distichum, as these appear to be normal formations. But it may be well to mention in this place an anomalous development which occurs occasionally in Ruscus aculeatus, and in which, from the upper surface of the ordinary flattened leaf-like branch, projects at right angles a second similar branch, so that in section the appearance would be like that of the inverted letter t; thus, [symbol: Inverted upper-case T].
Enation from foliar organs—Leaves.—The development of adventitious lobes from leaves may take place either from their surfaces or their margins. A few illustrations may be given of each. In cabbage leaves a formation of adventitious laminæ projecting at right angles from the primary one may frequently be observed. In the instance figured (fig. 210) the new growths proceeded almost exclusively from the thick midrib, which, in the figure, is shown cut through just above the base. Not only is the ordinary semilunar band of vascular tissue to be here seen, but a similar broken line of vessels exists on the upper side of the leaf-stalk; thus the whole structure resembles that of a stem or a branch as much as that of a true leaf.
Fig. 210.—Section through base of midrib of cabbage leaf, showing supplementary laminæ, &c.
The development of secondary leaves from the surfaces of primary ones (phyllomania, autophyllogeny) has already been alluded to at [p. 355.]
Some of the cases wherein a leaf seems to have a double lamina may be alluded to here, though possibly they would more properly be referred to fission. The appearance presented is as if four wings projected from the midrib, so that a cross section would be nearly in the form of [Symbol: )O( turned 90 degrees.]. In an orange leaf presenting this appearance the lower surface of one lamina was, as usual, dull in colour, while the upper surface of the subjacent lamina was likewise dull; hence the impression might arise that this was an instance of the adhesion of two leaves back to back, but the petioles were not twisted, as they must have been had two leaves thus been united, and neither in the petiole nor in the midrib was there the slightest indication of fusion, the vascular bundles being arranged in a circular manner, not in a horseshoe-like arrangement, as would have been the case had adhesion taken place.[518] ([See p. 33.])
Such leaves as those of the hedgehog holly, Ilex Aquifolium, var. feroæ, and, to a less extent, bullate leaves, may also be mentioned here as illustrations of hypertrophy or enation.
Fig. 211.—Nephrodium molle. Ordinary frond and forked and crested varieties of the same, the crest arising from the inordinate development of the margins of the pinnules.
When the increased development occurs at the margin of the leaves, especially, the result is a wavy or crisped appearance, "folia undulata, vel crispa."[519] These conditions occur normally in such leaves as those of Rumex crispus, Malva crispa, &c., and are developed to an extreme degree in garden varieties of parsley, some kails, &c., as well as in many ferns, but these are probably cases rather of fission than enation as here understood.[520]
Enation from the sepals.—The basal lobes of the calyx in Campanula Medium, under normal circumstances, may be referred to in illustration of this occurrence, while the adventitious spurs on the calyx of some monstrous flowers seem due also to a like cause. These have already been alluded to at p. 315.
Enation from the corolla.—The instances of this are more frequent than in the case of the calyx, and admit of classification according as they occur in polypetalous or gamopetalous flowers, on the outer or inner surface of the petals, &c. Under natural circumstances the formation of scales, lobes, &c., from the petals, as in some Caryophylleæ, Sapindaceæ, &c. &c., may be explained, as already remarked, by this process, rather than by fission, chorisis, or by substitution of petals for stamens, &c. Each case must, however, be examined on its own merits, as it is not safe to decide upon the arrangement of parts in one flower by simply referring to the analogy of others. In the following illustrations the course of development has not, in all cases, been observed, and hence the explanation here given must be taken with some reserve; for should it prove that the adventitious lobes, &c., are formed simultaneously with the ordinary petals, the case will be one of chorisis rather than of enation, as here understood. Again, it may be that the supernumerary organs really represent petals or stamens in disguise, though this hypothesis demands the further assumption (in order to account for the interference with the law of alternation) that suppression of certain organs has taken place.
Taking first those instances in which the supplementary petals appear on the inner surface of the corolla, as being at once the most frequent, and as presenting the closest analogy, with similar conformations, under natural circumstances, certain double-flowered varieties of the Chinese primrose, Primula sinensis, may be mentioned. In these flowers the calyx is normal, the tube of the corolla is traversed by ten vascular bundles, and the limb is divided into ten fimbriated lobes. About halfway up the tube, on the inner surface, are given off five supernumerary petals, opposite to as many lobes of the corolla. Some of the supplementary petals have a stamen in front of them, in the same relative position as in the normal flower. In some cases the back or outer surface of the supplementary petal is turned towards the inner or upper surface of the primary corolla, thus [Symbol: ((turned 90 degrees cw]; while, in other instances, the front of the adventitious lobe is directed towards the corresponding surface of the original petal, thus [Symbol: () turned 90 degrees]. Whether these supernumerary petals are formed by chorisis or by enation cannot, with certainty, be determined without examining the early stages of development.
Fig. 212.—Datura fastuosa. True corolla turned back to show the supernumerary corolla with the petal-like segments attached to its outer surface (reduced).
Of more interest are those instances where the adventitious growth is on the outside of the corolla; thus in a garden azalea there was intermediate between the calyx and the corolla, both of which were normal, a series of five petalodes, alternating with the sepals, and, therefore, opposite to the lobes of the corolla, and adherent with them at the very base, though elsewhere detached. These petalodes were concave on the surface looking towards the calyx, and were there brightly coloured, while the tint of the opposite surface looking towards the corolla was of a duller hue, corresponding with that of the outside of the corolla-tube. This arrangement of the colour was thus precisely similar to that which occurred in the four-winged leaves already referred to at p. 446. In some flowers of Datura fastuosa a similar series of excrescences was observed; the calyx and the corolla were normal within the latter, intervening between it and the stamens was a second corolla produced by duplication, and adherent to the inner surface of this latter were five stamens. So far there was nothing very peculiar; it remains to say, however, that on the outer surface of the second corolla were five petal-like lobes closely adherent to it below, but partially detached above. The colour of the adventitious segments was paler on the outside than on the inner surface, as in the corolla itself. The position of the several parts was such that they were opposite one to the other; hence, while the lobes of the inner corolla were opposite to those of the outer one, the intermediate petalodes were opposite to both; thus:
S S S S S
--------------------------
P P P P P
| X X X X X
|--------------------------
| P P P P P
|st st st st st
The X indicating the position of the petalodes.
Fig. 213.—Gloxinia, with supernumerary segments on the outside of the true corolla.
A still more singular case is that of a variety of the Gloxinia, described originally by Professor Edouard Morren,[521] but which is now becoming common in English gardens. When first observed these flowers were observed to produce petaloid segments outside the ordinary corolla, and partially adherent to (or rather, not completely separated from it) much as in the azalea before mentioned, the outer surface being brightly coloured, like the inner surface of the corolla in ordinary gloxinias. Being encouraged and tended by gardeners, in course of time, instead of a series of petalodes, more or less distinct from one another, a second corolla or "catacorolla" was formed outside the primary one, so that a hose in hose flower was produced, but, in this case, the supplementary flower was formed on the outside and not within the ordinary corolla. Moreover, the disposition of the colour was reversed, for in the outermost corolla the richest hues were on the outer surface, while in the inner or true corolla they were on the inside.
Professor Morren considers the adventitious petalodes as rudiments of so many supplementary flowers, axillary to the calyx, and adnate to the corolla; each lobe then would, in this view, represent an imperfect flower, and the completed catacorolla would be formed of a series of confluent flowers of this description. But this view involves the assumption of the suppression of all the parts of the flower, except the lobes in question.
Fig. 214.—"Catacorolla" of Gloxinia, formed from the union of adventitious petalodes on the outside of the true corolla (after Morren).
The view here propounded that the lobes in question are enations from the true petals, which become confluent, so as to form the catacorolla, is surely more simple, involves no assumptions of suppression of parts; and moreover, is borne out by the examination of some flowers, where the production of these adventitious lobes from the outside of the minute partially developed petals could be distinctly seen.
Enation from the stamens.—An illustration of this process occurred in some double-flowered rhododendrons, which presented the following arrangement of parts:—calyx and corolla normal; within the latter eight petal-like stamens, forming a pseudo-corolla. The appearance presented by the petaloid filaments and anthers was as if they were adnate to the centre of the petals, but, on closer examination, it appeared that the petaloid expansion to which the dilated filament was apparently attached, was equally a part of the stamens; in other words, that the filament was provided with four petal-like wings, two on each side [Symbol: 00 topped by (turned cw 90°, an o above and another ( turned cw above that]. This disposition was well seen in the anther, half of which was, in some cases, petaloid like the filament; in fact, the inner wing of the latter was directly continuous with the petal-like expansion from the anther. A section through the latter showed, going from within outwards, the cut edges of two perfect polliniferous lobes in the centre; and on either side the petaloid wing representing the remaining anther-lobe; outside these were the edges of the remaining wings, one on each side. ([See p. 290], fig. 155.)
Enation from the carpels.—The only instances of this that need be referred to are such cases as those in which spur-like projections, horns, tubercles, or winged expansions, are formed from the surface of the ovary during the course of its development. The extraordinary cornute oranges described and figured by Ferrari, Gallesio, and other writers on the genus Citrus, may be mentioned under this head. A similar formation occurs in the fruit of some species of Solanum. (See p. 316.)