Prolification of the embryo.—This term was applied by Moquin-Tandon to a peculiar condition of the almond (Amygdalus), in which, indeed, it is not of unfrequent occurrence. In these cases one almond encloses within its cotyledons a second embryo, and this, again, in some instances, a third, the little plants being thus packed like so many boxes one within the other. The supplementary embryos are, in the ripe state at least, quite separate and detached one from another. These cases differ from the ordinary instances wherein there is an increased number of embryos in one seed in their position. In the latter case, as often happens in the seeds of the orange, the new products are placed by the side one of another.[146]

For other cases of prolification or the adventitious formation of buds on leaves, roots, &c., see under Heterotaxy.

FOOTNOTES:

[104] Linn., 'Prolepsis,' Sec. vii; Goethe, 'Metamorph.,' Secs. 96, 103, 106.

[105] "Diaphysis inflorescentiarum." Engelmann, 'De Anthol.,' Sec. 85.

[106] 'Flora,' 1844, p. 565.

[107] 'Ann. Sc. Nat.,' ser. 3, vol. v, 1846, p. 64.

[108] 'Bot Zeit.,' vol. xx, p. 382.

[109] 'Miscel. Austriac. Bot.,' vol. i, Vindob, 1778, p. 133.

[110] "Umbellati dum prolificantur, augent umbellulam, ut ex umbellula simplici altera exeat." 'Linn. Phil. Bot.,' Sec. 124.

[111] 'En. Euphorb.,' p. 36.

[112] Meisner. 'Mon. Gen. Polygoni Prodrom.,' p. 20, tab. v, considers the bulbils of this plant to be modifications of the pedicels of the flower.

[113] See A. Braun. 'Ann. Scienc. Nat.,' 4th series, 1860, vol. xiv, p. 13.

[114] "Prolificatio e latere ex calyci communi proles plurimos pedunculatos emittens, fit in compositis aggregatis proprie dictis." 'Linn. Phil. Bot.,' Sec. 124.

[115] 'Bot. Zeit.,' 1857, p. 873. See also 'Verhandl. Nat. Hist. Vereins. Preuss. Rheinl. u. Westphal.,' 1854, t. ix.

[116] "Pannicula spicatim sparsa onusta innumera foetura herbaceorum flosculorum racematim cohaerentium," 'Lobel. Stirp. Hist.,' p. 163. This is the "Besome Plantain, or Plantain with spoky tufts," of Ray, 'Synopsis,' p. 314. Gerard's 'Herbal,' Ed. Johnson, p. 420. Parkinson, 'Theat. Bot.,' p. 494. Baxter, 'Loudon. Mag. Nat. Hist.,' vol. ix. p. 204, and vol. iii, p. 482. fig. 118.

[117] 'Flora.' 1856. p. 706.

[118] 'Flora of Berwick-on-Tweed,' vol. i. p. 38.

[119] 'Adansonia,' vol. iv. 1864, p. 150, tab. vii. 'Gard. Chron.,' November 19th, 1864.

[120] 'Ann. Sc. Nat.,' ser. 3, tom. ii, p. 290; and 'Adansonia,' iii, tab. iv; see also Bureau, in 'Bull. Soc. Bot. France,' x, p. 191.

[121] Baillon, 'Adansonia,' i, 286.

[122] See also figure in 'Hort. Eystett. Ic. Plant. Vern.,' fol. 15, fig. 1. Ranunculus asiaticus.

[123] Duchartre, 'Ann. des sc. nat.,' 3me serie, vol. ii, 1844, p. 293.

[124] Reissek, 'Linnaea,' vol. xvii, 1843, p. 641, tab. xix.

[125] The tube of the calyx in these specimens was traversed by ten ribs, apparently corresponding to the primary ridges of the normal fruit; these ribs were destitute of spines, and the bristly secondary ridges were entirely absent. Those portions of the carpels which were detached from the calyx had each three ribs, a central and two lateral ones, which appeared to be continuous with the ribs of the calyx below,—although in the case of the calyx there were ten, in the case of the carpels six ribs, three to each. This diversity in number is thus explained:—A circle of vascular tissue ran round the interior of the calyx-tube, at its junction with the limb, and at the point of insertion of the petals and stamens. The vascular circle seemed to be formed from the confluence of the ten ribs from below. Of the five ribs in each half of the calyx, the three central ones were joined together just at the point of confluence with the vascular circle, above which they formed but a single rib—that traversing the centre of the carpellary leaf; the two lateral ribs of each half of the calyx seemed to be continuous, above the vascular rim, with the lateral ribs of the carpel; these lateral ribs were connected on either side with the central one by short branches of communication. The disposition of the ten ribs may be thus represented:—

1 1 1 1 1 1 3 2 3 2 3 3 2 3 2 3 1 1 1 1 1 1 1 1 1 1

The lower line of figures represents the calycine ribs, the middle row shows how each of these ribs is divided at the vascular rim, and the uppermost row shows their distribution above the rim. From this it will be seen that six of the calycine ribs divide into three branches, one prolonged upwards as a lateral or median rib into the carpellary leaf, the other running horizontally to join with similar branches sent out from the neighbouring rib; the four intermediate calycine ribs divide into two branches only, which join the side branches of the first mentioned, but have no direct upward prolongation into the carpel. The ten ridges are placed opposite to the sepals and petals.

[126] 'Neue Denkschriften der allgemeine Schweizerischen Gesellschaft,' band 5. 1841. tab. 2.

[127] Bell Salter, 'Gard. Chron.,' March 13th, 1847, and 'Ann. Nat. Hist.,' 1847, vol. xix, p. 471. &c.

[128] 'The Origin and Production of Proliferous Flowers, with the Culture at large for raising Double Flowers from Single, and Proliferous from the Double.' By J. Hill, M.D. London, 1759.

[129] A. de Candolle, 'Neue Denkschriften,' op. cit., p. 9; also Unger as cited in 'Botanical Gazette,' May, 1351. p. 70.

[130] Duchartre, op. cit.

[131] 'Ann. Sc. Nat.,' 1844, vol. i, p. 297.

[132] Maout, 'Lecons Elementaires de Botanique,' vol. ii. p. 488; Ferrari. 'Hesperides.' pls. 271, 315, 405.

[133] Moquin-Tandon, loc. cit., p. 386, &c.; see also Trecul, in the 'Bull. Soc. Bot. France,' tom. i, p, 307.

[134] 'Bull. Soc. Bot. Fr.,' 1863, vol. x, p. 461.

[135] 'Ann. Sc. Nat.,' 1835, p. 65. See also Le Maout, 'Lecons Element.,' vol. ii, p. 426.

[136] 'Proc. Hort. Soc.,' vol. i, p. 39, fig. 2.

[137] See also 'Nat. Hist. Review,' 1865, p. 377.

[138] 'Acad. Roy. Belg.,' April 11th. 1863.

[139] 'Bull. Soc. Bot. Fr.,' tom. iii, 1856, p. 479.

[140] 'Linnaea,' vol. xv, p. 266, c. ic. Caspary, 'Schriften d. Physik.-Oek. Gesell. zu Koenigsberg,' bd. ii, p. 5, tab. iii, fig. 39, &c.

[141] Lindley, 'Veg. King.,' p. 545; also Clarke on the Position of Carpels, Linn. Soc.,' December, 1850. 'Proc. Linn. Soc.,' ii, p. 105.

[142] 'Notulae,' vol. i, Dicot. p. 127. 'Atlas,' pl. xliii.

[143] Moquin-Tandon gives the following references to cases of proliferous roses, but some I have not been able to verify. 'Journ. des Sav.,' 22 Mai 1679. Hottinger, 'Ephem. Nat. Cur.,' dec. 3 ann. 9 et 10, p. 249. Marchant, 'Mem. Acad. Scienc. Paris.' 1707, p. 488. Preussius, 'Ephem. Nat. Cur.,' cent. 7 et 8. App. p. 83. Schuster, 'Act. Acad. Nat. Cur.,' vol. vi, p. 185. Spadoni, 'Mem. Soc. Ital.,' t. v, p. 488. See also at the end of this section for numerous other references.

[144] 'Bull. Acad. Belg.,' t. xx, part ii, p. 271. See also Bellynck, 'Bull. Soc. Bot. Belg.,' t. vi, ex. 'Bull. Soc. Bot. France,' t. xiv, 1867, Rev. Bibl., p. 241. Orchis ustulata.

[145] I have not been able to meet with this, but it is said to contain a paper on prolification, with numerous bibliographical references.

[146] 'El. Ter. Veg.,' p. 364, Adnot.



CHAPTER III.

HETEROTAXY.

Under this category are here included a variety of deviations from the ordinary arrangement and position of parts which cannot conveniently be classed under the preceding or under other headings. The term heterotaxy is intended to apply to the production of organs in situations where, under usual circumstances, they would not be formed. It thus does not include cases of substitution, where one part is replaced by another, or more or less metamorphosed, nor cases of multiplication, nor of prolification which are characterised not only by the production of members in unwonted situations, but also in unwonted numbers. From the very nature of the anomalies, and specially from the scanty knowledge we possess concerning their mode of development, it is not possible to allocate them in all cases correctly, and moreover many of them might as well be placed in one group as in another.

Formation of adventitious roots.—This is of exceedingly common occurrence in a vast number of plants, so much so that in most cases it cannot be considered as in any way abnormal; there are, however, a few instances where the formation of these organs may be considered to come within the scope of teratology, or, at least, where their production is the result of injury or of some unfavorable condition to which the plant is exposed.

Thus the production of adventitious roots on the stem of the vine is considered to be due to untoward circumstances impairing the proper action of the ordinary subterranean roots. So, too, the formation of roots on the upper portions of stems that are more or less decayed below, as in old willows, is to be considered as an attempt to obtain fresh supplies through a more vigorous and healthy channel.

A similar occurrence often arises as a consequence of some injury. Virgil had this circumstance in view when he wrote

"Quin et, caudicibus sectis, mirabile dictu, Truditur e sicco radix oleagina ligno."—'Georg.' Bk. ii.

I have seen many specimens of adventitious roots produced on the olive in the way just mentioned.

In the 'Gardeners' Chronicle,' January 8th, 1853, p. 21, is described a curious formation of roots in the fissure between two divisions of a laburnum stem. In the same journal, January 1st, 1853, p. 4, Mr. Booth mentions the case of a Cornish elm, the trunk of which was divided at the top into two main divisions, and from the force of the wind or from some other cause the stem was split down for several feet below the fork. Around the edges of the fracture, layers of new bark were formed, from which numerous roots issued, some measuring an inch in diameter and descending into the cleft portion of the tree: similar instances must be familiar to all observers.

It may happen that these roots sent down into the cavity of a decaying trunk may, after a time, become completely concealed within it, by the gradual formation and extension of new wood over the orifice of the cavity formed by the death and decay of the old wood. Such is presumed to be the explanation of a specimen of this kind in the possession of the writer, and taken from a cavity in an apparently solid block of rosewood; externally there were no marks to indicate the existence of a central space, but when the block was sawn up for the use of the cabinet-maker, this root-like structure was found in the centre and attached to one end of the cavity.

The production of roots which ultimately serve as props to support the branches, or as buttresses to compensate for the increasing weight of branches and foliage, is also a familiar occurrence. The huge gnaurs and burrs met with occasionally on some trees often produce great quantities, not only of adventitious buds, but of roots also.



The leaves, equally with the stems, have the power of emitting roots under certain conditions, as when the leaves are in close contact with moist soil or as the result of injury. This happens in some plants more readily than in others—Bryophyllum calycinum is a well-known instance. Mr. Berkeley has described the formation of roots from the fractured leaves of celery,[147] and also in a cabbage where a snail "having gnawed a hole into the middle of a leaf at its junction with the stem, a fascicle of roots was formed, bursting through the tissue lining the cavity, and covered with abundant delicate hairs after the fashion of ordinary radicles."



The production of adventitious roots is not limited to the ordinary leaves of the plant, but may be manifested on the cotyledons; thus Irmisch describes cases of this kind in the cotyledons of Bunium creticum and Carum Bulbocastanum.[148] I have figured and described an analogous case in the cotyledons of the Mango (fig. 72).[149]

To this formation of adventitious roots the gardener owes the power he has of propagating plants by cuttings, i.e., small portions of the stem with a bud or buds attached, or in some cases from portions of the leaves, of the roots themselves, or even of the fruit, as in the case of the cactus (Baillon). Care also has to be exercised in grafting certain fruit trees not to allow the grafted portion to be too close to the ground, else the scion throws out roots into the soil, and the object of the cultivator is defeated.



Layering is another garden operation dependent on the formation of these organs, and advantage is also sometimes taken of this tendency of some plants to produce roots when injured to reduce the dimensions of a plant when getting too large for the house in which it is growing. By gradually inducing the production of new roots from the central or upper portions of the stem, it becomes possible, after a time, to sever the connection between the original roots and the upper portion of the trunk, and thus secure a shortened plant.

On the subject of adventitious roots, &c., reference may be made to Trecul, 'Ann. Sc. Nat.,' 1846, t. v, p. 340, et vi, p. 303. Duchartre, 'Elements de Botanique,' p. 219. Lindley, 'Theory and Practice of Horticulture.' Thomson's 'Gardener's Assistant,' pp. 374, et seq.; and any of the ordinary botanical text-books.

Formation of adventitious buds on roots.—One of the characteristics by which roots are distinguished from stems in a general way consists in the absence of buds; but, as is well known, they may be formed on the roots under certain circumstances, and in certain plants, e.g., Pyrus Japonica, Anemone Japonica, &c. What are termed suckers, owe their origin to buds formed in this situation.

If roots be exposed or injured, they will frequently emit buds. The well-known experiment of Duhamel, in which a willow was placed with the branches in the soil and the roots in the air, and emitted new buds from the latter and new roots from the former, depended on this production of adventitious organs of either kind.

Gardeners often avail themselves of the power that the roots have of producing buds to propagate plants by cuttings of the roots, but in many of these cases the organ "parted" or cut is really an underground stem and not a true root.

M. Claas Mulder has figured and described a case in the turnip-radish of the unusual formation of a leafy shoot from the root, apparently after injury.[150] From the figure it appears as if the lower portion of the root had been split almost to the extremity, while the upper portion seems to have a central cavity passing through it. From the angle, formed by the split segments below, proceeds a tuft of leaves, some of which appear to have traversed the central cavity and to have emerged from the summit, mingling with the other leaves in that situation. The production of a flower-bud has even been noticed on the root of a species of Impatiens.

Formation of shoots beneath the cotyledons.—The tigellar or axial portion of the embryo plant, as contrasted with the radicle proper, is very variously developed in different cases; sometimes it is a mere "collar" bearing the cotyledons, while at other times it is of considerable size. Generally it does not give origin to shoots or leaves other than the seed-leaves, but occasionally shoots may be seen projecting from it below the level of the cotyledons. This happens frequently in seedling plants of Anagallis arvensis, Euphorbia peplus, and other species, Linaria vulgaris, some Umbelliferae, &c.[151]

Adventitious formation of leaves.—The term phyllomania has been vaguely applied both to the production of an unwonted number of leaves and to their development in unusual situations. Under the present heading the latter class of cases are alone included. The extraordinary tendency in some Begonias to develop leaves or leafy excrescences from their surfaces is elsewhere alluded to, and is, in reality, a species of hypertrophy or over-luxuriant growth.

In some flowers where the inferior ovary is supposed to be, in part at least, formed by a dilatation of the top of the flower-stalk, leaves have been met with proceeding from the surface of the ovary or fruit, as in Crataegus tanacetifolia, roses, pears, gooseberries, &c. In a specimen of Nymphaea alba I have met with scale-like leaves projecting from the surface of the fruit (or torus?), and which did not appear to be metamorphosed stamens or styles (fig. 76).



For other illustrations of increased leaf-formation, see Multiplication of foliar organs.



Production of leaves on a usually leafless inflorescence.—The development of the bracts of an inflorescence to such an extent that they resemble ordinary leaves is elsewhere alluded to as of common occurrence. It happens far less frequently that leaves are developed on an inflorescence usually destitute of them, without any metamorphosis or substitution, and without any formation of adventitious buds, such as happens in prolification. Such a partial change from a floriferous to a foliiferous branch may be seen in a specimen of Sambucus nigra in the Smithian herbarium in the Linnean Society, where the ultimate branches of the cyme bear small leaves. My attention was directed to this specimen by the Rev. W. Newbould.

Jacquin figures an analogous case in Sempervivum sediforme,[152] in which the branches of the inflorescence were prolonged into leafy shoots.

Sometimes from the side of a flower-stalk or scape, which usually does not bear leaves, those organs are produced. The common dandelion, Taraxacum, sometimes offers an illustration of this, and also the daisy (Bellis).[153] In a specimen of fasciated cowslip given me by Mr. Edgeworth there was a similar formation of leaves on the flattened stalk.

Production of leaves or scales in place of flower-buds.—The position of the leaf and of the flower-buds respectively is, in most plants, well defined, but occasionally it happens that the former is formed where, under ordinary circumstances, the latter organ should be. This may happen without the formation of any transitional organs between the two, and without actual increase in the number of the buds. Where there is evidently a passage from leaf-bud to flower-bud, or vice versa, the case would be one of metamorphy. If the number of buds be augmented, or they be mixed with the flower-buds, then it would be referable to leafy prolification of the inflorescence. There remains a class of cases wherein there is a complete substitution of one structure for the other, it may be without the slightest indication of transition between the two, and without any admixture of leaf-buds among flower-buds, or any absolute increase in the number of organs, as in Prolification. Such a case is represented in fig. 78, which shows a portion of the stem of a species of Valeriana, bearing at the summit, not an inflorescence, but a tuft of leaves without the slightest indication of flowers.

Drs. Hooker and Thomson relate that in Northern India the flowers of Anemone rivularis are very generally absent, and their place supplied by tufts or umbels of leaves.[154] In the collection of the late Mr. N. B. Ward was a specimen of lupin in which the flowers were all absent, and their place supplied by tufts of leaves.



A similar appearance has been noticed in Compositae, and I owe to the kindness of Professor Oliver the communication of a specimen of a species of Bidens from Peru, in which the capitula, instead of consisting of florets, as usual, contained tufts of linear ciliolated bracts within the involucre, without a trace of flowers. In the eleventh volume of the 'Linnaea,' 1837, p. 301, Von Cesati figures and describes an analogous case in Carduus crispus. The same author[1] records a similar instance in the umbel of Seseli coloratum, where the place of the flowers was occupied by stalked tufts of leaves. In the 'Gardeners' Chronicle,' October 6th, 1860, p. 894, is mentioned an instance where the blossoms of the pea were entirely absent, and their place supplied by accumulations of small, ovate, green scales, thus presenting an appearance similar to that brought about by the inordinate multiplication of the sepals in the "wheat-ear carnation," and in the Sweet William, and not unlike the condition met with in Bryophyllum proliferum. In Digitalis purpurea a similar anomaly is sometimes met with.

In the apple I have observed leafy shoots bearing terminal tufts of leaves where the flower should have been, so that what, under ordinary circumstances would be a corymb of flowers, is here represented by a series of tufts of leaves. In the cultivated azaleas also, leafy shoots occupying the position of the flower may occasionally be met with.

In Bouchea hyderabadensis I have seen the inflorescence more than usually branched and covered with little tufts of bracts, without a trace of true flower. A similar condition seems not infrequent in Gentiana Amarella, as I have not only met with the plant myself in this condition, but have been favoured with specimens by Mr. Pamplin, Mr. Darwin, and others. In Phyteuma spicatum an analogous appearance has been recorded.

Among Griffith's collections from Affghanistan is a species of willow (Salix) in which the inflorescence replaced by a much branched panicle, bearing a quantity of minute bracts, in the axils of which nestle numerous small buds. In another specimen the inflorescence preserves its usual catkin-like shape, but the flowers are replaced by little tufts of leaves. M. Germain de Saint Pierre mentions a case wherein the flowers of Alisma parnassifolia were completely replaced by leaf-buds.[155]



Here, also, may be mentioned the curious aggregations of scales which occur in some grasses, in Restiaceae, Juncaceae, and other orders, in which the inflorescence is made up of collections of scales or bracts with no trace of floral structure. Fig. 79 shows this in a species of Willdenovia, and a very good example is figured in a bamboo, Pseudostachyum polymorphum, by General Munro.[156]

"Rose willows" (fig. 80) owe their peculiar appearance to a similar cause, the scales of the catkin being here replaced by closely crowded leaves. These aggregations of scales or leaves are not confined to the inflorescence, but may be found in other parts of the plant, and may be frequently met with in the willow, birch, oak, &c., generally as the result of insect puncture. On the other hand, the production of leaves or leaf-buds in place of flowers is, as is well known, generally the consequence of an excess of nutrition, and of the continuance rather than of the arrest of vegetative development.[157] It has even been asserted that a flower-bud may be transformed into a leaf-bud by removing the pistil at a very early stage of development, but this statement requires further confirmation.[158]

Viviparous plants.—The spikelets of certain grasses are frequently found with some of their constituent parts completely replaced by leaves, like those of the stem, while the true flowers are usually entirely absent. A shoot, in fact, is formed in place of a series of flowers. In these cases it generally happens that the outermost glumes are changed, sometimes, however, even the outer and inner paleae are wholly unchanged, while there is no trace of squamulae or of stamens and pistils within them, but in their place is a small shoot with miniature leaves arranged in the ordinary manner.

The grasses most commonly affected in this manner are Dactylis glomerata!, Poa bulbosa!, Poa annua!, P. trivialis!, pratensis!, alpina!, angustifolia, and laxa, Cynosurus cristatus, Festuca nemoralis, F. ovina!, Glyceria fluitans!, Gl. aquatica, Aira alpina!, caespitosa!, Phleum phalaroides, Lolium perenne!, Alopecurus pratensis!, Agrostis alba, Holcus mollis!



From an examination of the structure of viviparous grasses Von Mohl was led to the conclusion that the lower palea is to be considered as a bract, and not a perianthial leaf, because the base of the palea surrounds the stem or axis of the spikelet entirely, and both its margins cohere towards its lower extremity.[159]

A similar condition occurs not infrequently in Polygonum viviparum, and in Juncaceae, Cyperaceae, &c.

In the genus Allium an analogous formation of little buds or bulbils takes place in lieu of flowers; this is specially the case with A. vineale, the flowers of which are rarely seen.

Other illustrations of a similar character, where the adventitious leaf-buds are mixed in amongst the flower-buds, are cited under the head of Prolification of the Inflorescence.

Formation of buds on leaves.—The formation of little bulbs upon the surfaces or edges of leaves, forming what are called viviparous leaves, has long been familiar to botanists amongst Alliums. Professor Alexander Braun,[160] who has paid much attention to this subject, divides cases of this kind according to the position of the buds; thus, for instance, they are sometimes formed upon the upper portion of the leaf or petiole, as in many ferns, in Nymphaea guineensis, some Arads, &c. The same condition has been met with as a teratological occurrence in the leaves of Cardamine pratensis, Hyacinthus Pouzolzii, Drosera intermedia,[161] Arabis pumila, Chelidonium majus, Chirita sinensis,[162] Episcia bicolor,[163] Zamia, &c.[164] Many species of Begonia possess the power of emitting buds from the petioles and veins of the leaf; the little ramenta or scales which so plentifully beset the surface of some of these plants likewise, in some instances, pass gradually into leaves. B. phyllomaniaca, Mart., is the species best known as manifesting this tendency, but others have it also.[165]

Buds are also very often formed upon the margins of the leaf, the best known instance of which occurs in Bryophyllum calycinum; Weinmann[166] figures an instance of this kind in Alchemilla minima, or they may occur upon the lower surface of the leaf, as in Ornithogalum scilloides and longe-bracteatum. M. Duchartre[167] mentions a case in the tomato in which the leaves gave origin to small leaf-bearing branches, which, of course, must have originated from buds, just in the same way as in the Drosera before mentioned.



Gardeners occasionally avail themselves of this formation of buds from leaves to propagate plants, e.g. Hoya, Gesnera, Gloxinia, &c.

Formation of buds in the pith.—This is said to be a normal condition in the curious Stangeria paradoxa,[168] and Mr. Berkeley records an instance of this in sea-kale[169] (fig. 83) where the crown had been injured, and buds were seen sprouting from its centre.



It will be remarked that the adventitious production of buds, like that of roots, is very often consequent on decay or injury. The Dutch bulb-growers have availed themselves of this latter circumstance in the propagation of hyacinths. Mr. Fortune, who published some articles on this subject in the 'Gardener's Chronicle,'[170] describes two special modes as adopted by these skilful horticulturists—the one to make two or three deep cuts at the base of the bulb, destroying the nascent flower-stalk when, after a time, small bulbs are formed along the edges of the cut surfaces (figs. 84, 85). The other method is effected by scooping out the interior of the base of the bulb, thus leaving exposed the cut ends of the sheathing leaves arranged concentrically; along these lines the new bulbs are, after some time, formed in great numbers (fig. 86).



For the formation of supernumerary leaves on the surface of the normal one, see Multiplication and Hypertrophy.

Production of gemmae in place of spores.—An instance of this is recorded by Dr. Montagne[171] in the case of a moss, Encamptodon perichaetialis, in which, in the interior of the capsule, in lieu of spores numerous minute gemmae of the same nature as those in the cup of Marchantia were seen.

Formation of flowers on leaves.—It is very doubtful whether a flower-bud has ever been found actually on a leaf. Mere adhesion of the pedicels of the leaf, such as happens in Ruscus, in Helwingia, Erythrochiton hypophyllanthus, and a few other plants, is, of course, not really to be considered in the light of an actual growth from the leaf, and it is very doubtful in the present state of our knowledge whether the case of the Nepaul barley should find a place here, but for convenience sake it is placed in this section, as it is uncertain at present where it properly belongs.



This curious plant has been described and figured by Irmisch in the 13th volume of the 'Linnaea,' p. 124, t. iv; also by Professor Henslow, 'Hooker's Journal of Botany,' 1849, vol. i, p. 33, tabs. 2, 3. The lower palea of this plant forms an inverted flower-bud upon its midrib. In some fresh specimens which I have lately examined I find the structure to be as follows:—On each notch of the rachis there are three spikelets (fig. 88), each one-flowered, and each provided with two linear glumes; the outer palea in all cases is three-lobed at the summit, the central lobe being oblong and hollow, forming a kind of hood (figs. 87-89), and covered with hairs, which are directed downwards towards the centre of the plant. The two lateral lobes are more pointed than the central one; like it they are provided with hairs, but the hairs, in this case, are turned away from the centre of the plant. The cavity of the side lobes is generally empty, but that of the central lobe is occupied by a very slender stalk, which is apparently the termination of the midrib, but which is bent inwards at an acute angle, so as to occupy the hollow space (figs. 90-91). On this slender axis are developed two florets, more or less imperfect in their structure. Only one of the florets that I have seen contained a perfect ovary. The tips of the lateral lobes of the paleae in the primary flower are sometimes extended into a long awn. A similar awn may also be occasionally found on the tips of the paleae of the rudimentary florets. The occurrence of an adventitious axial structure with rudimentary flowers has been adduced in support of the opinion that the lower paleae is, at least so far as its midrib is concerned, an axial rather than a foliar structure, but in the present uncertain state of our knowledge as to the morphology of grasses it is hazardous to risk any explanation founded on so exceptional a case as that of the Nepaul barley.[172]

Production of flower-buds in place of leaf-buds.—Under natural circumstances this does not appear to be of so common occurrence as the change above alluded to, but by the art of the gardener the change is often effected. In rhododendrons and in peach trees and roses I have met with this change occurring without human agency. The means adopted by the gardener are such as check the luxuriance of the leaf-shoots,[173] and this is effected in various ways, as by continuous "pinching" or removal of the leaf-buds, by pruning, ringing the bark, confining the roots, limiting the supply of nutriment, and other means all based on the same principle. Some of the Cape bulbs (Cyrtanthus) are known not to produce their flowers till their leaves have received, in some manner, a check. Fires which often destroy the herbage thus have the effect of throwing the plant into bloom. A very remarkable instance is recorded of the production of flower-buds after an injury to the leaf-buds in the 'Bulletin of the Botanical Society of France,' vol. ix, p. 146. It appears that during the war of the French against the Arabs in Algiers, the latter planted several hundreds of Agaves with a view to obstruct the passage of the French cavalry. The soldiers hacked these plants with their sabres, and cut out the central tuft of leaves, or the heart, as gardeners call it. The following season almost every one of these Agaves sent up their large handsome flower-spikes. It is well known that, under ordinary circumstances, these plants do not flower except at long intervals of time.

Presence of flowers on spines.—That the spine, as a contracted branch, should occasionally produce flowers is not to be wondered at, though the occurrence is by no means common. M. Baillon showed at a meeting of the Botanical Society of France ('Bulletin,' vol. v, 1858, p. 316) a branched spine of Gleditschia bearing a flower at the end of each of the sub divisions. This was, therefore, strictly analogous with those cases in which the peduncle is normally spiney.

Formation of flower-bud on the petals.—An instance of this, it is believed, the only one on record, is cited in the 'Gardeners' Chronicle' for 1865, p. 760, by the Rev. M. J. Berkeley, who describes the formation of a flower-bud on the surface of a petal of Clarkia elegans. Reasoning from analogy there seems no reason why buds should not be formed on the petals as well as on the leaves.

Formation of buds on fruits.—This is a point of some moment with reference to the share which the axis takes in the production of "inferior" fruits. A very frequent malformation in pears is one wherein a second pear proceeds from the centre of the first, and even a third from the centre of the second.[174] Pears are occasionally also observed arising either from the axils of the sepals of the primary pear or from the axil of leaves originating on the outer surface of the fruits—using the term fruit in its popular sense. These cases afford strong confirmation of the view that the outer portion of the so-called fruit in these plants is rather to be considered as an expansion and hollowing-out of the flower-stalk, than as formed from the calyx-tube. It is noteworthy that the true carpels and seeds are frequently entirely absent in these cases.[175] Further reference to these fruits will be made under the head of Hypertrophy.

M. Trecul has described and figured an instance in a species of Prismatocarpus, in which a second flower proceeded from the axil of a bract attached to the side of the fruit of the first flower.[176] A similar growth was observed in the fruit of Philadelphus speciosus by M. A. Gris, who observed that the so-called calyx-tube was provided with two small bracts, from the axil of one of which proceeded a small flower-bud.[177]



The fruits of Opuntia Salmiana, O. fragilis,[178] O. monacantha, and of some species of Echinocactus, have been observed to form small fruit-like branches around their summits. M. Napoleon Doumet describes the fruit as ripening as usual, but as being destitute of seeds in the interior; after a little while the fruit begins to wither, and then a circle of small buds, like those of the stem, may be seen at the top of the fruit, each bud springing from the axil of a little tuft of wool and spines found on the fruit. These little buds elongate into long shoots, produce flowers the following year, which flowers exhibit the same peculiarity. Gasparini and Tenore are said to have recorded the same fact as long since as 1832. The specimen from which the figure (fig. 93) was taken produced its fruits in the Royal Gardens at Kew, and is now preserved in the museum of that establishment. The adventitious growth in these cases appears to arise from the tufts of spines, which, it has been suggested, are the homologues of the sepals. There can, however, be little doubt that the outer and lower portion of the fruit of Opuntia and its allies is a dilatation of the flower-stalk. This is borne out by the fruits of Pereskia, which bear leaves on their surface arranged spirally; indeed, the fruits of Pereskia Bleo are mentioned as producing buds from their summits, in the same way as the Opuntia just cited. P. Bleo is said, by M. Delavaud,[179] to present this anomaly as a constant occurrence. On the summit of the primary fruit, arising apparently from the axils of the sepals, or of small leafy bracts in that situation, are a series of fruit-like branches, which, in their turn, are surmounted by others, even to the fourth generation.

The fruits of Tetragonia expansa frequently have attached to their side a secondary flower or fruit in such a position as to lead to the inference that it springs from the upper portion of the peduncle which is dilated to invest the true carpels. In other instances it is due to an adhesion of the pedicel to the side of the fruit. In either case the production of an adventitious bud might be considered as an illustration of prolification of the inflorescence, though not as was supposed by Moquin and others of axillary prolification.[180]

Buds have also been produced artificially on the surface of some of the fruits in the construction of which the axis is supposed to share; thus, the unripe fruits of some species of Lecythis were stated by Von Martius, at a meeting of the German Naturalists at Carlsruhe, to produce buds when placed in the earth. The fruit of these plants is probably of the same nature as that of the Pomaceae, and Baillon[181] succeeded in producing buds on the surface of the inferior ovary of Jussiaea.

Some of the cases just mentioned have been considered to be instances of prolification of the fruit, but the fruit has little to do with the appearances in question.

Formation of adventitious flowers and fruits within the ovary.—This generally arises either from substitution of a flower-bud for an ovule or from prolification; there are certain cases, however, where the new growth seems not to be either due to metamorphosis or to prolification strictly.

The cut, fig. 94, represents a case where, in the dilated upper portion of the ovary of Sinapis arvensis, two flower-buds were found projecting from a raised central line, corresponding, as it would seem, to the midrib, and not to the margins of the carpel. Similar cases have occurred in Nasturtium amphibium, Brassica Rapa, and Passiflora quadrangularis.



In Bromfield's 'Flora Vectensis,' p. 35, the following account is given of an abnormal development in Cardamine pratensis: "On the lower part of the corymb were several seed vessels on pedicels changed from their usual linear to an ovate elliptical figure, so as to resemble a silicula. These, on being opened, were found to contain petals of the usual colour, which in the pods above had burst from their confinement and appeared as semi-double flowers; the valves of the pod answering to the true calyx. * * * From their verticillate arrangement it is evident that these petaloid expansions were not transformed seeds, but simply a development of the common axis within the ovary into an abortive whorl of floral organs, besides which there were evident rudiments both of stamens and germens in the centre of the bundle." Baillon[182] also records a case of the same nature in Sinapis arvensis.



Here, too, may also be mentioned the presence of an adventitious siliqua within the ordinary one attached along the same line as the ovules, and partially divided by a replum into two cavities. In this case there was nothing to indicate the presence of floral envelopes (figs. 94, 95). A similar occurrence has been brought under my notice in some grapes which were observed to be cracking before they were perfectly ripe, and in which adventitious fruits were found within the parent grape, occupying the position of seeds (figs. 96, 97).

Similar anomalous growths are noticed under the heads of Substitution and Prolification.

Formation of stamens within the cavity of the ovary.—The only instance of this that has come under the author's observation occurred in some flowers of Baeckea diosmaefolia, Rudge, for an examination of which he is indebted to Mr. Bentham.



In the normal flower there is a turbinate hollow calyx, whose limb is divided into five serrated lobes; alternating with these latter, and springing from the throat of the calyx, are the petals. Originating from the same annular disk as the petals are the stamens, seven or eight in number. The ovary is partially adherent, is surmounted by a style, and has two or three loculi with an axile placenta, to which several small curved ovules are attached. The malformed flowers did not present anything peculiar in their outer parts, nor did the ovary, partially immersed within the expanded top of the flower-stalk and the calyx-tube, which is continuous with that organ, show externally any indication of the change within. On cutting it across, however, in any direction, numerous perfect stamens (filaments and anthers) were seen projecting from the walls of the cavity (fig. 98). In most of the flowers the ovary was one-celled; but in a few there was the usual axile placenta; yet even in these latter cases the stamens originated from the walls of the cavity, and not from the placenta. The stamens presented different degrees of development; in some cases they were fully formed, the anther-lobes open, and the pollen exposed; while in other instances the filaments were involute or circinate, just as the ordinary stamens are in the unexpanded flower-bud. In some cases imperfect stamens were found, mere barren filaments, with or without rudimentary anthers at the top. In no instance was there a perfect ovule, or, indeed, any trace of ovules. The stamens appeared to be arranged irregularly on the walls of the ovarian cavity; and while they were certainly more numerous at the lower portion (that now generally considered to be formed by the cup-like end of the pedicel), they were not wanting in the upper half of the ovary (or that which is probably formed from the carpellary leaves).



This case differs from most that have been recorded, and in which there has been a more or less complete substitution of anther for carpel, or where the tissues of the carpel have produced pollen, and so taken upon themselves the appearance and functions of anthers. Instances of this latter kind are not uncommon; but in the Baeckea there were perfect stamens proceeding from perfect and completely closed ovaries. Moquin-Tandon[183] cites from Agardh an instance which seems more closely to resemble the state of things in the Baeckea, and which occurred in a double hyacinth, wherein both anthers and ovules were borne on the same placenta. Probably, though the fact is not stated, the ovary of the hyacinth was open; and we are told that the flower was double—that it was, in fact, modified and changed in more organs than one; while in the Baeckea nothing at all unusual was observed till the ovary was cut open. The style was present even in those flowers where there was no axile placenta; hence in these cases it could not be, as Lindley stated it to be in the closely allied Babingtonia, a prolongation of the placenta.[184]

Formation of pollen within the ovules.—This has now been recorded in two instances by Mr. S. J. A. Salter in Passiflora caerulea and in P. palmata,[185] and by the author in Rosa arvensis.[186]



In the case of the passion-flower there were various malformations in the ovaries, which were all more or less split open at the distal end, indicating a tendency towards dialysis. The pollen-bearing ovules were borne on the edges of these ovaries, and presented various intermediate conditions between anthers and ovules, commencing at the distal extremity of the carpel with a bi-lobed anther, and passing in series to the base of the ovary, an antheroid body of ovule-like form, a modified ovule containing pollen, an ovule departing from a perfectly natural condition only in the development of a few grains of pollen in its nucleus, and, finally, a perfect, normal ovule.

In the flowers of the Rose the stamens exhibited almost every conceivable gradation between their ordinary form and that of the carpels, while some of the ovules contained pollen in greater or less abundance. Speaking generally, the most common state of things in these flowers was the occurrence on the throat of the calyx, in the position ordinarily occupied by the stamens, and sometimes mingled with those organs, of twisted, ribbon-like filaments, which bore about the centre one or more pendulous, anatropous ovules on their margins. Immediately above the latter organs were the anther-lobes, more or less perfectly developed, and surmounting these a long style, terminating in a fringed, funnel-shaped stigma. Sometimes the ovules were perfect, at other times the nucleus protruded through the foramen, while in a third set the nucleus was included within the tegument, the ovules having in all respects their natural external conformation, containing, however, not only pollen-grains, but also a layer of those peculiar spheroidal cells, including a fibrous deposit, which are among the normal constituents of the anther. In one case, where the coat of the ovule was imperfect, and allowed the nucleus to protrude, the pollen was evidently contained within the central mass of the structure. In this instance the fibrous cells were not detected, these being only found in cases where the investment of the ovule was perfect; and hence it seems likely that the fibrous cells were part of the coat of the ovule, while the pollen was formed within the nucleus. In no case was any trace of embryo sac to be seen.

The main interest, as Mr. Salter remarks, in these cases is physiological; so far as structure alone is concerned, there does not appear any reason why pollen-grains should not be developed in any portion of the plant; the mother cells in which the pollen is formed not differing, to all outward appearance, from any other cells, unless it be in size.

The fundamental unity of construction in all the organs of plants could hardly be better illustrated than by these cases; while, in spite of their exceptional nature, they must be of great interest physiologically, as showing the wide limits of possible variation which thus may even involve the sex, "for an ovule to develop pollen within its interior," says Mr. Salter, "is equivalent to an ovum in an animal being converted into a capsule of spermatozoa. It is a conversion of germ into sperm, the most complete violation of individuality and unity of sex. * * * * The occurrence of an antheroid ovule and a normal ovule on the same carpellary leaf realises the simplest and the most absolute form of hermaphroditism."

It must, however, be remarked that the term substitution would be preferable to conversion. There is, at present, no evidence to show that the germinal vesicles were present in these cases; on the other hand, it seems most probable that they were not, so that the presence of the pollen-cells must be considered as simply adventitious. It can hardly be that they were, in the first instance, germinal vesicles, which, in course of time, became so modified as to assume the appearance of pollen-grains. Between the nucleus of the ovule and the tubercle of cellular tissue constituting the primordial anther, there is little or no difference, so that it may be said that, for a time, there is no distinction of sex in the nascent flower, but as development goes on, the difference becomes perceptible. It cannot at present be stated what precise circumstances induce the one mass to form mother-cells and pollen-grains, and the other to develop an embryo sac and germinal vesicles. Position and external circumstances may have some indirect effect, and it may, perhaps, be significant that in all the instances of polliniferous ovules, the ovular structures have been exposed on an open carpel or otherwise, in place of being confined within the cavity of a closed ovary, as under ordinary circumstances. Even among Conifers the ovuligerous scales are so closely packed that there is little or no exposure of the ovules. But, apart from all speculative notions as to the relation between the structure and functions of the anther and of the ovule respectively, and of the possibility or the reverse of parthenogenesis, it will clearly be necessary in any future alleged occurrence of the latter phenomenon to ascertain whether any or all of the apparent ovules are, or are not, anthers in disguise.

Homomorphic flowers of "Compositae."—In a large section of the Compositae there is, as is well known, a distinction between the florets of the "disc" and those of the "ray," the latter being ligulate, the former tubular.

In what are erroneously called double flowers in this order, e.g. in the Chrysanthemum, Dahlia, &c. &c., the florets are all ligulate. This change is sometimes classed with peloria, but there is no abnormal regularity in these cases. On the other hand, were the ligulate florets to be all replaced by tubular ones, the term peloria would be more strictly applicable. It will be remembered that in the sub-order Liguliflorae, the florets are naturally all ligulate, so that the change above mentioned is not in itself a very grave one.

Heterotaxy affecting the inflorescence.—Under the head of Prolification, Heterogamy, &c., various deviations from the normal inflorescence are alluded to. In this place, therefore, it is only necessary to mention certain rare deviations from the customary arrangement of the inflorescence, such as the change from a definite centrifugal form of inflorescence to an indefinite centripetal one. This occurs occasionally in roses, where the shoot, instead of terminating in a flower-bud, lengthens and bears the flower-bud on its sides as in a raceme.

In the hyacinth, the inflorescence of which is properly indefinite, the terminal flower may frequently be found to expand first, though in order of development it may have been the last formed.

It occasionally happens that certain plants will, contrary to their usual custom, bloom twice in the same season; this usually arises from the premature development of buds which, under ordinary circumstances, would not unfold till the following spring. In these instances of what the French term "fleuraison anticipee," the position of inflorescence is not changed, but there are other cases where the position of the inflorescence is altered, as in the laburnum, where, in some seasons, racemes may be seen springing from short lateral "spurs" along the sides of the branches, as well as from the extremities of long shoots.

Of a similar nature are those cases wherein stems or branches usually sterile become fertile; this happens in Equisetaceae,[187] in Restiaceae, and other orders. In the equisetums, the condition in question has been specially noticed to occur after prolonged drought.

Equisetaceae are likewise subject to an anomaly called by Duval Jouve interruption of the spike, and wherein the scales bearing the spore cases are separated by whorls of branches instead of forming one compact unbroken spike as usual.

This alternation of the organs of vegetation and reproduction may also be seen occasionally in Typha, and other plants.

Kirschleger describes a case in which the male catkins of Salix cinerea were placed at the ends of the branches instead of being lateral productions; moreover the usual articulation was not formed, so that the catkin was persistent instead of deciduous.[188]

Supra-soriferous ferns.—In the great majority of ferns the sori or clusters of spore cases are placed on the under surface of the fronds; nevertheless, a few cases are on record where the fructification is produced on the upper as well as on the lower surface, and sometimes abundantly so. This occasionally happens from the elongation of the normally placed sorus, which thus extends to the margin, and returns on the upper side, when the sori chance to be placed opposite to the marginal crenatures. But it is also frequently the case that the sori are produced on the upper side, distinctly within the margin, and where there are no corresponding sori beneath. Those varieties which have the margin crenated or lobed seem most liable to assume this abnormal supra-soriferous condition. Among the ferns in which this condition has been observed are the following: Scolopendrium vulgare, Polypodium anomalum, Hook., Asplenium Trichomanes, Cionidium Moorei.[189]

FOOTNOTES:

[147] 'Gard. Chron.' 1852, p. 51.

[148] 'Flora.' 1858, pp. 32-42.

[149] 'Journ. Linn. Soc.,' vol. vi; "Botany," 1862, p. 24.

[150] 'Tijdschrift voor Natuur. Geschied,' 1836, vol. iii, tab. vii, p. 171.

[151] Roeper, 'Enum. Euphorb.,' p. 19. Bernhardi, 'Linnaea,' vii, p. 561, tab. xiv, f. 1. Wydler, "Subcotyled. sprossbildung," 'Flora,' 1850, p. 337. Hooker, 'Trans. Linn. Soc.,' vol. xxiv, p. 20 (Welwitschia).

[152] 'Misc. Austriac. ad Bot.,' vol. i, p. 133, t. 5.

[153] See also Carriere, 'Revue Horticole,' 1866, p. 442; and as to pears, Radlkofer in 'Bericht ueber die Thaetigkert der Baierischen Gartenbau Gesellschaft,' 1862, p. 74, t. i.

[154] 'Flora Indica,' p. 23.

[155] 'Bull. Soc. Bot. Fr.,' 1856, p. 53.

[156] 'Trans. Linn. Soc.' xxvi, p. 142, tab. iv, B.

[157] "Si arbusculam, quae in olla antea posita, quotannis floruit et fructus protulit, deinde deponamus in uberiori terra calidi caldarii, proferet illa per plures annos multos ac frondosos ramos, sine ullo fructu. Id quod argumento est, folia inde crescere, unde prius enati sunt flores; quemadmodum vicissim, quod in folia nunc succrescit, id, natura ita moderante, in flores mutatur, si eadem arbor iterum in olla seritur."—Linnaeus, 'Prolepsis,' Sec. iii.

[158] 'Rev. Hortic.' May, 1868, 'Gardeners' Chronicle,' 1868, pp. 572, 737.

[159] Cited in 'Annals Nat. Hist.,' 1845, vol. xv, p. 177.

[160] 'Ann. Scienc. Nat.,' vol. xiv, 1860, p. 13.

[161] Naudin, 'Ann. Sc. Nat.,' 2nd ser., 1840, vol. xiv, p. 14, fig. 6, pl. i (Drosera). St. Hilaire, 'Comptes Rendus,' ix, p. 437.

[162] Hance, 'Hook. Journ. Botany,' 1849, vol. i, p. 141, pl. v.

[163] Booth, 'Gard. Chron.,' Jan. 1st, 1853, p. 4.

[164] Lindley, 'Theory of Horticulture,' ed. 2, p. 273.

[165] 'Hook. Journ. of Botany,' 1852, iv, p. 206. See also the curious Begonia gemmipara, 'Hook. fil. Illust. Himal. Plant.,' t. xiv.

[166] 'Phytanth.,' n. 36, d.

[167] 'Ann. Scienc. Nat.,' 3rd series. 1853. vol. xix, p. 251, tab. 14.

[168] Carriere, 'Revue Horticole.' 1868, p. 184.

[169] 'Gard. Chron.,' 1858, p. 556.

[170] 1863, p. 556, &c.

[171] 'Ann. Nat. Hist.,' 1845, vol. xvi, p. 355.

[172] See also Lindley, 'Veg. Kingd.,' p. 109 et 116a, where the views of Raspail, R. Brown, Mohl, Henslow, and others, are discussed.

[173] It has been observed that if a plant is supplied with copious nourishment the flowering-period is delayed; but that moderate or even scanty nourishment accelerates it. Goethe, 'Metam.,' Sec. 30. See also Wolff, 'Theoria Generationis,' 1759; Linn. 'Prolepsis,' Secs. 3 and 10.

[174] Moquin-Tandon, p. 384; also Lindl., 'Elements of Botany,' p. 65, fig. 130; "Theory of Horticulture," p. 86. 'Gard. Chron.,' 1851, p. 723; Irmish, 'Flora,' 1858, p. 38, &c.

[175] Caspary, 'Bull. Soc. Bot. Fr.,' vol. vi, 1859, p. 235; also Payer, ibid., vol. i, 1854. p. 283.

[176] Trecul, 'Ann. Sc. Nat.,' 2nd ser., vol. xx, p. 339.

[177] 'Bull. Soc. Bot. Fr.,' vol. vii, 1858, p. 331.

[178] 'Bull. Soc. Bot. Fr.,' vol. i. p. 306, vol. v, p. 115. 'Illustr. Hortic.,' xii, 1865, Misc. 79. 'Rev. Horticole,' 1860 p. 204, et 1867 p. 43.

[179] 'Bull. Soc. Bot. Fr.,' 1858, p. 685.

[180] The structure of this flower is discussed at some length in a paper by the author on axillary prolification. 'Trans. Linn. Soc.,' vol. xxiii, p. 486, t. liv. fig. 3. See also 'Clos. Bull. Soc. Bot. Fr.,' vol. v, 1855, p. 672. Seringe et Heyland, 'Bull. Bot.,' i, p. 8. 'Pallas Enum. Plant. Hort. Demidoff,' append, c, ic.

[181] 'Adansonia,' i, 181.

[182] 'Adansonia.' vol. iii, p. 351, tab. xii.

[183] 'Elem. Terat. Veget.,' p, 218.

[184] Masters, 'Journ. Linn. Soc.,' vol. ix, 1866, p. 334.

[185] 'Trans. Linn. Soc.,' vol. xxiv, p. 143. tab. xxiv.

[186] 'Brit. Assoc. Report,' Dundee, 1867; and Seemann's 'Journal of Botany,' 1867, p. 319, tab. lxxii, figs. B 1-9.

[187] Duval Jouve, 'Hist. Equiset. France.' 1864, p. 154.

[188] 'Flora,' t. xxiv, 1841, p. 340.

[189] Moore, 'Nature-Printed British Ferns,' 8vo edition, vol. ii. p. 135. tab. lxxxv, B, &c.



CHAPTER IV.

HETEROGAMY.

This term is here intended to apply to all those cases in which the arrangement of the sexual organs is different from what it is habitually. It is evident that in many instances there is no malformation, no monstrosity, but rather a restoration of organs habitually suppressed, a tendency towards structural completeness rather than the reverse. It must be also understood that the following remarks apply to structural points only, and are not intended to include the question of function. The occurrence of heteromorphic unions renders it necessary to keep in mind that plants hermaphrodite as to structure are by no means necessarily so as to function.

The simplest case of this alteration in the relative position of the sexes is that which occurs in monoecious plants, where the male and female flowers have a definite position, but which in exceptional instances is altered.

Change in the relative position of male and female flowers may thus occur in any monoecious plant. Cultivated maize, Zea Mays, frequently exhibits alterations of this kind; under ordinary circumstances, the male inflorescence is a compound spike, occupying the extremity of the stem, while the female flowers are borne in simple spikes at a lower level, but specimens may now and then be found where the sexes are mixed in the same inflorescence; the upper branching panicle usually containing male flowers only, under these circumstances, bears female flowers also.[190] In like manner, but less frequently, the female inflorescence occasionally produces male flowers as well.

Among the species of Carex it is a common thing for the terminal spike to consist of male flowers at the top, and female flowers at the base; the converse of this, where the female flowers are at the summit of the spike, is much more uncommon. An illustration of this occurrence is given in the figure (fig. 100). Among the Coniferae numerous instances have been recorded of the presence of male and female flowers on the same spike, thus Mr. now Professor Alexander Dickson exhibited at the Botanical Society of Edinburgh in July, 1860, some malformed cones of Abies excelsa, in which the inferior part of the axis was covered with stamens, whilst the terminal portion produced bracts and scales like an ordinary female cone. The stamens of the lower division were serially continuous with the bracts above. Some of the lower scales of the female portion were in the axils of the uppermost stamens, which last were somewhat modified, the anther cells being diminished, whilst the scale-like crest had become more elongated and pointed, in fact, more or less resembling the ordinary bracts.[191] Mohl, Schleiden, and A. Braun have observed similar cones in Pinus alba, and Cramer figures and describes androgynous cones in Larix microcarpa. C. A. Meyer ('Bull. Phys. Math.,' t. x, 1850) also describes some catkins of Alnus fruticosa which bore male flowers at the top, and female flowers at the base.



On the subject of this section the reader may consult A. Braun,. 'Das Individ.,' 1853, p. 65. Caspary, 'De Abietin. flor. fem. struct. morphol.' Schleiden. 'Principles,' English edition, p. 299. Mohl, 'Verm. Schrift.,' p. 45. Meyen in 'Wiegm. Archiv.,' 1838, p. 155. Cramer, 'Bildungsabweich,' p. 4, tab. v, figs. 13-17. Parlatore, 'Ann. Sc. Nat.,' ser. iv, vol. xvi, p. 215, tab. 13A. See also under the head of Prolification, Substitutions, &c.

Change from the monoecious to the dioecious condition.—This is of less frequent occurrence than might have been anticipated. In the 'Gardeners' Chronicle,' 1847, pp. 541 and 558, several instances are noted of walnut trees bearing female flowers to the exclusion of males. The mulberry tree has also been noticed to produce female blossoms only, while in other plants male flowers only are developed.

It seems probable that the age of the plant may have something to do with this production of flowers of one sex to the exclusion of the other.

Change from the dioecious to the monoecious condition.—Androgynism.— This is of far more common occurrence than the preceding.



In the hop (Humulus Lupulus), when monoecious, the female catkins are usually borne on the ends of the branches as shown in the cut (fig. 101), and a similar thing has been noticed in Urtica dioica by Clos, 'Bull. Soc. Bot. France,' vol. 9, p. 7.

Baillon ('Etudes du groupe des Euphorbiacees,' p. 205) mentions the following species of that order as having been seen by him with monoecious inflorescence: Schismatopera distichophylla, Mozinna peltata, Hermesia castaneifolia. Oliver mentions ('Hook. Icon. Plant.,' t. 1044) that in Leitneria floridana the upper scales of the male catkin occasionally subtend an ovary.

It would seem that external conditions have some effect in determining the formation of one sex, as in some species of Carex, while in the case of Salix repens, Hampe[192] says that when grown partially or for a time under water, those twigs which are thrust up above the surface bear female flowers, while those twigs that blossom after the water is dried up, produce male flowers only.

Carriere[193] says that a plant of Stauntonia latifolia which for some years produced stamens only, now produces flowers of both sexes; it was dioecious, but is now monoecious. The same author alludes to a similar occurrence in Juniperus Virginiana. The hops is also said to vary in sexual characteristics from time to time.[194] In addition to the genera, already named, in which this production of flowers of both sexes has been observed may be mentioned Taxus! Gunnera! Urtica! Mercurialis! Restio! Cannabis! Salix! Humulus! as well as others in which the change is less frequent.

Among cryptogams a similar change occurs. As an illustration may be cited Leucobryum giganteum, as quoted from Mueller in Henfrey's 'Botanical Gazette,' i, p. 100.

As to androgynous willows, in addition to the references given under the head of Substitution of stamens for pistils, see Schlechtendal, 'Flora Berol.,' ii. p. 259. Tausch, 'Bot. Zeit.,' 1833, i. p. 229. Koch, 'Synops. Flor. Germ.,' 740. Host, 'Flor. Aust,.' ii, p. 641 (S. mirabilis). See also Hegelmaier, 'Wuerttemberg Naturwissenshaft Jahreshefte,' 1866, p. 30. Other references to less accessible works are given in 'Linnaea,' xiv, p. 372.

Change from hermaphroditism to unisexuality.—Many flowers ordinarily hermaphrodite as to structure, become unisexual by the abortion or suppression of their stamens, or of their carpels, as the case may be. This phenomenon is lessened in interest since the demonstration of the fact by Darwin and others, that many plants, structurally hermaphrodite, require for the full and perfect performance of their functions the cooperation of the stamens and pistils, belonging to different individuals of the same species.

Some of the Ranunculaceae constantly exhibit a tendency towards the dioecious condition, and the rarity with which perfect seeds of Ranunculus Ficaria are formed is to be attributed, in great measure, to the deficiency of pollen in the anthers of these flowers. Ranunculus auricomus also is frequently sterile. Specimens of Ranunculus bulbosus may be met with in which every flower is furnished with carpels, most of which have evidently been fertilised, although there are no perfect stamens in the flowers.

Knight and other vegetable physiologists have been of opinion that a high temperature favours the production of stamens, while a lower degree of heat is considered more favorable to the production of pistils, and in this way the occurrence of "blind" strawberries has been accounted for. Mr. R. Thompson, writing on this subject, speaks of a plantation of Hautbois strawberries which in one season were wholly sterile, and accounts for the circumstance as follows: the plants were taken from the bearing beds the year previous, and were planted in a rich well-manured border, in which they started rapidly into too great luxuriance, the growth being to leaves rather than to fruit. The following season these same plants bore a most abundant crop, hence these plants were accidentally prevented from perfecting their female organs.[195]

Mr. Darwin[196] cites from various sources the following details relating to strawberries which it may be useful to insert in this place, as throwing some light upon the production of unisexual flowers. "Several English varieties, which in this country are free from any such tendency, when cultivated in rich soils under the climate of North America commonly produce plants with separate sexes. Thus, a whole acre of Keen's seedlings in the United States has been observed to be almost sterile in the absence of male flowers; but the more general rule is, that the male plants over-run the females.... The most successful cultivators in Ohio plant, for every seven rows of pistillate flowers, one row of hermaphrodites, which afford pollen for both kinds; but the hermaphrodites, owing to their expenditure in the production of pollen, bear less fruit than the female plants."

Stratiotes aloides has been said to produce its carpels with greater abundance towards the northern limits of its geographical distribution, and its stamens, on the other hand, are stated to be more frequently developed in more southern districts.

Honckenya peploides affords another illustration of the sexual arrangements in the flower being altered as it would seem by climatal conditions. Thus, in the United States, according to Professor Asa Gray, the flowers are frequently hermaphrodite, while in this country they are usually sub-dioecious.[197]

Treviranus[198] says that the flowers of Hippuris and Callitriche are apt to be hermaphrodite in summer, but female only at a later period.

For further remarks on this subject, see sections relating to suppression of stamens and pistils.

Change from unisexuality to hermaphroditism.—This occurrence depends on one of two causes, either organs are developed (stamens or pistils as the case may be), which are habitually absent in the particular flower; or some of the stamens may be more or less completely converted into or replaced by pistils, or vice versa.

The first condition is the opposite of suppression; it is, as it were, a restoration of symmetry, and might be included under the head of regular peloria, inasmuch as certain organs which habitually undergo suppression at a certain stage in their development, by exception, go on growing, and produce a perfect, instead of an imperfect flower. In teratological records it is not always stated clearly to which of the two above-named causes the unusual hermaphroditism belongs, though it is generally easy to ascertain this point. Very many, perhaps all, diclinous flowers may, under certain conditions, become perfect, at least structurally. I have myself seen hermaphrodite flowers in Cucurbita,[199] Mercurialis, Cannabis, Zea Mays, and Aucuba japonica, as well as in many Restiaceae, notably Cannamois virgata and Lepyrodia hermaphrodita. Spinacia oleracea, Rhodiola rosea, Cachrys taurica, and Empetrum nigrum are also occasionally hermaphrodite.

Gubler[200] alludes to a similar occurrence in Pistacia Lentiscus, wherein, however, he adds that there was a deficiency of pollen in the flowers.

Schnizlein[201] observed hermaphrodite flowers in the beech, Fagus sylvatica, the ovaries being smaller than usual, and the stamens epigynous.

Baillon[202] enumerates the following Euphorbiaceae as having exceptionally produced hermaphrodite flowers, Crozophora tinctoria, Suregada sp., Phyllanthus longifolius, Breynia sp., Philyra brasiliensis, Ricinus communis, Conceveiba macrophylla, Cluytia semperflorens, Wall, non Roxb. Mercurialis annua and Cleistanthus polystachyus.

In some of these cases the hermaphroditism is due to the development of anthers on the usually barren staminodes, though, in other cases, the stamens would seem to be separate, independent formations, as they do not occupy the same relative position that the ordinary stamens would do if developed.[203]



Robert Brown[204] observed stamens within the utricle of Carex acuta, and Gay is stated by Moquin ('El. Ter. Veg.,' p. 343) to have observed a similar occurrence in Carex glauca.

Paasch[205] observed a similar occurrence in C. caespitosa, and Schauer, in C. paludosa,[206] though in the latter instance the case seems to have been one of transformation or substitution rather than one of hermaphroditism.

The second cause of this pseudo-hermaphroditism is due either to the more or less perfect mutation of male and female organs, or it may be to the complete absence of one and its replacement by another, as when out of many stamens, one or more are deficient, and their places occupied by carpels. This happens very frequently in willows and poplars, and has been seen in the beech.[207]



In Begonia frigida[208] the anomaly is increased by the position of the ovaries above, the perianth, a position due, not to any solution or detachment of the latter from the former, but simply to the presence of ovaries where, under ordinary circumstances, stamens only are formed, as happened also in a garden variety of a Fuchsia, wherein, however, the change was less perfect than in the Begonia, and in which, as the flower is naturally hermaphrodite, the alteration is of the less importance.



In hermaphrodite flowers of Carica Papaya (fig. 103) there is a single row of five stamens instead of two rows of five each as in the normal male flowers, the position of the second or inner row of stamens being occupied by five carpels, which, however, are not adherent to the corolla as the stamens are, thus, supposing the arrangement of parts in the normal male flowers to be as follows:

- s s s s s - p p p p p st st st st st st st st st st

That of the hermaphrodite blossoms would be, in brief, as follows:

5 s 5 p 5 st 5 c

One of the most curious cases of this kind recorded is one mentioned by Mr. Berkeley,[209] wherein a large white-seeded gourd presented a majority of flowers in which the pollen was replaced by ovules. It would seem probable from the appearances presented by the figure that these ovules were, some of them, polliniferous, like those of the Passiflora, &c., described at p. 185, but nothing is stated on the subject.

See also section on Regular Peloria, Substitution, Pistillody of the stamens, &c.

FOOTNOTES:

[190] See also Clos., 'Mem. Acad. Toulouse,' sixth ser., t. iii, pp. 294-305. Scott, 'Trans. Bot. Soc. Edinburgh,' t. viii, p. 60. Wigand, 'Flora,' 1856, p. 707.

[191] Professor Dickson concludes from the examination of these structures that the male cone, consisting of simple stamens developed on one common axis, must be regarded as a simple male flower, while the axillary scales of the female cone are by him compared with the flattened shoots of Ruscus.

[192] 'Linnaea,' xiv, 367.

[193] Rev. Hortic.,' January, 1867.

[194] See Royle, 'Man. Materia Medica,' ed. 1, p. 567.

[195] Thomson, 'Gardener's Assistant,' p. 577.

[196] 'Variation of Animals and Plants,' i, 353.

[197] Babington, 'Ann. Nat. Hist.,' vol. ix, 1852, p. 156.

[198] 'Phys. der Gewaechse,' ii, p. 323.

[199] See also Schlechtendal, 'Linnaea,' viii, p. 623, and Lindley, 'Veg. Kingd.,' p. 315.

[200] 'Bull. Soc. Bot. France,' vol. ix, p. 81.

[201] Cited in Henfrey, 'Bot. Gazette.' 3, p. 11.

[202] Baillon. 'Etudes du Groupe des Euphorbiacees,' p. 205, tab. xv, fig. 19, tab. xix, fig. 31.

[203] See also Guillemin, 'Mem. Soc. Nat. Hist. Paris,' I, p. 16; hermaphrodite flowers in Euphorbia esula.

[204] 'Prod. Flor. N. Holl.,' p. 242.

[205] 'Bot. Zeit.,' 1837, p. 335.

[206] 'Pflanz, Terat.,' von Moquin-Tandon, p. 208.

[207] Schnizlein, loc. cit.

[208] 'Bot. Mag.,' tab. 5160, fig. 4. See also 'Gard. Chron.,' 1860, pp. 146, 170; 1861, p. 1092.

[209] 'Gard. Chron.,' 1851, p. 499.



CHAPTER V.

ALTERATIONS IN THE DIRECTION OF ORGANS.

The deviations from the ordinary direction of organs partake for the most part more of the nature of variations than of absolute malposition or displacement. It must also be borne in mind how frequently the direction of the leaves, or of the flower, varies according to the stage of development which it has arrived at, to unequal or disproportionate growth of some parts, or to the presence of some impediment either accidental or resulting from the natural growth of the plant. These and other causes tend to alter the direction of parts very materially.

Change in the direction of axile organs, roots, stems, &c.—The roots frequently exhibit good illustrations of the effect of the causes above mentioned in altering the natural direction. The roots are put out of their course by meeting with any obstacle in their way. Almost the only exception to the rule in accordance with which roots descend under natural circumstances, is that furnished by Trapa natans, the roots of which in germination are directed upwards towards the surface of the water. So in Sechium edule, the seed of which germinates while still in the fruit, the roots are necessarily, owing to the inverted position of the embryo, directed upwards in the first instance.

A downward direction of the stem or branches occurs in many weak-stemmed plants growing upon rocks or walls, or in trees with very long slender branches as in Salix Babylonica, and the condition may often be produced artificially as in the weeping ash.

The opposite change occurs in what are termed fastigiate varieties, where the branches, in place of assuming more or less of a horizontal direction, become erect and nearly parallel with the main stem as in the Lombardy poplar, which is supposed to be merely a form of the black Italian poplar.

M. de Selys-Longchamps has described a similar occurrence in another species of Poplar (P. virginiana Desf.), and amongst a number of seedling plants fastigiate varieties may frequently be found, which may be perpetuated by cuttings or grafts, or sometimes even by seed; hence the origin of fastigiate varieties of elms, oaks, thorns, chestnuts, and other plants which may be met with in the nurseries.

Sometimes when the top of the main stem is destroyed by disease or accident, one of the heretofore lateral shoots takes its place, and continues the development of the tree in the original direction. It is often an object with the gardener to restore the symmetry of an injured tree so that its beauty may ultimately not be impaired.[210]

Climate appears sometimes to have some influence on the direction of branches, thus Dr. Falconer, as quoted by Darwin,[211] relates that in the hotter parts of India "the English Ribston-pippin apple, a Himalayan oak, a Prunus and a Pyrus all assume a fastigiate or pyramidal habit, and this fact is the more interesting as a Chinese tropical species of Pyrus naturally has this habit of growth. Nevertheless many of the fastigiate varieties seen in gardens have originated in this country by variation of seeds or buds."

M. Carriere has also recorded a curious circumstance with reference to the fastigiate variety of the false acacia Robinia pseudacacia; he states that if a cutting or a graft be taken from the upper portion of the tree, the fastigiate habit will be reproduced, and the branches will be furrowed and covered with short prickles; but if the plant be multiplied by detaching portions of the root-stock, then instead of getting a pyramidal tree with erect branches, a spreading bushy shrub is produced, with more or less horizontal, cylindrical branches, destitute of prickles.[212]

Eversion of the axis.—In the case of the fig, the peculiar inflorescence is usually explained on the supposition that the termination of the axis becomes concave, during growth, bearing the true flowers in the hollow thus formed. The cavity in this case would probably be due not to any real process of excavation, but to a disproportionate growth of the outer as contrasted with the central parts of the fig. Some species of Sempervivum have a similar mode of growth, so that ultimately a kind of tube is formed, lined by the leaves, the central and innermost being the youngest. The hip of the Rose may be explained in a similar manner by the greater proportionate growth of the outer as contrasted with the central portions of the apex of the flower-stalk. In cases of median prolification, already referred to, the process is reversed, the central portions then elongate into a shoot and no cavity is formed. A fig observed by Zuccarini (figs. 105, 106) appears to have been formed in a similar manner, the flower-bearing summit of the stalk not being contracted as usual, the flowers projected beyond the orifice of the fig. If this view be correct the case would be one rather of lengthening of the axis than of absolute eversion since it was never inverted.



Altered direction of leaves.—The leaves partake more or less of the altered direction of the axis, as in fastigiate elms, but this is not universally the case, for though the stem is bent downwards the leaves may be placed in the opposite direction; thus in some specimens of Galium Aparine growing on the side of a cliff from which there had been a fall of chalk, the stems, owing apparently to the landslip, were pendent, but the leaves were abruptly bent upwards.

One of the most singular instances of an inverted direction of the leaves is that presented by a turnip (fig. 107) presented to the Museum of King's College, London, by the late Professor Edward Forbes. The turnip is hollow in the interior and the majority of the leaves springing from its apex instead of ascending into the light and air become bent downwards so as to occupy the cavity, and in such a manner as to bring to mind the position of an inverted embryo in a seed.



Altered direction of the flower and its parts.—The changes which take place in the relative position either of the flower as a whole or of its several parts during growth are well known, as also are the relations which some of these movements bear to the process of fertilisation, so that but little space need here be given to the subject beyond what is necessary to point out the frequent changes of direction which necessarily accompany various deviations from the ordinary form and arrangement of parts.

In cases where an habitually irregular flower becomes regular, the change in form is frequently associated with an alteration in direction both of the flower as a whole and, to a greater or less extent, of its individual members, for instance of Gloxinia, the normal flowers of which are irregular and pendent, there is now in common cultivation a peloriate race in which the flowers are regular in form and erect in position.



Fig. 108 shows the usual irregular form of Gloxinia, with which may be contrasted figs. 109, 110 and 111.

Fig. 109 shows the regular erect form; fig. 110 the calyx of the same flower; while in fig. 111 are shown the stamens and style of the two plants respectively. In the upper figure the style of the peloriate variety is shown as nearly straight, and the stamens undergo a corresponding change. No doubt the relative fertility and capacity for impregnation of the two varieties is affected in proportion to the change of form. The Gloxinia affords an instance of regular congenital peloria in which the regularity of form and the erect direction are due to an arrest, not of growth, but of development, in consequence of which the changes that ordinarily ensue during the progress of the flower from its juvenile to its fully formed condition do not take place.



A similar alteration accompanies this form of peloria in other flowers (see Peloria). A change in direction may result also from other circumstances than those just alluded to. Abortion or suppression of organs will induce such an alteration; thus in a flower of Pelargonium now before me three of the five carpels, from some cause or other, are abortive and much smaller than usual, and the style and the beak-like torus are bent downwards towards the stunted carpels instead of being, as they usually are, straight.

Amongst orchids, where the pedicel of the flower or the ovary is normally twisted, so that the labellum occupies the anterior or inferior part of the flower, it frequently happens, in cases of peloria and other changes, that the primitive position is retained, the twist does not take place, and so with other resupinate flowers. In Azaleas a curious deflexion of the parts of the flower may occasionally be met with. Fig. 112 shows an instance of this in which the corolla, the stamens and the style were abruptly bent downwards: as young flowers of this singular variety have not been examined it is difficult to form an opinion as to the cause of this variation. In one plant the change occurred in connection with the suppression of all the flowers but one in the cluster, or rather the place of the flowers was occupied by an equal number of leafy shoots.



Moquin[213] mentions a flower of Rosa alpina in which two of the petals were erect, while the remaining ones were much larger and expanded horizontally. The same author quotes from M. Desmoulins the case of a species of Orobanche, in which a disjunction of the petals constituting the upper lip took place, thus liberating the style and allowing it to assume a vertical direction.



M. Carriere[214] has described an instance wherein two apples were joined together, a larger and a smaller one; the former was directed away from the centre of the tree as usual, while the smaller one was pointed in exactly the opposite direction. The larger fruit had the customary parchment-like carpels, the smaller was destitute of them.

Sometimes the direction assumed by one flower as an abnormal occurrence is the same as that which is proper to an allied species or genus under natural circumstances; thus flowers of the vine (Vitis) have been met with in which the petals were spreading like a star (fleurs avalidouires), as in the genus Cissus.[215]

Morren describes a curious condition in some flowers of Cuphea miniata, in which the placenta protruded through an orifice in the ovary, and losing the horizontal direction became erect (figs. 113, 114). A similar occurrence happened in Lobelia erinus. To this condition the Belgian savant gave the name of gymnaxony.[216]

FOOTNOTES:

[210] The following details as to the method pursued by Mr. McNab, of the Edinburgh Botanic Garden, may not be uninteresting in this place. They are from the pen of Mr. Anderson, and originally appeared in the 'Gardeners' Chronicle.'

"The mode of inducing leaders to proceed from laterals is a matter of comparatively little concern among the generality of deciduous trees, for they are often provided with subsidiary branches around the leader, at an angle of elevation scarcely less perpendicular, but the laterals of all Conifers stand, as nearly as possible, at right angles. Imagine the consternation of most people when the leader of, say, Picea nobilis, P. Nordmanniana, or P. Lowii is destroyed."

In a specimen of the latter plant the leader had been mischievously destroyed, to remedy which Mr. McNab adopted means which Mr. Anderson goes on to describe. "Looking from the leader downward to the first tier of laterals, there appeared to have been a number of adventitious leaf-buds created, owing to the coronal bud being destroyed. These were allowed to plump up unmolested until the return of spring, when every one was scarified or rubbed off but the one nearest the extremity. To assist its development and restrain the action of the numerous laterals, every one was cut back in autumn, and this restraint upon the sap acted so favorably upon the incipient leader as to give it the strength and stamina of the original leader, so that nothing detrimental was evident twelve months after the accident had happened, and only a practical eye could detect that there had been any mishap at all. This beautifully simple process saved the baby tree.

"Another example of retrieving lost leaders may be quoted as illustrative of many in similar circumstances. Picea Webbiana had its leader completely destroyed down to the first tier of laterals. There was no such provision left for inducing leaf-buds as was the case with P. Lowii above referred to. Resort must, therefore, be had to one of the best favoured laterals, but how is it to be coaxed from the horizontal position of a lateral to the perpendicular position of a leader? The uninitiated in these matters, and, in fact, practical gardeners generally, would at once reply, by supporting to a stake with the all-powerful Cuba or bast-matting. But no. A far simpler method than that, namely, by fore-shortening all the laterals of the upper tier but the one selected for a leader. Nature becomes the handmaid of art here; for without the slightest prop the lateral gradually raises itself erect, and takes the place of the lost leader. All that the operator requires to attend to is the amputation of the laterals until this adventitious fellow has gained a supremacy. Singular provision in nature this, which, thanks to the undivided attention of a careful observer, has been fully appreciated and utilized."