FOOTNOTES:

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 leavesalready referred to at p. 446. In some flowers ofDatura fastuosaa 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" ofGloxinia, 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 adventitiouslobes 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 genusCitrus, may be mentioned under this head. A similar formation occurs in the fruit of some species ofSolanum. (See p. 316.)

FOOTNOTES:[518]It is desirable in this place to allude to a singular case of fissiparous division of a leaf ofPrunus Laurocerasusdescribed by Prof. Alexander Dickson ('Seemann's Journ. Botany,' vol. v, 1867, p. 323), and which did not come under the writer's notice till after the sheet relating to fission, p. 61, had been sent to press. Dr. Dickson thus speaks of this abnormal leaf:—"The petiole (unchanged) supported two laminæ, placed back to back, and united by their midribs (i.e.not separated) to within about an inch from their extremities, which were perfectly free from each other. These laminæ stood vertically, their edges being directed towards and away from the axis; and as they were placed back to back, the shining surfaces, corresponding in structure to the normal upper leaf-surface, were directed laterally outwards. In the axil of this abnormal leaf were two axillary buds. The existence of two leaf-apices and two axillary buds shows that this was not due to an accidental exuberance of development, but to fissiparous division, which, had it been complete, would have resulted in the replacement of a single leaf by two leaves. The arrangement in Prof. Dickson's leaf may be thus represented: [symbol:)OO(with X above]. The nature of the case may be even better seen by comparison with the normal arrangement, which would be [symbol: (OX turned 90 degrees ccw], while in those cases where the fission of the leaf occurs in the same plane as that of the primary lamina, as where a leaf splits into two lobes at the apex, with a midrib to each, the arrangement is as follows: [symbol: OX turned 90 degrees ccw, with 2 arcs below], the X in all cases representing the position of the axis, the O that of the axillary bud, and the [symbol: (turned 90 degrees ccw] that of the laminæ."[519]Linn., 'Phil. Bot.,' § 274. The term "crispa" is surely preferable to that of Ré, "phyllorhyseme."[520]See C. Morren, "Consid. sur les déformations," &c., in 'Bull. Acad. Belg.,' 1852, tom, xix, part 3, p. 444; and as to ferns, see Moore, 'Nature-Printed British Ferns,' 8vo ed., where numerous illustrations are given.[521]'Bull. Acad. Belg.,' t. xix, p. 224, tab. i; and 'Gardeners' Chronicle,' 1865, p. 865.

[518]It is desirable in this place to allude to a singular case of fissiparous division of a leaf ofPrunus Laurocerasusdescribed by Prof. Alexander Dickson ('Seemann's Journ. Botany,' vol. v, 1867, p. 323), and which did not come under the writer's notice till after the sheet relating to fission, p. 61, had been sent to press. Dr. Dickson thus speaks of this abnormal leaf:—"The petiole (unchanged) supported two laminæ, placed back to back, and united by their midribs (i.e.not separated) to within about an inch from their extremities, which were perfectly free from each other. These laminæ stood vertically, their edges being directed towards and away from the axis; and as they were placed back to back, the shining surfaces, corresponding in structure to the normal upper leaf-surface, were directed laterally outwards. In the axil of this abnormal leaf were two axillary buds. The existence of two leaf-apices and two axillary buds shows that this was not due to an accidental exuberance of development, but to fissiparous division, which, had it been complete, would have resulted in the replacement of a single leaf by two leaves. The arrangement in Prof. Dickson's leaf may be thus represented: [symbol:)OO(with X above]. The nature of the case may be even better seen by comparison with the normal arrangement, which would be [symbol: (OX turned 90 degrees ccw], while in those cases where the fission of the leaf occurs in the same plane as that of the primary lamina, as where a leaf splits into two lobes at the apex, with a midrib to each, the arrangement is as follows: [symbol: OX turned 90 degrees ccw, with 2 arcs below], the X in all cases representing the position of the axis, the O that of the axillary bud, and the [symbol: (turned 90 degrees ccw] that of the laminæ."

[519]Linn., 'Phil. Bot.,' § 274. The term "crispa" is surely preferable to that of Ré, "phyllorhyseme."

[520]See C. Morren, "Consid. sur les déformations," &c., in 'Bull. Acad. Belg.,' 1852, tom, xix, part 3, p. 444; and as to ferns, see Moore, 'Nature-Printed British Ferns,' 8vo ed., where numerous illustrations are given.

[521]'Bull. Acad. Belg.,' t. xix, p. 224, tab. i; and 'Gardeners' Chronicle,' 1865, p. 865.

Under the head of atrophy are included those cases wherein the organs affected are actually present, but in a dwarfed and stunted condition as compared with surrounding parts.

The diminished size is, in such instances, obviously due to a partial development and to an arrest of growth at a certain stage, from the operation of various causes, either external or inherent to the organization itself. It may affect any part of the plant, and exists, in very varying degree, in different instances, being sometimes so slight in amount as not to preclude the exercise of the functions of the part; while in others, the structure is so incomplete that the office cannot be performed. These differences depend, of course, upon the stage of development which the organ had reached when its growth was checked. For practical purposes atrophy may be distinguished from suppression by the fact that in the latter case a certain element of the flower or plant which, under ordinary circumstances, is present, is entirely wanting, while, in the former class, it exists but in a rudimentary condition.

Again, atrophy is to be separated from that general diminution in the size of the whole plant or of distinct parts of that plant which is comprised under the term "nanism." Thus the several dwarf varieties of plants (var.nanæ), or those in which the leaves or flowers are smaller than usual (var.parvifoliæ, v.parvifloræ), are truly regarded as variations, and not as malformations properly so called.

Atrophy is partial and special in its operation, nanism is general.

Under ordinary circumstances atrophy is exemplified by the presence of rudimentary or imperfect organs, as, for instance, inPentstemon,Scrophularia, &c., where one stamen is atrophied.

For convenience sake atrophy may be divided into abortion and degeneration, the first including cases where, from arrest of development occurring at an early stage, organs are present; but in a much smaller and more rudimentary condition than usual, their form and general appearance, except so far as regards their dimensions, not being materially altered. On the other hand, in cases of degeneration, development is not entirely checked, but rather perverted, so that not only the dimensions are lessened, but the form is altered.

The sense in which this term is here understood has been explained in the preceding paragraph. It is only necessary to say further, that cases of abortion are to be distinguished from those of suppression, on the one hand, and those of degeneration on the other. In suppression there is from the first an absolute deficiency of a particular organ. In degeneration the part is present, but in a diminished and perverted condition. In abortion it exists, but in a stunted and dwarfed, but not otherwise permuted state.

Abortion of axile organs.—When the main stem is arrested in its growth, the habit and general appearance of the plant are materially altered, as in the so-called stemless plants,plantæ acaules. In these the internodesare so slightly developed that the leaves are closely crowded in tufts or rosettes. When this shortening of the stem (acaulosia) occurs, without other considerable change in other organs, the deviation is classed under the head of variation rather than of monstrosity; and, indeed, in very many plants, this arrested growth of the axis is the rule rather than the exception. When occurring in an abnormal manner, atrophy of the stem is most frequently attended by other more or less grave alterations in other structures; thus Moquin-Tandon[522]cites an instance ofCamphorosma monspeliaca, wherein the stems presented the form of very short, hard, woody tubercles, thickly clothed with deformed leaves, and invested by a vast number of hairs, longer and more dense than usual. A similar deformity sometimes occurs in an Indian species ofArtabotrys; in these specimens the branchlets are contracted in length, and bear numerous closely packed scaly leaves, densely hairy, and much smaller than ordinary.

Spines and thorns may he looked on as atrophied branches, and seem to result from poorness of soil, as the same plants, which, in hungry land, produce spines, develop their branches to the full extent when grown under more favorable conditions.[523]

In the birch an arrest of development in some of the branches is of common occurrence. The branch suddenly ceases to grow in length; at the same time it thickens at the end into a large bulbous knob, from which are developed a profusion of small twigs, whose direction is sometimes exactly the reverse of that of the main branch. (See p. 347.)

The branches of the common spruce fir, especially the lateral ones, when attacked by a particular species of aphis, are very apt to be developed into a cone-like excrescence.[524]

A shortened condition of the flower-stalks occurs occasionally, greatly altering the general character of the inflorescence. This has been observed in pelargoniums and in the Chinese primrose, in both of which the effect was to replace the umbellate form of inflorescence by a capitate one.

Abortion of the receptacle.—Here may be mentioned those cases of flowers with habitually inferior ovary (real or apparent), in which the receptacle fails, from some cause or other, to dilate as usual. This has already been alluded to under the head of Prolification, Displacements, &c. (pp. 78, 130, &c., figs. 35–37, 64, &c.), and hence requires only incidental comment in this place. There are, however, certain other cases of a similar nature which may here be referred to; such as the abortive condition of the inferior ovary, or rather of the receptacle, that usually encircles the ovary inCompositæandUmbelliferæ. In the former natural order the following plants have been met with in this condition:—*Tragopogon pratense!, *Cirsium arvense,Hypochæris radicata,Senecio vulgaris!,Coreopsis Drummondi. In the latter order,Daucus Carota!Œnanthe crocata!andThysselinum palustre, seem most frequently to have been observed in this state.[525]In some gourds the receptacle may be seenpartially developed only, and forming a kind of cup, from which the true carpels protrude.

Abortion of the leaves.—Arrest of growth in the leaves occurs in different ways; sometimes the whole leaf is smaller than usual; at other times certain parts only are reduced in size; while, in a third class of cases, portions of the leaf are entirely suppressed.

Moquin[526]mentions having seen the leaves ofChenopodium vulvaria, and ofDiplotaxis muralisreduced to a fourth of their natural size; and he alludes to other cases of the same nature, seen by other observers, inHypericum perforatumandBlitum polymorphum.

Nicandra physaloides[527]has also been met with in a similar condition, which, indeed, is a common result of insect-puncture, and of fungous growth in plants. Those instances in which the leaf is diminished in size, without any attendant malformation in other organs, may be regarded rather as variations than as monstrosities, as in the case of the entire-leaved varieties of those plants which ordinarily have cut or divided leaves,e.g.Plantago Coronopus, var.integrifolia,Papaver Rhœas integrifolia, &c. &c. The same remark may be made of those specimens in which one part of the leaf is developed to a less extent than another, as happens in the submerged leaves of such plants asRanunculus aquatilis,Cabomba aquatica, the spiney leaves ofBerberis, the fenestrated leaves ofOuvirandra, &c. In the illustrations last cited the relative deficiency of one portion, as contrasted with another, takes place as a constant occurrence, and is uniform and regular throughout the whole leaf. When, on the other hand, the deficiency in question happens accidentally and irregularly, the change may be considered as a malformation. One side of the blade of the leaf is frequently affected in this manner, the other portions remaining unaffected. It would appear as if any plant might bethus altered, but the following species appear to be particularly subject to this change:Æesculus Hippocastanum,Digitalis purpurea,Morus alba,Fagus silvatica contracta(hort.),Codiæum variegatumvar.erosum(hort.),Broussonettia papyrifera,Scolopendrium vulgare, &c.

Frequently this irregular diminution in proportion is coexistent with an unusual degree of cleavage or laciniation of the margin, as inAcer platanoides laciniatum,Tilia asplenifolia,Alnus imperialis(hort.),Fagus silvaticavar. (hort.), &c.

In the case of what are sometimes termed interrupted leaves, the laminar portions of the leaf are here and there deficient on both sides of the midrib, leaving small portions of the latter, as it were, denuded and connecting the segments of the laminæ one with the other. This has been observed amongst other plants inVeronica latifolia,Broussonettia papyrifer,Codiæum variegatumvar.interruptum(hort.),Scolopendrium vulgare, &c.[528](See p. 328.)

In some of the leaves which have been already referred to in illustration of the inordinate growth of the cellular portions, the increased development of parenchyma is associated with a contracted state of the midrib and its branches, producing a puckered appearance of the leaf, an exaggerated degree of that change which produces what are termed "folia bullata." In illustration may be cited various species ofMentha,Perilla,Coleus,Fagus silvatica crispa,Cytisus,Laburnumvar., and other forms, cultivated in gardens for their singularity.

Entire absence of the stalk of the leaf occurs normally in sessile leaves; on the other hand the blade of the leaf is only occasionally developed in the phyllodineous Acacias, in some species ofOxalis,Indigofera,Lebeckia,Ranunculus,Bupleurum, &c.

De Candolle,[529]from a consideration ofStrelitzia juncea, in which the petiole alone is developed, was led to the inference that in many monocotyledonous plants the blade of the leaf was never developed, the portion present being the sheath or stalk, unprovided with limb. The correctness of this inference is shown, amongst other things, by the occasional presence of a leaf-blade inStrelitzia junceaitself.

Occasionally the laminar portions of the leaf are completely wanting, leaving only the main ribs, as in the case ofBerberis, while the adjoining figure (fig. 215) represents an instance of a cabbage wherein the innermost leaves are represented by thick fleshy cylindrical bodies corresponding to the midribs of the ordinary leaves. There is in cultivation a variety of the cabbage which constantly presents this peculiarity.

Fig.215.—Inner leaves of cabbage reduced to their midribs.

The suppression of one or more leaflets of a compound leaf has already been referred to at p. 396.

Abortion of the perianth, calyx, and corolla.—Illustrations of partial development in these organs are not rare, under ordinary circumstances, as for instance the "obsolete" calyx of Umbellifers. In the cauliflower the branches of the inflorescence are contracted in length, while their succulence is much increased; at theirextremities they bear crowds of imperfect flowers, in which the calyx only is visible, and that only in a rudimentary and partially developed condition. Imperfect development of the whole or of some of the constituent parts is more common in the case of the corolla than in that of the calyx. InArenaria serpyllifoliathe petals, especially in autumn, are only one fourth the length of the sepals.Anagallis phœnicea,Honckenya peploides,Arabis alpina,Ranunculus auricomus,Rubus fruticosus, andGeranium columbinum, also frequently afford illustrations of this circumstance.

Fig.216.—Abortion of four out of five petals,Viola tricolor, side and front views.

At fig. 216 is represented a pansy in which four of the five petals were very small and colourless, while the lower spurred petal was of the usual size and colour. In this flower the stamens and pistils were wholly suppressed, and the flower-stalk, instead of being bent near the flower, retained its primary straight direction. Similar atrophic conditions of the corolla occur habitually amongViolaceæ.

The diminished size of the petals sometimes coexists with an increase in their number, as in a flower ofStreptocarpus Rexii, mentioned by Bureau.[530]

Among monocotyledons this partial development seems to be even more frequent than in dicotyledons. In addition to the well-known cases of certain species ofBellevaliaandMuscari, wherein the uppermost flowers of the raceme are more or less atrophied (seep. 347, fig. 179), a few less common illustrations may be cited. In crocuses it is not a very uncommon circumstance to find the three inner segments of the perianth smaller than natural, and generally unequal in size. This occurs without any other perceptible change in the flower.

Schlechtendal[531]mentions a flower ofFritillaria imperialisin which the perianthial leaves were relatively very small, and destitute of the usual nectary, while the stamens, on the other hand, were of their natural size and appearance. Fresenius[532]records a similar occurrence in the same plant.

Morren[533]gives details of like appearances inHymenocallis americana, and Delavaud[534]inTigridia pavonia.

In certain orchids an arrested development of the perianth is habitual, as inOncidium abortivum(fig. 217), where, on a large branching panicle, numerous abortive, but few perfect, flowers are produced. In a similar way the petals and labellum ofOdontoglossum Uro-Skinnerihave been found reduced to filamentous processes.

Fig.217.—Flower ofOncidium abortivum, magnified.

Abortion of the stamens.—Atrophy of one or more stamens is of very common occurrence, as a general rule, in many genera of plants,e.g.Scrophularia,Erodium, manyRestiaceæ, &c. &c. As a strictly teratological condition atrophy of the stamens is more rare than complete suppression. It has been noticed inArabis alpina,Cerastium glomeratum,C. tetrandrum,Rhamnus catharticus,Anemone,Hepatica, &c. It happens frequently among Orchids both wild and cultivated. In theHymenocallisflowers described by the elder Morren, four out of five stamens were atrophied. In other flowers, otherwise perfectly formed, one abortive stamen was found bearing a spherical indehiscent anther. All these atrophied anthers ofHymenocalliswere found to contain pollen, differing at first sight but little from what is usual, but presenting this important peculiarity, that while the normal pollen does not burst until it comes into contact with the stigma, in the abnormal flowers the outer coat of the pollen-grains split while still within the anther, from which latter, indeed, they could not escape, owing to the indehiscent nature of the latter. Again, the pollen-tube of the abnormal grains cracked, in its turn, on mere exposure to the air, and liberated the fovilla, so that the pollen of these atrophied anthers was necessarily impotent, because it opened before it could be applied to the stigma, even had that been rendered possible by the opening of the anther.

An abortive condition of the stamens and of the pollen, is of very common occurrence among hybridised plants. Gaertner and other writers have spoken of this defective condition as contabescence.[535]It forms one reason for the sterility so frequently observed in the case of true hybrids. In some hybrid passion-flowers, while all other parts of the flower were apparently perfect, even to the ovules, the stamens wereatrophied, and distorted, and contained little or no pollen; the few grains of the latter being smaller than usual. (See under Heterogamy, pp. 193–196, and p. 398.)

Abortion of the pistil, fruit, &c.—Traces of the carpels occur in many male flowers of unisexual plants,e.g.Sterculiaceæ,Euphorbiaceæ,Restiaceæ, &c. &c., and in some natural orders there appears to be a tendency towards a diœcious condition,e.g.Caryophylleæ, as inLychnis dioica,Silene otites,Arenaria tetraquetra, &c. The last-named plant is stated to have, in some cases, imperfect pistils; in others, rudimentary stamens; while a third set of flowers are hermaphrodite.[536]The ovary of aconites, according to Moquin, is very subject to atrophy.

Fig.218.—Bladder plum.

During the maturation of the pistil, and its passage to the fruit, great changes of consistence frequentlytake place, owing to the development of cellular tissue, or of woody matter, according as the fruit is succulent or woody. It sometimes happens that, owing to some disturbing causes, the changes that usually occur fail to do so; thus, the stone of plums is occasionally deficient, as in what are termed bladder-plums (fig. 218); some of these, consisting merely of a thin bladder, are curiously like the pods ofColutea.[537]

MM. Fournier and Bonnet[538]describe a fruit of aRubus, with perfectly dry fruits, like those of aGeum, and this form was considered by Steudel to form a distinct species. It is, however, merely a variety in which the fruits have not become succulent.[539]

Schlechtendal describes[540]the ordinarily baccate fruitof a vine as becoming dry, and even dehiscing by valves like a capsule.

In maize it occasionally happens that one or two of the longitudinal series of fruits become abortive, leaving a smooth furrow, at first of a greenish colour, but ultimately of a reddish yellow. Often a second row of fruits, opposite to the first, is also atrophied, so that the whole spike changes its cylindrical form for a flattened one.[541]See also under Heterogamy, Meiophylly, &c.

Abortion of the ovules.—In the case of a pluri-ovulate ovary it rarely happens that all the ovules attain to maturity, some never get fertilised, others, pressed on by their neighbours on either side, become impeded in their development, and finally disappear, or remain as rudiments.[542]This is the case, under ordinary circumstances, and still more so in the case of hybrid plants, or of monsters. Where the outer coats of the ovule become more or less leafy in appearance (see p. 262), the inner investments become more or less atrophied, or are even more frequently entirely suppressed, as is also the nucleus.

In other cases, a simple arrest of development takes place; the ovule, for instance, which should be anatropal, remains straight, while the integuments, checked in their development, form imperfect sheaths from which the shrivelled nucleus protrudes.

Depauperated Ferns.—The preceding illustrations have been taken from flowering plants chiefly, but a similar defective development is manifested in cryptogamous plants. The contraction and imperfect development of the fronds of some varieties of ferns, hence called depauperated, may receive passing notice, as also the cases in which the sori or clusters of spore cases are denuded of their usual covering, owing to the abortionor imperfect development of the indusium, as in what are termed exindusiate varieties.[543]

General remarks on abortion, coincident changes, &c.—Reference has already been made, while treating of hypertrophy, suppression, &c., to certain other changes affecting the flower at the same time. Atrophy of one organ or set of organs, for instance, is frequently accompanied by a compensating hypertrophy or by an increased number of other parts. In the feather-hyacinth,Muscari comosum, var.,monstrosum, the absence of flowers is compensated for by the inordinate formation of brightly coloured threads which appear to be modified pedicels (see pp. 347, 348); so also in the wig plant,Rhus Cotinus. So the atrophy of the stamens, in some flowers, is coincident with the hypertrophy of the pistil. Thus, Unger, 'Denkschr. d. Kais. Acad. der Wissensch. Math. Nat. Classe,' Mai 25, 1848, p. 103, tab. ix, describes a case wherein the corolla and stamens ofDesmodium marylandicumwere atrophied, while the calyx and legume, on the other hand, were hypertrophied.

Fusion of the members of one whorl with one another, or with the components of an adjacent series, often entails atrophy or suppression, either in the united organs themselves, or in adjacent ones. A foliaceous condition of the outer portions of a flower is very generally attended by atrophy or complete suppression of the inner portions.

From this point of view the observations of Morren[544]on the different degrees of atrophy up to complete suppression, observable in the flowers ofBellevalia comosa, are of importance. According to this observer, the most highly differentiated parts, such as the stigmas, the ovules, and the anthers, are the first to disappear,the filaments often being developed without anthers. Ultimately a deformed and empty perianth alone remains. In the ordinary course of things the mouth of the perianth is open, but in some of these malformations it is closed, and when that happens, the effects of atrophy are the more observable in the stamens and pistils.

The impotence of the pollen in certain atrophied flowers, as noticed by the same observer, is of much interest, especially in reference to the sexual relationship between the different forms in polymorphic flowers as studied by Mr. Darwin.

A change in direction may also be noted as a common accompaniment of atrophy or suppression; thus, in a capsule ofVeronica Beccabunga, which was one-celled by the abortion of one carpel, the style was lateral instead of terminal.

As to the causes of these structural deviations but little is known; certain of them have been already alluded to. In some cases atrophy and suppression maybe regarded as permanent states of a condition usually transitory, but this is clearly not always the case. Among external causes anything bringing about an enfeebled condition might be supposed to lead to atrophy, or suppression of some parts.

Gaertner[545]attributes the arrested development and fall of flowers to some among the following causes:—1. non-application of the pollen of the same variety, and consequent imperfect fertilisation; 2. any considerable injury to the calyx, &c.; 3. destruction of the style or stigma before the fertilisation of the ovary; 4. application to the stigma of imperfect or heterogeneous pollen or indifferent pulverulent matter; 5. defective conceptive power in the ovary.

Abortion of the ovules is considered by the same authority to be due to—1. deficiency of heat; 2. excess of moisture; 3. peculiar formation of the ovary; 4. over-luxuriant development of roots or buds; 5. peculiarconditions of cultivation; thus, cuttings and layers produce sterile and abortive seeds much more frequently than plants of the same species raised from seed; 6. abortion of the seed is often combined with luxuriant development of the walls of the fruit.

Temperature and climatal changes in general seem not to be without effect, as has been already mentioned in the case ofArenaria tetraquetra, which is polygamous when growing in mountain districts. Other illustrations of a similar character are mentioned under the head of Heterogamy (p. 196).

Pressure has been already alluded to as one of the most obvious of the inducing causes of atrophy and suppression.

In the case ofRanunculus auricomusbefore cited, in which the petals are rarely perfect, M. de Rochebrune considers that the deficiencies in question depend, in great measure, on the amount of moisture in the localities where the plant grows. In most places the flowers and carpels are apt to become more or less abortive, while the leaves are luxuriant; while, in dry places, the foliage is small, but the flowers are more perfect. This is quite consonant with other facts relating to the development of flowers or of leaves in general.

But while external agencies undoubtedly play some part in bringing about these changes, it is almost certain that internal causes inherent to the organization of the plant are more important. Mr. Darwin[546]accounts for the existence of rudimentary organs by the operation of the general rule of inheritance, and explains their stunted condition as the effect of disuse, not so much, of course, in the particular flower as in its predecessors. This disuse may be the result of the superior efficacy of foreign pollen as contrasted with that formed in the individual flower itself. In this way many hermaphrodite flowers tend to become diœcious, as inCaryophyllaceæ,Orchidaceæ,Plantaginaceæ,Primulaceæand other orders.

Although many of the circumstances above mentioned apply to plants whose structure is habitually rudimentary, there is no reason why they may not, under due restrictions, be applied to plants whose organs are only occasionally defective.

For further remarks on the subject of Abortion, the reader is referred to the sections relating to suppression, etc., also to Moquin-Tandon, 'El. Terat. Veget.,' p. 120; C. Morren, "De l'atrophie en général," in 'Bull. Acad. Belg.,' t. xviii, 1851, part i, p. 275.

FOOTNOTES:[522]'El. Ter. Veg.,' p. 132.[523]Spinosæ arbores cultura sæpius deponunt spinas in hortis, 'Linn. Phil. Bot.,' § 272.[524]Mr. Selby, in his 'History of British Forest Trees,' p. 465, gives the following account of the formation of this peculiar growth:—"In the autumn the parent aphis deposits her eggs at the base of the embryo leaves, within the bud destined to produce the shoots of the following year. When these begin to burst and expand in spring, the leaves, at whose bases the eggs have been deposited, instead of increasing in length, enlarge at the base, and form a cell or cyst whose mouth is at first closed by a red velvety-looking substance. If opened in this state a nest of small greenish aphides is distinctly visible, and at a certain period, or when they have acquired maturity, which is towards the end of the summer, the mouth of the cell opens and the insects fly off to inflict a similar injury upon the nascent buds of the year. In some instances the leaves of only a portion of the circumference of a shoot are affected, in which case, though a slight distortion may take place, the branch is not prevented from elongating; but in others, where the whole of the leaves around the shoot are converted into nidi, elongation is prevented and distortion to a great extent takes place."[525]See Cramer, 'Bildungsabweich.,' pp. 53, 64, for further references.[526]'El. Ter. Veg.,' p. 124.[527]Schlechtendal, 'Bot. Zeit.,' 1857, vol. xv, p. 67.[528]On the subject of this paragraph the reader may consult A. Braun, "Ueber abnorme Blattbildung," &c., in 'Verhandl.,' d. 35, 'Naturforscherversammlung;' Jaeger, 'Flora,' 1850. p. 481, tab. 4,Digitalis.[529]'Org. Veget.,' i. p. 286.[530]'Bull. Soc. Bot. France, vol. viii, 1861, p. 710.[531]'Linnæa,' 1830, vol. v, p. 492.[532]'Mus. Senkenb.,' ii. p. 45.[533]'Bull. Acad. Roy. Belg.,' 1851, t. xviii. part i, p. 275.[534]'Bull. Soc. Bot. France,' vol. viii, 1861, p. 147.[535]See Darwin, 'Variation of Domest. Anim. and Plants,' ii, 165.[536]Gay, 'Ann. Sc. Nat.,' ser. i, 1824, t. iii, p. 44.[537]See De Candolle, 'Mem. Legum.,' tab. 3, f. 1; Wyville Thomson, 'Trans. Bot. Soc. Edinb.,' 1851, July 10th; Berkeley, 'Gardeners' Chronicle,' June 22nd, 1867, p. 654. A similar case is described by Dr. Robb, in Sir W. Hooker's 'Journal of Botany,' 1841, vol. iii, p. 99, with illustrative figures. The specimens there described were produced at New Brunswick, where plum trees flower very freely, but seldom produce ripe fruit. Dr. Robb's account is as follows:—"In the summer of 1839 I had an opportunity of watching the process of destruction among the plums, and it was as follows—Before or soon after the segments of the corolla had fallen off, the ovarium had become greenish yellow, soft, and flabby. As the fruit continued to increase in magnitude, its colour grew darker and of a more ruddy yellow, and at the end of a fortnight or three weeks the size of the abortive fruit rather exceeded that of a ripe walnut. In fact, an observer might imagine himself to be walking amongst trees laden with ripe apricots, but, like the fabled fruit on the banks of the Dead Sea, these plums, though tempting to the eye, when examined, were found to be hollow, containing air, and consisting only of a distended skin, insipid, and tasteless. By-and-bye a greenish mould is developed on the surface of the blighted fruit; then the surface becomes black and shrivelled, and at the expiration of a month from the time of flowering the whole are rotten and decomposed. The flower appears about the beginning of June, and before August there is hardly a plum to be seen. It is curious that where two flower-stalks arise from one point of the branch, one will often go on to ripen in the normal way, while the other will become abortive, as above described."In a specimen described by Mr. Berkeley there were two distinct ovules of equal size close to the apex of the fruit, connected with the base by vessels running down the walls. It should be observed that there is a worthless variety of plum, Kirke's stoneless, or Sans Noyau, in which the kernel is not surrounded by any bony deposit.[538]'Bull. Soc. Bot. Fr.,' 1862, vol. ix, pp. 37 et 291.[539]Carl Schimp, 'Fl. Friburg,' vii, p. 745; Hook, fil., 'Journ. Linn. Soc.,' vi, p. 9.[540]'Linnæa,' vol. v, 1830, p. 493.[541]Moquin-Tandon, 'El. Ter. Veg.,' p. 325.[542]Alph. De Candolle states that the position of the abortive ovules affords a good character for discriminating between certain species ofQuercus, 'Bibl. Univ. Genev.,' 1862, t. xv, p. 929.[543]See Moore, 'Nature-Printed Ferns,' 8vo, for numerous illustrations both of depauperate and exindusiate ferns.Scolopendrium vulgareseems to be one of the ferns most commonly affected in this way. Moore, loc. cit., vol. ii, pp. 135, 147, 159, 165, &c.[544]'Bull. Acad. Belg.,' t. xvii, p. 38, t. 1; Lobelia, p. 85.[545]Cited in 'Henfrey's Botanical Gazette,' i, p. 179.[546]'Origin of Species,' p. 450.

[522]'El. Ter. Veg.,' p. 132.

[523]Spinosæ arbores cultura sæpius deponunt spinas in hortis, 'Linn. Phil. Bot.,' § 272.

[524]Mr. Selby, in his 'History of British Forest Trees,' p. 465, gives the following account of the formation of this peculiar growth:—"In the autumn the parent aphis deposits her eggs at the base of the embryo leaves, within the bud destined to produce the shoots of the following year. When these begin to burst and expand in spring, the leaves, at whose bases the eggs have been deposited, instead of increasing in length, enlarge at the base, and form a cell or cyst whose mouth is at first closed by a red velvety-looking substance. If opened in this state a nest of small greenish aphides is distinctly visible, and at a certain period, or when they have acquired maturity, which is towards the end of the summer, the mouth of the cell opens and the insects fly off to inflict a similar injury upon the nascent buds of the year. In some instances the leaves of only a portion of the circumference of a shoot are affected, in which case, though a slight distortion may take place, the branch is not prevented from elongating; but in others, where the whole of the leaves around the shoot are converted into nidi, elongation is prevented and distortion to a great extent takes place."

[525]See Cramer, 'Bildungsabweich.,' pp. 53, 64, for further references.

[526]'El. Ter. Veg.,' p. 124.

[527]Schlechtendal, 'Bot. Zeit.,' 1857, vol. xv, p. 67.

[528]On the subject of this paragraph the reader may consult A. Braun, "Ueber abnorme Blattbildung," &c., in 'Verhandl.,' d. 35, 'Naturforscherversammlung;' Jaeger, 'Flora,' 1850. p. 481, tab. 4,Digitalis.

[529]'Org. Veget.,' i. p. 286.

[530]'Bull. Soc. Bot. France, vol. viii, 1861, p. 710.

[531]'Linnæa,' 1830, vol. v, p. 492.

[532]'Mus. Senkenb.,' ii. p. 45.

[533]'Bull. Acad. Roy. Belg.,' 1851, t. xviii. part i, p. 275.

[534]'Bull. Soc. Bot. France,' vol. viii, 1861, p. 147.

[535]See Darwin, 'Variation of Domest. Anim. and Plants,' ii, 165.

[536]Gay, 'Ann. Sc. Nat.,' ser. i, 1824, t. iii, p. 44.

[537]See De Candolle, 'Mem. Legum.,' tab. 3, f. 1; Wyville Thomson, 'Trans. Bot. Soc. Edinb.,' 1851, July 10th; Berkeley, 'Gardeners' Chronicle,' June 22nd, 1867, p. 654. A similar case is described by Dr. Robb, in Sir W. Hooker's 'Journal of Botany,' 1841, vol. iii, p. 99, with illustrative figures. The specimens there described were produced at New Brunswick, where plum trees flower very freely, but seldom produce ripe fruit. Dr. Robb's account is as follows:—"In the summer of 1839 I had an opportunity of watching the process of destruction among the plums, and it was as follows—Before or soon after the segments of the corolla had fallen off, the ovarium had become greenish yellow, soft, and flabby. As the fruit continued to increase in magnitude, its colour grew darker and of a more ruddy yellow, and at the end of a fortnight or three weeks the size of the abortive fruit rather exceeded that of a ripe walnut. In fact, an observer might imagine himself to be walking amongst trees laden with ripe apricots, but, like the fabled fruit on the banks of the Dead Sea, these plums, though tempting to the eye, when examined, were found to be hollow, containing air, and consisting only of a distended skin, insipid, and tasteless. By-and-bye a greenish mould is developed on the surface of the blighted fruit; then the surface becomes black and shrivelled, and at the expiration of a month from the time of flowering the whole are rotten and decomposed. The flower appears about the beginning of June, and before August there is hardly a plum to be seen. It is curious that where two flower-stalks arise from one point of the branch, one will often go on to ripen in the normal way, while the other will become abortive, as above described."In a specimen described by Mr. Berkeley there were two distinct ovules of equal size close to the apex of the fruit, connected with the base by vessels running down the walls. It should be observed that there is a worthless variety of plum, Kirke's stoneless, or Sans Noyau, in which the kernel is not surrounded by any bony deposit.

In a specimen described by Mr. Berkeley there were two distinct ovules of equal size close to the apex of the fruit, connected with the base by vessels running down the walls. It should be observed that there is a worthless variety of plum, Kirke's stoneless, or Sans Noyau, in which the kernel is not surrounded by any bony deposit.

[538]'Bull. Soc. Bot. Fr.,' 1862, vol. ix, pp. 37 et 291.

[539]Carl Schimp, 'Fl. Friburg,' vii, p. 745; Hook, fil., 'Journ. Linn. Soc.,' vi, p. 9.

[540]'Linnæa,' vol. v, 1830, p. 493.

[541]Moquin-Tandon, 'El. Ter. Veg.,' p. 325.

[542]Alph. De Candolle states that the position of the abortive ovules affords a good character for discriminating between certain species ofQuercus, 'Bibl. Univ. Genev.,' 1862, t. xv, p. 929.

[543]See Moore, 'Nature-Printed Ferns,' 8vo, for numerous illustrations both of depauperate and exindusiate ferns.Scolopendrium vulgareseems to be one of the ferns most commonly affected in this way. Moore, loc. cit., vol. ii, pp. 135, 147, 159, 165, &c.

[544]'Bull. Acad. Belg.,' t. xvii, p. 38, t. 1; Lobelia, p. 85.

[545]Cited in 'Henfrey's Botanical Gazette,' i, p. 179.

[546]'Origin of Species,' p. 450.

While the terms atrophy and abortion apply in the main to a mere diminution of size, as contrasted with the ordinary standard, degeneration may be understood to apply to those cases in which not only is the absolute bulk diminished, but the whole form is altered and depauperated. Degeneration, thus, is the result not so much of a deficiency in growth as of a perversion of development.

Under natural,i.e.habitual circumstances, the formation of pappus in place of a leafy calyx may be considered as an illustration of degeneration. It is evident, however, that no very decided line of demarcation can be drawn between cases of perversion and of arrest of development.

Formation of scales.—These may be mere epidermal excrescences, or they may be the abortive rudiments of leaves. Of this latter nature are the "cataphyllary" leaves which invest the root stocks of so many perennial plants, the perulæ of leaf-buds, or the paleæ on the common receptacle of composite flowers. Other illustrations of a like character are to be met with in themembranous scales that represent leaves inRuscus,Asparagus,Pinus, &c. Similar productions are met with within the flower, where they may occur as the representatives of sepals, petals, stamens, or pistils, or as mere excrescences. (See Enation.) Whole families of plants,e.g.Sapindaceæ, are characterised by the presence of these organs, which are often of great interest to the morphologist as indicating the true symmetry of the flower, while they have acquired fresh importance since the publication of Mr. Darwin's work on the 'Origin of Species,' wherein we are taught to regard these rudiments as, in many cases, vestiges of organs that were more completely developed in the progenitors of the present race of plants, and the exercise of whose functions, from some cause or other, having been rendered impossible, the structures become, in process of time, proportionately stunted.

Thus, in diœcious plants we frequently find traces of stamens in the female flowers, and rudiments of the pistil in the male flower, indicating, according to the Darwinian hypothesis, that the ancestors of these plants were hermaphrodite (see Heterogamy).

Mr. Darwin has also shown that, in some cases, the utmost degree of fertility is attained, not from the action of the pollen on the stigma of the same flower, but on the influence of the male element of one blossom upon the female organs of another flower on another individual plant.

Hence, in such plants there is a tendency to a separation of the sexes, while, from what has been before stated, it might be expected that rudiments of the male or female organs would be found, and also as a result of the operation of the law of inheritance. On the same principles it is easy to understand the occasional presence of the perfect in place of the rudimentary organs, as inDianthus.

In some instances the assumption of a scale-like form by any organ is attended by a change in texture, the organs becoming dry and scarious, or fleshy.Moquin cites in illustration of the first phenomenon the flower of aVicia, in which the petals were thick and fleshy, like the scales of a bulb; and of the second the leaves of aChrysanthemum, which were replaced by small, glossy scales, like those which invest ordinary leaf-buds. Sometimes the entire flower is replaced by accumulations of small, acute, green scales. Cases of this kind, wherein the flowers of a pea and of the foxglove were replaced by collections of small ovate green scales packed one over the other till they resembled the strobile of a hop, have been already alluded to. Most of these scales are represented as having had other accumulations of scales in their axils.

Similar collections of scales may frequently be met with in the birch and in the oak, and probably represent abortive leaf-buds. Other cases of a like kind inGentiana Amarella, where the scales are coloured, are mentioned elsewhere.

In some kinds ofCampanulaa similar change is not uncommon.

Formation of hairs, spines, &c.—The adventitious production of hairs is likewise frequently due to an arrested growth, in some cases arising from pressure impeding the proper development of the organ. In other cases the formation of hair seems to accompany the diminished development of some organ, as on the barren pedicels of the wig plant,Rhus Cotinus. A similar production of hair may be noticed in many cases where the development of a branch or of a flower is arrested, and this occurs with especial frequency where the arrest in growth is due to the puncture of an insect, or to the formation of a gall. In such cases the hairs are mere excrescences from the epidermis.

Prickles differ but little from hairs save in their more woody texture, but true spines or thorns are modifications either of a leaf or of a branch. Their presence seems often dependent on the soil in which the plants grow, or on other external circumstances.

They occur normally in the sepals ofParonychia serpyllifoliaand other plants.

Formation of glands.—Under this name are associated a number of (generally) rudimentary organs very different in their morphological nature and significance, and also in their functions. Some are truly glandular or secreting organs, while others have no visible office. Anything like a complete account of these structures would be out of place, and reference is only made to them here on account of the occasional existence of intermediate forms, which throw light on the morphological significance of these structures. Thus, inPassifloraandViburnum Opulus, the so-called glands on the sides of the petiole appear to represent leaflets, and are not unfrequently developed as such.

M. Dunal observed a flower ofCistus vaginatusin which some of the stamens were replaced by an hypogynous disc.[547]Moquin has seen similar instances in the flowers of a Rose,Hypericum, and Poppy.

M. Planchon[548]gives an account of some very curious malformations inDrosera intermedia, which go to show that the ovules are homologous with the glandular hairs on the margins of the leaves of these plants, an opinion corroborated by the researches of MM. Grönland and Trécul.[549]

Dr. Hooker shows that the pitcher ofNepenthesis due to a modification of a gland placed at the extremity of the midrib.[550]

Formation of tendrils.—These are of very varied morphological import; sometimes they are degenerated peduncles, as in passion-flowers, or vines; at other times they are of foliar origin; or, again, they may proceed from the segments of the perianth, as inHodgsoniaand some other cucurbitaceous plants. From their very different origin in different plants it is necessary to study the development in each case, and not apply to the generality what may be peculiar to one. In any case this formation in question generally belongs more to general morphology than to teratology.[551]

Kirschleger, however, has recorded the existence of a cirrhose sepal inCucurbita Pepo.[552]

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