Many of the instances that occur of scales projecting from petals, as in Caryophylleae, Sapindaceae, &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 Leguminosae, 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 laminae 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.



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. feroae, and, to a less extent, bullate leaves, may also be mentioned here as illustrations of hypertrophy or enation.



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 Caryophylleae, Sapindaceae, &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.



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.



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.



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 deg., 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.)

FOOTNOTES:

[518] It is desirable in this place to allude to a singular case of fissiparous division of a leaf of Prunus Laurocerasus described 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 laminae, 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 laminae 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 forming a half circle], 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 laminae."

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

[520] See C. Morren, "Consid. sur les deformations," &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.



PART II.

ATROPHY.

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. nanae), or those in which the leaves or flowers are smaller than usual (var. parvifoliae, v. parviflorae), 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, in Pentstemon, 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.



CHAPTER I.

ABORTION.

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, plantae acaules. In these the internodes are 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 of Camphorosma 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 of Artabotrys; 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 in Compositae and Umbelliferae. In the former natural order the following plants have been met with in this condition:—*Tragopogon pratense!, *Cirsium arvense, Hypochaeris radicata, Senecio vulgaris!, Coreopsis Drummondi. In the latter order, Daucus Carota! OEnanthe crocata! and Thysselinum palustre, seem most frequently to have been observed in this state.[525] In some gourds the receptacle may be seen partially 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 of Chenopodium vulvaria, and of Diplotaxis muralis reduced to a fourth of their natural size; and he alludes to other cases of the same nature, seen by other observers, in Hypericum perforatum and Blitum 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 Rhoeas 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 as Ranunculus aquatilis, Cabomba aquatica, the spiney leaves of Berberis, the fenestrated leaves of Ouvirandra, &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 be thus altered, but the following species appear to be particularly subject to this change: AEesculus Hippocastanum, Digitalis purpurea, Morus alba, Fagus silvatica contracta (hort.), Codiaeum variegatum var. 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 in Acer platanoides laciniatum, Tilia asplenifolia, Alnus imperialis (hort.), Fagus silvatica var. (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 laminae one with the other. This has been observed amongst other plants in Veronica latifolia, Broussonettia papyrifer, Codiaeum variegatum var. 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 of Mentha, Perilla, Coleus, Fagus silvatica crispa, Cytisus, Laburnum var., 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 of Oxalis, Indigofera, Lebeckia, Ranunculus, Bupleurum, &c.

De Candolle,[529] from a consideration of Strelitzia 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 in Strelitzia juncea itself.

Occasionally the laminar portions of the leaf are completely wanting, leaving only the main ribs, as in the case of Berberis, 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.



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 their extremities 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. In Arenaria serpyllifolia the petals, especially in autumn, are only one fourth the length of the sepals. Anagallis phoenicea, Honckenya peploides, Arabis alpina, Ranunculus auricomus, Rubus fruticosus, and Geranium columbinum, also frequently afford illustrations of this circumstance.



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 among Violaceae.

The diminished size of the petals sometimes coexists with an increase in their number, as in a flower of Streptocarpus 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 of Bellevalia and Muscari, wherein the uppermost flowers of the raceme are more or less atrophied (see p. 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 of Fritillaria imperialis in 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 in Hymenocallis americana, and Delavaud[534] in Tigridia pavonia.

In certain orchids an arrested development of the perianth is habitual, as in Oncidium 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 of Odontoglossum Uro-Skinneri have been found reduced to filamentous processes.



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, many Restiaceae, &c. &c. As a strictly teratological condition atrophy of the stamens is more rare than complete suppression. It has been noticed in Arabis alpina, Cerastium glomeratum, C. tetrandrum, Rhamnus catharticus, Anemone, Hepatica, &c. It happens frequently among Orchids both wild and cultivated. In the Hymenocallis flowers 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 of Hymenocallis were 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 were atrophied, 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. Sterculiaceae, Euphorbiaceae, Restiaceae, &c. &c., and in some natural orders there appears to be a tendency towards a dioecious condition, e.g. Caryophylleae, as in Lychnis 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.



During the maturation of the pistil, and its passage to the fruit, great changes of consistence frequently take 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 of Colutea.[537]

MM. Fournier and Bonnet[538] describe a fruit of a Rubus, with perfectly dry fruits, like those of a Geum, 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 fruit of 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 abortion or 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 of Desmodium marylandicum were 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 of Bellevalia 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 of Veronica 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. peculiar conditions 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 of Arenaria 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 of Ranunculus auricomus before 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 dioecious, as in Caryophyllaceae, Orchidaceae, Plantaginaceae, Primulaceae and 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 general," in 'Bull. Acad. Belg.,' t. xviii, 1851, part i, p. 275.

FOOTNOTES:

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

[523] Spinosae arbores cultura saepius deponunt spinas in hortis, 'Linn. Phil. Bot.,' Sec. 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] 'Linnaea,' 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] 'Linnaea,' 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 of Quercus, '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 vulgare seems 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.



CHAPTER II.

DEGENERATION.

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 perulae of leaf-buds, or the paleae on the common receptacle of composite flowers. Other illustrations of a like character are to be met with in the membranous scales that represent leaves in Ruscus, 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. Sapindaceae, 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 dioecious 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 in Dianthus.

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 a Vicia, in which the petals were thick and fleshy, like the scales of a bulb; and of the second the leaves of a Chrysanthemum, 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 in Gentiana Amarella, where the scales are coloured, are mentioned elsewhere.

In some kinds of Campanula a 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 of Paronychia serpyllifolia and 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, in Passiflora and Viburnum 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 of Cistus vaginatus in 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 in Drosera 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. Groenland and Trecul.[549]

Dr. Hooker shows that the pitcher of Nepenthes is 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 in Hodgsonia and 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 in Cucurbita Pepo.[552]

FOOTNOTES:

[547] 'Consid. Org. Fleur.,' p. 44, pl. ii, fig. 23.

[548] 'Ann. Sc. Nat.,' 3 ser., Bot. ix, pl. 6, ff. 1, 2.

[549] 'Ann. Sc. Nat.,' 3 ser., Bot. 1855, pp. 297, et 303.

[550] 'Trans. Linn. Soc.,' xxii, p. 415.

[551] See Darwin, "On Climbing Plants," 'Journal of Linnean Society,' vol. ix, p. 1.

[552] 'Flora,' 1845, p. 615.



GENERAL CONCLUSIONS.

At the end of many of the preceding sections, and whenever the requirements of the case demanded it, a brief summary of the main facts and of the inferences to be derived from them has been given. It may be useful to give in conclusion a few general remarks on the whole subject.

It will be seen from the numerous facts herein cited, that the so-called monstrous formations (excluding morbid growths the result of disease or injury) present no peculiarities absolutely foreign to the normal organisation of plants. The difference between the natural and monstrous development is one of degree and frequency of occurrence, not of kind.

Deviations from the customary form have been shown to arise from excessive or diminished growth, or from arrested or exalted development. Even in those instances where, for convenience' sake, the term perverted development has been used, it must be understood as applying only to the particular plant or organ under consideration, as the form assumed is perfectly in accordance with the ordinary conformation of some other plant or group of plants.

The period at which malformations occur is a matter of some importance; this is, indeed, implied in the term arrest of development; evolution goes on with growth up to a certain point and is then stopped, and thus changes are brought about in the part affected of a different nature from those dependent on non-development or suppression.

Some malformations are congenital, therefore, while others are acquired—in the former instance the disturbance is coeval in origin, and contemporaneous in its growth and development, with those of the affected part; in the latter case the organ may have attained its ordinary degree of perfection, or at least may have advanced some way towards it, before any deviation shows itself. True chorisis or fission, for instance, is usually a congenital affection, arising at a very early period of development, while enation takes place from structures which are all but complete as to their organisation, even though they may not have attained their full dimensions. The date of appearance is also of consequence in determining the true nature of some changes; it does not always follow, for instance, that because one organ occupies the position of another, it is of the same nature as the one whose place it fills. The presence of anthers on petals or on such organs as the corona of Narcissus does not necessarily constitute those parts actual stamens, but rather staminodes. The true stamens are either wanting, or if present, they are in advance of their imitators as regards their development.

General morphology of the leaf and axis. Homology. Since the time when Goethe's generalisations were adopted by A. P. De Caudolle, special attention has been given to the form and mode of development of the leaf-organ; for as it was well said by Wolff, if once the course of evolution and the structure of the leaf were known, those of the parts of the flower would follow as a matter of course.

It is not necessary, in this place, to pursue the subject of the development and construction of the leaf further than they are illustrated by ordinary teratological phenomena.

From this point of view perhaps the most interesting circumstance is the part that the sheath of the leaf plays.[553] In many cases of so-called metamorphosis, it is the sheath of the leaf that is represented and not the blade. In normal anatomy the sepals, petals, carpels, and even the stamens, as a general rule, correspond to the sheath rather than to the blade of the leaf, as may be seen by the arrangement of the veins. The blade of the leaf seems to be set apart for special respiratory and absorbent offices, while the sheath is in structure, if not in office, more akin to the stem. It would not be easy apart from their position to distinguish between a tubular sheathing leaf and a hollow stem. The development of adventitious growths by chorisis or enation has been frequently alluded to in the foregoing pages, and many illustrations have been given of the power that leaves have of branching in more than one plane, owing to the projection of secondary growing-points from the primary organ. These new centres of development are closely connected with the fibro-vascular system of the leaf, so that no sooner does a new growing point originate, than vessels are formed to connect the new growth with the general fibrous cord, see pp. 355, 445. This leads M. Casimir De Candollo to consider the entire leaf as a composite structure. The morphological unit, says he, is the cellular protrusion or growing point (saillie) and its corresponding fibro-vascular bundle.[554]

The identity, in a morphological point of view, of the leaves and the lateral parts of the flower is so thoroughly recognised that little need be said on that score, save to repeat that the homology of the floral organs is usually not so much with the entire leaf as with its sheath.

The most singular instances of morphological identity are those relating to the sexual organs. We have seen the gradual transition of stamens to pistils, and of pistils to stamens, the development of ovules on the edges of the anther, the co-existence of pollen with ovules on an antheroid body, and, stranger still, the actual development of pollen within the tissues of the ovule itself! From such facts, in addition to what we know of the relative position, internal structure, and mode of development of the organs, it is impossible to avoid coming to the conclusion that, however distinctly these parts may, under ordinary circumstances, be set apart for the performance of distinct functions, morphologically they are homologous.

These ideas may be carried yet farther—the same sort of evidence, which is adduced in support of the morphological identity of leaves with the parts of the flower, may be advanced in confirmation of the opinion, that, morphologically, there is no distinction between axis and leaf. The leaf, according to this view, is a specialised portion of the axis set apart to do certain work, just as the petals, stamens, &c., are leaves told off for distinct uses. It is unnecessary to refer to the intermediate productions linking the leaf-form to that of the axis, all that is requisite here is to point out the facts that teratology lends in support of these views. These may be summed up by the statement that almost all those attributes which morphologists recognise as peculiar to one or the other organ respectively, may be and are manifested by both. We have the stem acquiring the characters of the leaf, and the leaf those of the stem. Thus we have seen leaves, leaf-buds, branches, and flower-buds springing from leaves or leaf-organs;[555] see pp. 174, 177, 445, &c. The structure that we are apt to associate exclusively with one is found to pertain to the other. The arrangement of the vascular cords in the leaf-organ finds its counterpart in the axis, generally, it is true, modified to suit altered circumstances or diverse purposes. In some cases the disposition is absolutely indistinguishable in the two organs. It may then be said that the distinctions usually drawn between axis and leaf are not absolute, and that, however necessary such a separation may be for descriptive or physiological purposes, morphologically the two organs are identical. Again, it may be said that leaf and axis are two phases of the same organ,—an organ capable of existing in its undifferentiated state in the form of a thallus among Cryptogams, but which in the higher groups of plants becomes marked out into separate portions, each portion having its own distinct functions to fulfil for the common benefit of the whole organisation.[556]

Special morphology.—Under this heading brief reference may be made to some of the organs whose morphological nature has been, and still is, much contested. It is clear that for the due elucidation of these matters, development and the comparative investigation of similar structures in different plants must be studied. Teratological data by themselves can no more be trusted to give a correct solution of any particular question, than the evidence furnished by other departments of botanical science taken separately. With this statement by way of caution, allusion may be made to some of the organs whose morphological construction is illustrated by the facts recorded in the present volume.

Calyx-tube.—In descriptive botany it is the common practice to speak of a calyx-tube, by which is meant a tubular or sheathing portion at the base of the flower, below the sepals or calyx-lobes, and distinct or inseparable from the ovary. The question morphology has to solve is whether this tubular structure is to be considered as a portion of the axis, or whether it is to be regarded as composed of the confluent bases of the sepals.

Mr. Bentham, who has recently reviewed the evidence as to the nature of the calyx-tube in his paper on Myrtaceae,[557] still holds to the notion that the "calyx-tube" or "hypanthium" is formed from the concretion of the basal portions of the sepals. He founds his conclusions upon such facts as the following: the circumstance that the point of origin of the leaf is not always the same as the point of disarticulation or separation from the axis, inasmuch as the basal portion of the leaf is often adherent to the stem for some distance, though still recognisable as foliar not axial in its nature. In the same manner, the corolla and androecium may be concrete at the base, so that the stamens are for convenience' sake described as inserted into the tube of the corolla, though it is generally admitted that both stamens and petals are really hypogynous, and it is not usual to consider the corolla-tube up to the divergence of the stamens as part of the receptacle. A similar remark applies to the carpels and placentas. Mr. Bentham further considers that the gradual disconnection of the various whorls, that may be traced in many plants, is a further proof of concretion, rather than of expansion of the axis, but this argument may fairly be met by the consideration that the several whorls emerge at different heights.[558]

Organs originally free and distinct become ultimately combined at the base by the gradual protrusion from the receptacle of a ring or tube under them, as in the stamens of Leguminosae; yet, says Mr. Bentham, no one would propose to describe the staminal tube of monadelphous Leguminosae as part of the receptacle and not of the stamens. Perhaps not, for descriptive purposes, but morphologically it would not be easy to separate such a tube from the receptacle. The principal kinds of malformation which have a bearing on this subject are mentioned at pp. 77-81 and 247, from which it may be seen that the evidence furnished by teratology is conflicting. It would seem, indeed, that while in some families of plants there may be a real calyx-tube, in others the tubular portion is a sheath-like prolongation of the axis. In Primula or Pedicularis, where the venation is clearly laminar, the tubular portion is distinctly calycine. In other cases the so-called calyx-tube seems as certainly to be an expansion of the receptacle, as in Rosaceae, Myrtaceae, Melastomaceae, Passiflora,[559] &c.

Where the petals and stamens are described as being inserted into the throat of the calyx, or are perigynous, it may be assumed as a general rule, subject to but few exceptions, that the so-called calyx-tube is really a portion of the receptacle.[560] After all, this is very much a question of words, and for the following reasons,—very often the base of the calyx does evidently form a tube, and no one can say where the calyx ends and the receptacle begins. Again, many leaves are known to originate in the form of a ring-like protrusion from the axis, and from this primary ring originate secondary developments. Thus the asserted difference between a leaf, with such a history of development, and an axial structure becomes obliterated. From this point of view, peltate leaves like those of Tropaeolum or Nelumbium become very significant. In both the leaf-stalk is cylindrical and traversed, as in the case of all cylindrical leaf-stalks, by a circle of fibro-vascular cords, as in a branch, and which radiate in all directions in the blade of the leaf. Now, if (as often happens to a slight extent) the central portion of the leaf were much depressed, owing to the disproportionate growth of the peripheral, as contrasted with the central portions, we should have a funnel-like or tubular formation, precisely similar to many of the so-called calyx-tubes. And, if we further suppose new growths to originate from the sides of this funnel or tube, by chorisis or enation, we should have the homologue of a tubular calyx, to the inner surface of which are attached petals, stamens, &c. From the consideration of circumstances such as these just detailed, together with that of the arrangement of the vascular cords, M. Casimir De Candolle arrives at the conclusion that the calyx-tube is a ring-like projection from an axis whose further direct development is arrested. The secondary projections or growing-points correspond to the several fibro-vascular cords of the primary ring, and are ultimately developed into sepals, petals, stamens and ovaries (see pp. 394, 509).

Androecium.—The main points of morphological interest relating to the androecium, referred to in this volume, are those concerning the structure of the anther (see p. 292), the compound nature of the stamens in some orders (see pp. 294, 345), and the nature of the androecium in orchids (see p. 380).

Inferior ovary.—Is the pistil always foliar in its morphological nature, or is it, in some cases, as Schleiden taught, formed from the axis alone? To a great extent the reply to this question is dependent on the conclusions that may be arrived at as to the true nature of the calyx-tube. Considered from a teratological point of view, there is no reason for considering the inferior ovary to be purely axial. On the contrary, the evidence derived from this source supports the ordinary opinion that the carpels are invaginated within the expanded top of the flower-stalk and more or less adherent to it. Some of the gourds afford good illustrations of this, the upper part of the carpels in these fruits projecting beyond the axial portion. But this matter loses much of its importance if the morphological identity of axis and leaf-organ be conceded. The carpels in inferior ovaries seldom or never correspond to the lamina of the leaf, and between the vaginal portion of the carpellary leaf, and the axis who shall draw the distinction?

Placentation.—Some botanists have considered the placentas to be portions of the carpel, and have compared the production of ovules on them to the formation of buds on the leaf of Bryophyllum. Others have been led to see in each placenta, even when it is, to all outward appearance, a portion of the carpellary leaf, a direct prolongation from the axis, adherent to the leaf. Teratology shows that ovules may be formed indifferently on leaf-organs or on stem-organs. Sutural, parietal, axile, free-central placentation, and, if there be more forms, all may be met with even in the same ovary (see pp. 96, 508). Now, if there were such special tendencies in the axis, as contrasted with the leaf, to produce ovules, it is hardly likely that such anomalous arrangements as those just mentioned would be as frequent as they are. But as leaves produce other leaves, from their edges or their surfaces, and as they form buds in the same situations, just as axial organs do,[561] there is surely little ground for considering the placentas, or ovuliferous portions of the plant, to be of necessity axial. Here again, much of the difficulty vanishes if the morphological identity of the leaf-form and of the stem-form be admitted.

Structure of the ovule.—The nature of the ovule and of its coverings has been a fertile source of controversy. The teratological data bearing on this subject have been given at pp. 262-272. These data strongly support the notion of the foliar nature of the coatings, and of the axial nature of the nucleus, taking leaf and axis either in the ordinary sense, or as modifications one of the other. It has been shown that the ovular coats may themselves become carpels, and that ovules may be developed upon ovules, p. 268. Whether the intra-carpellary siliques of Cheiranthus, not uncommonly met with (p. 182), are instances of ovular transmutation may be open to doubt.

The axial nature of the nucleus has been inferred from its position, mode of growth, and from its occasionally lengthening into a leafy or even a floriferous shoot. Probably it may occasionally be invested by sheathing coats, more analogous to tubular processes from the receptacle, than to foliar organs, as is the case in Welwitschia. The discussion of this matter, however, pertains rather to normal morphology than to teratology.

Morphology of conifers.—The nature of the pseudo-leaves of Sciadopitys, and probably of other Conifers, is illustrated by teratology, as also is the true constitution of the scale of the cone (see pp. 192, 245, 352), though it must be admitted that little or no light is thrown on that much-contested point—the true nature of the ovule of Gymnosperms.

Relative position of organs.—When organs are considered, not separately, but in their relations to each other, the appearances presented are referable to similar causes. Thus, the separation of parts usually united has been shown to depend on an excess of development, the persistent union of parts, usually separate in the adult state, has been traced to an arrest of the process of development, by no means necessarily coexistent with diminished growth. The diminished or increased number of parts is, in like manner, attributable to analogous causes, as also are the variations in arrangement and form, spoken of under the heads of Displacement, Peloria, Substitution, &c.

In the instance of displacements, it has been shown how slight a change is required to transform the so-called inferior ovary into a superior one. A defective development of the top of the flower-stalk in some cases, in others a lack of union between the tube of the receptacle or of the calyx (comprising in those terms not only the apex of the receptacle, but the base of the sepals) and the carpels, suffice to bring about this change in a character which for systematic purposes is of great value.

Law of alternation.—The circumstances that interfere with the law of alternation may be briefly alluded to. The deviations from the customary arrangement have been very generally attributed to suppression, or to chorisis. It is unquestionable that either of these affords an efficient explanation of the arrangement in question, as also does that modification of chorisis, as it may be considered, which has been treated of under the head of Enation. Spiral torsion of the axis would likewise bring about analogous results. Still, it is quite conceivable that opposition or superposition of organs may occur without the intervention of any such operations. This will be the more readily conceded when it is remembered that the phyllotaxis of leaves not unfrequently varies on different branches of the same individual tree, and that a similar variation in the flower would at once disturb the customary alternate arrangement. Coalescence of the vascular bundles in an unusual manner, and an irregular disposition of these cords have also been considered to bring about deviations from the rule of alternation, but in general the formation of the cords is subsequent to that of the growing points or mamelons.

Adhesions, accompanied by displacements, occasionally produce similar deviations, the nature of which is usually easily detected.

Co-relation.—The importance of this subject first prominently brought into notice by Geoffroy St. Hilaire gains in force daily. Rarely is a malformation an isolated phenomenon, almost always it is associated, from the operations of cause or effect, with some others. Instances of this co-relation have been cited in the preceding pages, and many more might have been mentioned, had the consideration of the relationship between form and function formed part of the plan of this volume. A change in itself slight, often acquires importance from its association with other alterations. This is particularly well seen in the case of the receptacle. Let an ordinarily concave thalamus remain, from defective development, flat, and how great the change in the appearance of the flower. Let the usually contracted receptacle be lengthened, and the whole aspect of the flowers so affected is altered to such an extent that, were their history not known, botanists would have no hesitation in assigning them to widely separate groups in their schemes of classification. Peloria, too, of either form, affords excellent illustrations of the co-existence of one changed condition with another. Not only is the form of one set of organs altered, but the number, the relative proportion, and the direction of the other organs of the flower are altered likewise.[562] Not only is the whole symmetry changed, but the physiological operations carried on in the flower undergo corresponding alterations.

There are certain co-relations which do not appear to have hitherto attracted the attention they merit; such, for instance, is that which exists between the particular period at which an organ is developed and its position and form. In normal morphology this has, to some extent, been worked out, as in the case of definite and indefinite, centrifugal and centripetal inflorescences, and in the definite or indefinite formation of shoots, &c.

Other instances may be cited in the frequent co-existence of regular flowers and definite inflorescence, the terminal position of many peloriated flowers, the relationship between indefinite inflorescence and prolongation of the axis, &c.

Again, the simultaneous evolution of the parts of the flower and their consequent verticillate arrangement, are often associated with the production of different forms from those characteristic of organs developed in succession, and, in consequence, arranged spirally. In the case of simultaneous development we meet with a repetition of whorls, as in what are termed hose-in-hose flowers (flores duplicati, triplicati, &c.), and also with cases of peloria. In instances where the organs are formed successively in spiral order, we meet with such changes as median prolification, petalody, and phyllody. All these are alterations which we might anticipate from the activity of the growing point being checked at a certain stage in the one case, while it is continuous in the other. This relationship between the definite and indefinite modes of growth and the form of the several organs of the flower, is more constant in reality than it may appear to be from a perusal of the lists of genera in the foregoing pages, in which it was not possible to show sufficiently well the comparative frequency of any given changes in individual plants. Had it been possible to give statistics setting forth the frequency of certain deviations in plants or groups having a particular organisation, as compared with the rarity of their occurrence in other plants of a different conformation, these co-relationships would have been rendered much more evident. A hundred different plants, for instance, may be named in any particular list, of which fifty shall be of one type of structure, and the remainder of another. And the co-relative changes in each fifty may appear to be evenly balanced, but so far is this from being the case, that the frequency of the occurrence of a particular change, in one species in the list, may be so great as far to exceed the instances of its manifestation in all the rest put together. This difficulty is only very partially obviated by the addition of the * to signify especial frequency of occurrence of any given malformation in the plants to whose names it is affixed.

Compensation.—But little further need be said on this head. An atrophied condition of one part is generally associated with an hypertrophied condition of another, and scarcely a change takes place in one direction, but it is associated with an inverse alteration in some other. This principle is not universal, and its application must not be unduly strained. It requires specially to be considered in reference to differences in the degree or kind of functional activity exercised by the organs implicated—points beyond the scope of the present volume.

Teratology and classification.—Lastly, there remain to be mentioned the bearings of teratology on systematic botany. There are those who would entirely exclude teratology from such matters. It may be expedient to do so when the object sought is one of convenience and facility of determination only, but when broader considerations are concerned, teratology must no more be banished than variation. In most instances the one differs but in degree from the other. If variation affords aid in our speculations as to the affinities and genealogical descent of species and other groups, so does teratology, and in a far higher degree.

Take the characters of exogens as distinct from endogens; even under ordinary circumstances, no absolute distinction can be drawn between them. There are plants normally of an intermediate character, while, to take exceptional instances, there are exogens with the leaves and flowers of endogens, and endogens whose outward organisation, at any rate, assimilates them to exogens. Diclinous or monochlamydeous plants owe their imperfect conformation to suppression, and may become structurally complete by a species of peloria. Structurally hermaphrodite flowers become unisexual by suppression, or are rendered incomplete by the non-development of one or more of their floral whorls. Hypogynous flowers become perigynous by adhesion, or by lack of separation; perigynous ones become hypogynous by an early detachment from the receptacle that bears them, or by the arrested development of an ordinarily cup-like receptacle.

How the relative position of the carpels and the calyx may be altered has already been alluded to, as has also the circumstance that while it is common to find an habitually inferior or adherent ovary becoming superior or free, it is much more rare to find the superior ovary adherent to the receptacle or to the calyx.[563] Regular and irregular peloria, too, serve to show how slight are the boundaries, not only between different genera, but also between different families.

While, therefore, teratology may be an unsafe guide in strictly artificial schemes, it is obvious that its teachings should have great weight in all philosophical systems of classification.

The questions will constantly arise, does such and such a form represent the ancestral condition of certain plants? Is it a reversion to that form? or is it, on the other hand, the starting point of new forms?

Such questions cannot receive at present any satisfactory answer, but the evidence we have seems to indicate that pre-existing forms were simpler, and less specialised in structure than those now existing, and hence if we meet with malformations of a simple kind, we may consider them as possible reversions; while, if they present features of increased complexity, and more sharply defined differentiation, we may assume them to be evidences of a progressive rather than of a retrogressive tendency.

That monstrosities so called may become the starting points of new forms is proved by circumstance that, in many cases, the peculiarities are inherited so that a new "race" is produced and perpetuated: and if a new race, why not a new species? The difference is one of degree only.

FOOTNOTES:

[553] See Clos., 'Bull. Soc. Bot. Fr.,' 1856, vol. iii, p. 679.

[554] 'Theorie de la Feuille,' p. 26.

[555] An additional illustration of this may be cited, which has been brought under the notice of the writer by Dr. Welwitsch recently, and in which some of the leaflets of the pinnate leaf of a species of Macrolobium were absent, and their place supplied by flowers arranged in cymes.

[556] The presence of a bud at the extremity once considered to be an absolute distinction between branch and leaf, which latter never forms a bud exactly at the apex—is invalidated by the case of the Nepaul barley, p. 174.

[557] 'Journ. Linn. Soc.,' vol. x, p. 103 et seq.

[558] See also the receptacular tube (ovary?) of Baeckea bearing stamens, see p. 183. It would be natural to see stamens springing from the receptacle but not from the ovary.

[559] In Passiflora the organogeny of the flower clearly shows the truth of this assertion, as was indeed shown by Payer and Schleiden.

[560] See Payer, 'Organ. Veget.'

[561] It must, however, be borne in mind that no true leaf-organ has yet been seen with a bud at its exact apex (unless it be the nepaul barley), while in the case of an axial organ such a position of the bud is constant. The nearest approach is in the case of impari-pinnate leaves in which the terminal leaflet is jointed to the common rachis, and in the leaves of some Meliaceae which continue to push forth new leaflets even after the leaf has attained maturity.

[562] A singular instance of co-relation was shown by Mr. Saunders at the Scientific Committee of the Royal Horticultural Society, February 16th, 1868, in a hyacinth with perfectly green, long, tubular, erect, not horizontally spreading flowers.

[563] An illustration of this latter nature in the case of a cherry, which was surmounted by the calyx lobes, precisely as in the case of a pomaceous fruit, has been given at p. 424, adnot.



APPENDIX

DOUBLE FLOWERS.[564]

In ordinary language, the epithet double flowers is applied to flowers of very varied structural conformation. The most common conditions rendering a flower double, in the popular acceptation of the term, are substitutions of petals or petal-like bodies for stamens and pistils, one or both. (See Petalody, p. 283.) Another very common mode of doubling is brought about by a real or apparent augmentation in the number of petals, as by multiplication, fission, or chorisis. (See pp. 66, 343, 371, 376.) Sometimes even the receptacle of the flower within the outer corolla, divides, each subdivision becoming the centre of a new series of petals, as in some very luxuriant camellias and anemones. The isolation of organs which, under ordinary circumstances, are united together, is another circumstance, giving rise, in popular parlance, to the use of the term double flower. (See Adesmy, Solution, pp. 58, 76, 82.) Prolification is another very frequent occurrence in the case of these flowers, while still other forms arise from laciniation of the petals, or from the formation of excrescences from the petals or stamens, in the form of supplementary petal-like lobes. (See Enation, p. 443.)

As these matters are all treated of under their respective headings, it is not necessary to allude to them again in detail. It may be well, however, to allude, in general terms, to the causes which have been assigned by various writers for their formation, and to the means which have been adopted by practical experimenters to secure the production of the flowers often so much esteemed by the florist. It must be admitted that, in spite of all that has been written on the subject, but very little is known about these matters. In the case of the stock the following means have been adopted by cultivators in order to obtain plants bearing double instead of single flowers. There is first the crossing of single flowers with double ones, effected by planting a double-flowered plant in proximity to a single-flowered one; but this, it is obvious, could lead to no important results, since the double flowers, having no pollen, could not possibly influence the seed, which is borne only by the single-flowered plants. Another plan is the degustation of the buds, that is to say, the chewing of the well-formed buds; it is held that the single plants can be recognised by their sweeter taste and greater consistence, and may thus be weeded out; but there is at least the disadvantage attending this method, that the plants, single as well as double, must all be grown up to the period when these buds are tolerably well advanced. A third method which has been adopted is, that of sowing the seeds at a particular lunar epoch, great confidence being placed in the plan of planting them during the last quarter of the moon, but such confidence is found to be misplaced. The plan of removing the stamens has had its supporters, but as this must be done at an early stage of development, and could only influence the result by diverting the vital force which would be expended in the maturation of the pollen, to the perfecting of the seeds, it is obvious that the plan is impracticable for all ordinary purposes, even if in any degree efficient, which from the plasticity of vegetable development, and the faculty of doubling which is inherent in the stock family, is not at all improbable. Still another mark, the presence of a fifth petal in the single or seed-bearing flower, has been held to indicate the assurance of obtaining a crop of double-flowered plants from seeds saved from flowers possessing this peculiarity. To a certain extent, doubtless, this expectation would be realised, owing to the plasticity and inherent quality just alluded to, but the proportion would be too small for any useful practical purpose.

"The gardeners of Erfurt," observes M. Chate, who has written a book[565] on the subject, in which he makes known a means of obtaining double-flowered stocks founded on more than fifty years' practice in his family, "have, for a long time, to a certain extent monopolised the sale of seeds of these plants. To obtain these seeds, the Erfurt gardeners cultivate the flowers in pots, and place them on shelves in large greenhouses, giving them only sufficient water to prevent them from dying. So cultivated the plants become weakened, the pods shortened, and the seeds less numerous, and better ripened; and these seeds give from 60 to 70 per cent. of double flowers.

"The seeds from these plants are said to be mostly of an abnormal shape, which is so striking that experienced cultivators are able to separate those which would furnish double flowers from those which would produce single ones."

M. Chate's method, which he calls the French one, gives still greater results, viz.: 80 per cent. of double flowers, and these produced by very simple means. "When my seeds," he observes, "have been chosen with care, I plant them, in the month of April, in good dry mould, in a position exposed to the morning sun, this position being the most favourable. At the time of flowering I nip off some of the flowering branches, and leave only ten or twelve pods on the secondary branches, taking care to remove all the small weak branches which shoot at this time. I leave none but the principal and the secondary branches to bear the pods. All the sap is employed in nourishing the seeds thus borne, which give a result of 80 per cent. of double flowers. The pods under this management are thicker, and their maturation is more perfect. At the time of extracting the seeds the upper portion of the pod is separated and placed aside, because it has been ascertained that the plants coming from the seeds situated in this portion of the pod, give 80 per cent. of single flowers. They yield, however, greater variety than the others. This plan of suppressing that part of the pod which yields single flowers in the largest proportion, greatly facilitates the recognition of the single-flowered plants, because there remains to be eliminated from among the seedlings only from 10 to 15 per cent.

This separation of the single from the double-flowered plants, M. Chate tells us is not so difficult as might be supposed. The single stocks, he explains, have deep green leaves (glabrous in certain species), rounded at the top, the heart being in the form of a shuttlecock, and the plant stout and thickset in its general aspect, while the plants yielding double flowers have very long leaves of a light green colour, hairy, and curled at the edges, the heart consisting of whitish leaves, curved so that they enclose it completely. Such is the substance of M. Chate's method of securing so large a proportion of double-flowered plants, and then of separating them from the remaining single ones—a method which commends itself to the good sense of the intelligent cultivator."[566]

Signor Rigamonti, a great cultivator of pinks, asserted that he was able to distinguish double from single-flowered pinks, in the seedling state. According to this gentleman, those seedlings which produce three cotyledons in a whorl in place of two, form double flowers. In the case of Primula sinensis the same results occurred. Some had three leaves in a ring, others two; most had the leaves standing one over the other as usual. These were divided into three sets, and when they flowered, the first lot were all double, the second semi-double, the third single. But these statements have not been confirmed by other observers; and the writer can safely assert that seedling pinks occasionally produce three cotyledons, and subsequently single flowers. He has never observed a double flower under these circumstances, though it is true his experience in this matter has been but small.

A writer in Otto's 'Gartenzeitung,' considers that double flowers are a consequence of dryness of soil and atmosphere, and not of a luxurious soil, rich in nutritious matter, having arrived at this conclusion from an observation of the following circumstances:

"Fifty years ago we saw Kerria japonica in a hothouse with single flowers. Twenty years later we met with it in several gardens, in the open air, but always with double flowers. At this time we were assured that single-flowered plants were no more to be found in the whole of Europe, and botanists forming herbaria offered considerable sums for a branch of K. japonica with single flowers. We were requested to take the plant in hand for the purpose of inducing it to produce single flowers. We were advised to plant it out in a rich soil, which was done, but, by chance, the situation was sloping, consequently it did not retain moisture, and all the flowers produced for several years in succession were double. Shortly after, the captain of an English ship again brought plants bearing normal flowers from Japan, which were soon spread over the continent, and of which we received one plant. After three years all the young plants raised from cuttings were double-flowered.