[140] 'Linnaea,' vol. xv, p. 266, _c. ic._ Caspary, 'Schriften d.

Physik.-Oek. Gesell. zu Konigsberg,' 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 cla.s.sed under the preceding or under other headings. The term heterotaxy is intended to apply to the production of organs in situations where, under usual circ.u.mstances, they would not be formed. It thus does not include cases of subst.i.tution, 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 advent.i.tious 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 advent.i.tious roots on the stem of the vine is considered to be due to untoward circ.u.mstances 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 circ.u.mstance 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 advent.i.tious 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 s.p.a.ce, 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 b.u.t.tresses 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 quant.i.ties, not only of advent.i.tious buds, but of roots also.

[Ill.u.s.tration: FIG. 71.--Production of advent.i.tious roots from leaf stalk of celery.]

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."

[Ill.u.s.tration: FIG. 72.--Germinating plant of mango, showing production of roots from one of the cotyledons (from the Kew Museum).]

The production of advent.i.tious 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 cretic.u.m_ and _Carum Bulbocastanum_.[148] I have figured and described an a.n.a.logous case in the cotyledons of the Mango (fig. 72).[149]

To this formation of advent.i.tious 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.

[Ill.u.s.tration: FIGS. 73 and 74 show formation of roots from leaves induced by the art of the gardener.]

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 advent.i.tious 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 a.s.sistant,' pp. 374, _et seq._; and any of the ordinary botanical text-books.

=Formation of advent.i.tious 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 circ.u.mstances, and in certain plants, e.g., _Pyrus j.a.ponica_, _Anemone j.a.ponica_, &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 advent.i.tious 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 pa.s.sing 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]

=Advent.i.tious 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 cla.s.s 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).

[Ill.u.s.tration: FIG. 75.--Leaf proceeding from hip of the Rose.]

[Ill.u.s.tration: FIG. 76.--Leaves proceeding from the ovary of _Nymphaea_.]

For other ill.u.s.trations of increased leaf-formation, see Multiplication of foliar organs.

[Ill.u.s.tration: FIG. 77.--_Leontodon_. Scape with two leaves; the bracts of the involucre are also leafy.]

=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 dest.i.tute of them, without any metamorphosis or subst.i.tution, and without any formation of advent.i.tious 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 a.n.a.logous 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, _Taraxac.u.m_, sometimes offers an ill.u.s.tration 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 circ.u.mstances, 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 pa.s.sage 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 cla.s.s of cases wherein there is a complete subst.i.tution 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.

[Ill.u.s.tration: FIG. 78.--Tuft of leaves replacing the inflorescence in a species of _Valeriana_.]

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 a.n.a.logous 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 acc.u.mulations 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 circ.u.mstances 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.