FOOTNOTES:

Fig.166.—Portion of the under surface of a cabbage-leaf, with horn-like excrescences projecting from it.

Formation of tubes.—The production of ascidia or pitchers from the cohesion of the margins of one or more leaves has been already alluded to (see pp. 21,30), but there is another class of cases in which the tubular formation is due, not so much to the union of the margins of a leaf as to the disproportionate growth of some portions as contrasted with others, whence arises either a depressed cavity, as in the case of a leaf, oran expanded and excavated structure, when the stem or some portion of it is affected.

The fruit of the rose, the apple, the fig, and many others, is now generally admitted to be composed externally of the dilated end of the flower-stalk in which the true carpels become imbedded. Between such cases and that of a peltate leaf with a depressed centre, such as often occurs, to some extent, inNelumbium, there is but little difference.

In cabbages and lettuces there not unfrequently occurs a production of leaf-like processes projecting from the primary blade at a right angle (see Enation). Sometimes these are developed in a tubular form, so as to form a series of little horn-like tubes, or shallow troughs, as inAristolochia sipho. At other times the nerves or ribs of the leaf project beyond the blade, and bear at their extremities structures similar to those just described.

Fig.167.—Lettuce leaf, bearing on the back a stalked cup, arising from the dilatation of the stalk (?).

In a variety ofCodiæum variegatuma similar formation may be seen to a minor extent. Even the commonScolopendrium vulgareoccasionally produces small pitchers of this character, as in the varieties namedperafero-corautum, Moore, andperaferum, Woll.[350]

In carnations leaves may sometimes be seen from both surfaces, from which project long, sharp-pointed tubular spurs at irregular intervals. A very singular illustration of this is figured by Trattinick,[351], in which the leaves, epicalyx, sepals, and petals, were all provided with tubular spurs.

InCephalotus follicularisrudimentary or imperfect pitchers may be frequently met with, in which the stalk of the leaf is tubular and bears at its extremity a very small rudimentary leaf-blade. It is not in all cases easy to trace the origin and true nature of the ascidium, as the venation is sometimes obscure. If there be a single well-marked midrib the probability is that the case is one of cohesion of the margins of the leaf; but if the veins are all of about equal size, and radiate from a common stalk, the pouch-like formation is probably due to dilatation and hollowing of the petiole. Again, when the result of a union of the margins of the leaf, the pitcher is generally less regular than when formed from the hollowed end of a leaf-stalk. Further information is especially needed as to the mode of development and formation of these tubular organs, so as to ascertain clearly when they are the result of a true cupping process, and when of cohesion of the margins of one or more leaves. (See Cohesion, p. 31. For bibliographical references consult also A. Braun, 'Flora v. Bot. Zeit.,' 1835, t. xviii, p. 41,Aristolochia.)

Tubular formations in the flower.—A similar formation of tubes happens in some double flowers; for instance, it is not infrequent in double flowers ofPrimula sinensis, in which tubular petal-like structures areattached to the inner surface of the corolla; sometimes these petaloid tubes replace the stamens, while at other times they appear to have no relation to those organs. In the particular flowers now alluded to the tubular form seems due to a dilatation, and not to a cohesion of the margins. (See Cohesion, p. 23.) These tubular petals resemble in form and colour almost precisely the normal corolla in miniature, but are not surrounded by a calyx, nor do they contain stamens, while the less perfect forms show clearly their origin from a single tube-like organ.

Fig.168.—Corolla ofPrimula sinensisturned back to show a tubular petal springing from it. One only is shown for the sake of clearness; they are generally numerous.

The formation of spurs or spur-like tubes in a quasi-regular manner has been spoken of under the head of Irregular Peloria, p. 228, but we occasionally meet with tubular processes which seem to occur in an irregular manner, and to have no reference to the symmetrical plan of the flower, and which are due probably to the same causes as those which induce hypertrophy. Such spurs have frequently been seen on the corolla ofDigitalis purpurea,Antirrhinum majus,[352]Tulipa Gesneriana, and occasionally on the sepals ofFuchsia. They are very frequent in some seasons in the corolla of certain calceolarias (C. floribunda). By Morren this production of adventitious spurs was called "Ceratomanie."

Fig.169.—Corolla ofCalceolaria, showing irregular tubular spurs projecting from the lower lip.

Similar processes may sometimes be seen in the capsules ofLinaria vulgaris, as also in the fruits of some of the Solanums, quite without reference to the arrangement of the carpels, so that their production seems to be purely irregular.

Morren, as previously remarked, gave the name "Solenaidie" to tubular deformities affecting the stamens, a term which has not been generally adopted; the deformity in question is by no means of uncommon occurrence in some double or partially pelorised flowers, asAntirrhinum,Linaria, &c. A similar formation of conical out-growths may frequently be met with in the fruits quite irrespectively of any disjunction of the carpels.

Contortion.—An irregular twisting or bending of the stem or branches is by no means of uncommon occurrence, the inducing causes being often some restriction to growth in certain directions, or the undue or disproportionate growth in one direction, as contrasted with that in another. Hence it may arise from insect-puncture, parasitic growth, or any obstacle to the natural development. Frequently it exists in conjunction with fasciation, the ends of the branches being curved round like a shepherd's crook, from the growth on one side being so much greater than on the other. Sometimes it is a mere exaggeration of a normal condition; thus, in what are termed flexuose stems the stem twists alternately to one side or another, frequently in associationwith an oblique form of the leaf. This state is sometimes present to an extreme degree, as in some varieties of shrubs (Cratægus,Robinia, &c.) cultivated for their singularly tortuous branches.

Fig.170.—Portion of the culm of aJuncus, bent irregularly.

Fig.171.—Portion of a branch ofCratægus oxyacantha, var.tortuosa.

Such cases as those just mentioned, however, are but slightly irregular compared to others in which the deformity exists to such an extent that the traces of the ordinary mode of growth are almost obliterated.M. Moquin-Tandon[353]alludes to a case of this kind in a species of pine (Pinus), in which a branch ended in four unequal divisions, which were strongly curved from without inwards, then became united in pairs, these latter in their turn blending into a single mass.

In the case of some beeches growing in the forest of Verzy, near Rheims, the trunks of the trees are contorted in every direction, and, at a height of from fifteen to twenty feet, a number of branches are also given off, also much contorted, and occasionally intergrafted, so that it seems as if a heavy weight had been placed on the trees and literally flattened them. Similar malformations may occasionally be met with in the branches of the oak, and commonly in the weeping ash.

M. Fournier[354]mentions the stems ofRuscus aculeatusrolled in a circle, others twisted spirally.

The phenomenon is not confined to woody plants, but has been met with in chicory, inAntirrhinum, and other herbaceous species.

It is very difficult in some cases to separate these instances of irregular torsion from those in which the twisting takes place in a more or less regular spiral direction. In the former case the fibres of the plant are only indirectly involved, but in the latter the fibres themselves are coiled spirally from right to left, orvice versâ(spiral torsion), while not unfrequently both conditions may be met with at the same time.

The leaves also are subject to similar deformities, of which a notable illustration has been recorded in the case of the date palm,Phœnix dactylifera, originally observed by Goethe, and figured and described by Jaeger;[355]the leaves are folded and twisted in every direction, in consequence of the fibrous band or cord which surrounds the leaves, and which generally breaksas the leaflets increase in size, remaining from some cause or other unbroken, and thus serving to restrain the growth.

A similar irregularity of growth occurs, not unfrequently, in the case of crocus leaves, when in the course of their growth, as they push their way through the soil, their progress becomes checked either by a stone or even by frost.

Spiral torsion.—Growth in a spiral direction, and the arrangement of the various organs of the plant in a spiral manner, are among the most common of natural phenomena in plants.[356]Fibres are coiled spirally in the minute vessels of flowering plants, and are not wholly wanting even among fungi. The leaf-organs are very generally spirally arranged; the leaf-stalks are often so twisted as to bring leaves on one plane which otherwise would occupy several. In the leaf itself we have a spiral twist taking place constantly inAlstrœmeria, inAvena, and other plants. A similar tendency is manifested in the flower-stalks, as inCyclamenandVallisneria, and the whole inflorescence, as inSpiranthes. Even the bark and wood of trees is often disposed spirally. This is very noticeable in some firs, and in the bark of the sweet chestnut (Castanea), ofThuja occidentalis, and other trees. The knaurs or excrescences which are sometimes found on the roots or stems of trees afford other illustrations of this universal tendency. These bodies consist of a number of embryo buds, which, from some cause or other, are incapable of lengthening. On examination every rudimentary or undeveloped bud may be seen to be surrounded by densely crowded fibres arranged spirally.

The axes of nearly all twining plants are themselves twisted, and twisted in a direction corresponding to the spontaneous revolving movement exhibited by these plants, as in the hop, the convolvulus, passion flower,&c., the degree of twisting being dependent to a great extent on the roughness of the surface around which the stem twines[357].

Considered as an exceptional occurrence, it occurs frequently in certain plants, and, when it affects the stem or branches, necessarily causes some changes in the arrangement of the parts attached to them; thus, spiral torsion of the axial organs is generally accompanied by displacement of the leaves, whorled leaves becoming alternate, and opposite or whorled leaves becoming arranged on one side of the stem only. Frequently also this condition is associated with fasciation, or, at least, with a distended or dilated state. An illustration of this inAsparagushas been figured at p. 14.

Very often the leaves are produced in a spiral line round the stem, as in a specimen ofDracocephalum speciosumdescribed and figured by C. Morren. The leaves of this plant are naturally rectiserial and decussate, but, in the twisted stem the leaves were curviserial, and arranged according to the 5/13 plan. Now, referring to the ordinary notation of alternate leaves, we shall have the first leaf covered by the fifth, with two turns of the spiral; since decussate leaves result from two conjugate lines, the formula will be necessarily 2/5. The fraction 5/13 hence comes regularly into the 2/5 series (2/5, 3/8, 5/13). Thus, the leaves in assuming a new phyllotaxy, take one quite analogous to the normal one.

One of the most curious instances that have fallen under the writer's own observation occurred in the stem ofDipsacus fullonum. (See 'Proceedings ofthe Linnean Society,' March 6, 1855, vol. ii, p. 370). The stem was distended, and hollow, and twisted on itself; its fibres, moreover, were arranged in an oblique or spiral direction; the branches or leaf-stalks, which usually are arranged in an opposite and decussate manner, were, in this case, disposed in a linear series, one over the other, following the line of curvature of the stem. When the course of the fibres was traced from the base of one of the stalks, upward around the stem, a spiral was found to be completed at the base of the second stalk, above that which was made the starting point. Now, if opposite leaves depend on the shortened condition of the internode between the two leaves, then, in the teazel-stem just described, each turn of the spiral would represent a lengthened internode; and, if the fibres of this specimen could be untwisted, and made to assume the vertical direction, and, at the same time, the internodes were shortened, the result would be the opposition of the branches and the decussation of the pairs; this explanation is borne out by the similar twisting which takes place so frequently in the species ofGaliumand otherRubiaceæ.

Fig.172.—Twisted stem ofDipsacus fullonum.

G. Franc[358]was one of the first to notice this twisting inGalium, and M. Duchartre,[359]in mentioning a similar instance, gives the following explanation of the appearance which will be found to apply to most of these cases. In the normal stem ofGalium Mollugothe branchesare opposite in each verticil and crossed in the two successive ones. The stem is four-angled, each angle having a nerve. Each of these nerves, springing from the origin of a branch in one whorl, terminates in the interval which separates the point of origin of the two branches in the whorl next above it. In the deformed stem one of the nerves corresponds to the insertion of a branch, its neighbour is in the adjoining vacant space; hence it results that four nerves correspond to two branches and to two consecutive interspaces, and hence the analogy between a single normal internode provided with its two branches and its four nerves. What confirms this inference is that the nerve, which begins at the point of origin of a branch, after making one spiral turn round the stem, terminates in the interval that separates the two following branches, just as in a branch of the normal stem it ends in the upper whorl between the two next branches. The torsion, then, in thisGaliumcaused the separation of the two opposite branches of the same verticil, and placed them one above another, and this being reproduced in all the whorls, all the branches come to be arranged on the same longitudinal line. The leaves are susceptible of the same explanation; they are inserted in groups of three or four in one arc round the origin of each branch. In the malformation each series or group of four leaves, with its central branch, is equivalent to half a whorl of the natural plant with its axillary branch. In other words, the malformation consists in a torsion of the stem, which separates each whorl into two distinct halves; these half-whorls, with their axillary branches, are placed on a single longitudinal series one above another. This case is quoted at some length, as it is an admirable example of a very common form of malformation in these plants.

In some parts of Holland where madder is cultivated a similar deformation is particularly frequent. The leaves, however, are not always grouped in the way in which they were described by M. Duchartre,but more commonly form a single continuous line; when arranged in leaf-whorls it generally happens that some of the leaves are turned downwards, while others are erect. It has been said that this condition occurs particularly frequently in plants growing in damp places. It is certainly true that spiral torsion of the stem is specially frequent in the species ofEquisetum, most of which grow in such spots. In these plants either the whole of the upper part of the stem is thus twisted, or a portion only: thus Reinsch[360]cites a case inEquisetum Telmateia, where the upper and lower portions of the stem were normal, while the intermediate portion was twisted spirally. In this instance the whorl next beneath the spiral had twenty-eight branchlets, and that immediately above it thirty. Along the course of the spire there were two hundred and three; dividing this latter number by the mean ofthe two preceding, it was seen that the spire included the constituents of seven ordinary verticils.

Fig.173.—Stem ofGaliumspirally twisted. From a specimen communicated by Mr. Darwin.

Here also may be mentioned a curious bamboo, the stem of which is preserved in the British Museum, and in which the internodes, on the exterior, and the corresponding diaphragms and cavities within are spiral or oblique in direction.

The root is also subject to the same malformation, the inducing cause being usually some obstruction to downward growth, as when a plant has been grown in a small pot, and becomes, as gardeners say, pot-bound.

Fig.174.—Showing "pot-bound" root twisted spirally (from the 'Gard. Chron.,' 1849).

The axial portion of the flower, the thalamus, is also occasionally twisted in a spiral direction, the lateral parts of the flower being in consequence displaced.Morren spoke of this displacement of the floral organs as "speiranthie."[361]

Morren draws a distinction between spiral-torsion or spiralism and the less regular torsion spoken of in the preceding section; in the former case not only is the axis twisted, but its constituent fibres also. The condition in question in some cases seems to be inherited in the seedling plants.

The following is a list of the plants in which spiral torsion of the stem or branches has been most frequently observed. (See also under Fasciation and Contortion.)

Hesperis matronalis.Dianthus barbatus.Pyrus Malus.torminalis.Cercis siliquastrum!Punica Granatum.Robinia pseudacacia!Rubia tinctorum.Dipsacus fullonum!pilosus.Gmelini.Scabiosa arvensis.*Valeriana officinalis!dioica!Galium aparine!*Mollugo!verum!Hippuris vulgaris!Veronica spicata.longifolia.Hyssopus officinalis.Thymus Serpyllum.Lamium purpureum!Dracocephalum speciosum.Mentha aquatica.Mentha viridis.Fraxinus vulgaris!Sambucus nigra.Zinnia.Phylica.Beta.Rumex, sp.Ulmus campestris.Casuarina rigida.Abies excelsa!Lilium Martagon!candidum.*Asparagus officinalis!Sagittaria sagittifolia.Epipactis palustris.Triticum repens!Lolium perenne!Phleum pratense.Juncus conglomeratus!Scirpus lacustris.Equisetum Telmateia.limosum.fluviatile.arvense!

Among the more important papers relating to this subject may be mentioned:

Moquin-Tandon, 'El. Ter. Veg.,' p. 181. Kros, 'De Spira in plantis conspicua.' Morren, 'Bull. Acad. Roy. Belg.,' 1851, tom. xviii, part i, p. 27. Milde, 'Nov. Act. Acad. Leop. Carol. Nat. Cur., 1839. Ibid., vol. xxvi, part ii, p. 429,Equisetum. Irmisch, 'Flora,' 1858, t. ii,Equisetum. Vrolik, 'Nouv. Mem. Instit. Amsterdam,'Lilium. Schlechtendal, 'Bot. Zeit.,' xiv, p. 69, et v, p. 66. De Candolle, 'Organ.Veget., t. i, p. 155, tab. xxxvi,Mentha,&c.Alph. de Candolle, 'Neue Denkschr. Allg. Schweiz. Gesellschft.,' band v, tab. vi,Valeriana. Duchartre, 'Ann. Sc. Nat.,' ser. 3, vol. i, p. 292. 'Gardeners' Chronicle,' July 5, 1856, p. 452,c. ic. xylogr., spiral branches from Guatemala—tree not known.

Spiral twisting of the leafis scarcely of so common occurrence as the corresponding condition in the stem. InAlstrœmeriait occurs normally, as also in some grasses. In the varietyannularisofSalix babylonicathe leaf is constantly coiled round spirally. A similar contortion occurs in a variety ofCodiæum variegatumlately introduced from the islands of the South Seas by Mr. J. G. Veitch.

Fern fronds are occasionally found twisted in the same manner,e.g.Scolopendrium vulgarevar.spirale.[362]

Adventitious tendrils.—Under ordinary circumstances tendrils may be described as modifications of the leaf, the stipule, the branch, or of the flower stalk, so that it is not a matter of surprise to find tendrils occasionally springing from the sepals or petals, as indeed happens normally inHodgsonia,Strophanthus,&c.

M. Decaisne[363]found a flower of the melon in which one of the segments of the calyx was prolonged into a tendril, and Kirschleger records a similar instance in the cucumber, while Mr. Holland ('Science Gossip,' 1865, p. 105) mentions a case in which one of the prickles on the fruit of a cucumber had grown out into a tendril.

InCobæa scandensthe foliar nature of the tendril is shown by the occasional presence of a small leaflet on one of the branches of the tendril, and a similar appearance may frequently be seen inEccremocarpus scaber. On the other hand, in the vine, the axial nature of the tendril is revealed by the not infrequent presence of flowers or berries on them, as also inModeccaand somePassifloraceæ.

Darwin, speaking of the tendrils ofBignonia capreolata, says it is a highly remarkable fact that a leaf should be metamorphosed into a branched organ, which turns from the light, and which can, by its extremities, either crawl like a root into crevices, or seize hold of minute projecting points, these extremities subsequently forming cellular masses, which envelope by their growth the first fibres and secrete an adhesive cement.

Interrupted growth.—This term is here used in the same sense as in ordinary descriptive botany, as when an "interruptedly pinnate" leaf is spoken of. A similar alternation may be observed occasionally as a teratological occurrence, though it is not easy to account for it.

Fig.175.—Interrupted growth of Radish (from the 'American Agriculturist.')

Fig.176.—Interrupted growth in Apple.

Fig. 175 shows an instance of the kind in a radish, and fig. 176 a similar deformity in the case of an apple, the dilatation of the flower-stalk below the ordinary fruit producing an appearance as if there were two fruits one above another.

In leaves this peculiar irregularity of development is more common.

In some varieties ofCodiæum variegatumthe leaves resemble those ofNepenthes, as the basal portion is broad, and terminates in a projecting midrib destitute of cellular covering, and this again terminates in a small pouch or pitcher. Somewhat similar variations may be found in ferns, especiallyScolopendrium vulgare.

Instead of the pouch there is formed sometimes in the plant last mentioned a supplementary four-lobed lamina, the four lobes being in two different planes, and diverging from the midrib, so that the section would resemble [symbol: Sideways X], the point of intersection of the x representing the position of the midrib. This four-winged lamina is thus very similar to the four-winged filaments described and figured at p. 289, and to the leaf-like anther ofJatrophadescribed by M. Müller, p. 255.

Cornute leaves(Folia cornuta).—The condition to which this term applies is that in which the midrib, after running for a certain distance, generally nearly to the point of the leaf, suddenly projects, often in a plane different from that of the leaf, and thus forms a small spine-like out-growth. Should this happen to be terminated by a second laminar portion, an interrupted leaf would be formed. InScolopendrium vulgareand other ferns this condition has been noticed, as also in some of the varieties ofCodiæum variegatumalready referred to.

Flattening.—There are some plants whose stem or branches, instead of assuming the ordinary cylindrical form, are compressed or flattened; such are some species ofEpiphyllum,Coccoloba,Bauhinia, &c. The same thing occurs in the leaf-like branches ofRuscus, the flower-stalks ofXylophylla,Phyllanthus,Pterisanthes. Martins proposes to apply the word 'cladodium' to such expansions, just as the term phyllodium is applied to the similar dilatation of the leaf-stalks. If we excludeinstances of fasciation,i.e.where several branches are fused together and flattened, we must admit that this flattening does not occur very often as a teratological appearance.

Mr. Rennie figures and describes a root of a tree which had become greatly flattened in its passage between the stones at the bottom of a stream, and had become, as it were, moulded to the stones with which it came into contact.[364]

The spadix ofArum, as also of the cocoa-nut palm, has been observed flattened out, apparently without increase in the number of organs.

When the blade of the leaf is suppressed it often happens that the stalk of the leaf is flattened, as it were, by compensation, and the petiole has then much the appearance of a flat ribbon (phyllode). This happens constantly in certain species ofAcacia,Oxalis, &c., and has been attributed, but doubtless erroneously, to the fusion of the leaflets in an early state of development and in the position of rest.[365]

In some water plants, asSagittaria,Alisma,Potamogeton, &c., the leaf-stalks are apt to get flattened out into ribbon-like bodies; and Olivier has figured and described aCyclamen, called by himC. linearifolium, in which, owing to the suppression of the lamina, the petiole had become dilated into a ribbon-like expansion—déformation rubanée of Moquin.

FOOTNOTES:[350]Moore, 'Nature Printed Ferns,' 8vo edition, vol. ii, p. 154, et p. 173.[351]'Flora (B. Z.),' 1821, vol. iv, p. 717, c. tab.[352]Chavannes, 'Mon. Antirrh.'[353]'Bull. Soc. Bot. France,' t. vii, 1860, p. 877.[354]Ibid., t. iv, 1857, p. 759.[355]Jaeger, "De monstrosa foliiPhœnicis dactyliferæconformatione a Goetheo olim observata," 'Act. Acad. Leop. Car. Nat. Cur.,' vol. xvii, suppl., p. 293, c. tab. color. iv.[356]See Goethe, 'Ueber die spiral Tendenz.'[357]See Darwin "On Climbing Plants," 'Journ. Linn. Soc. Botany,' vol. ix, p. 5.[358]'Ephem. Nat. Cur.,' dec. 2, ann. 1, 1683, p. 68, fig. 14.[359]'Ann. des Scienc. Nat.,' third series, vol. i, 1844, p. 292.[360]'Flora' Feb. 4, 1858, p. 69, tab. ii, f. 3, and also 'Flora,' 1860, p. 737, tab. vii, f. 9.[361]'Bull. Acad, Belg.,' t. xvii, p. 196, "Lobelia," p. 53, c. tab.[362]Moore, 'Nature-printed Ferns,' 8vo edition, vol. ii, p. 183.[363]'Bull. Soc. Bot. Fr.,' 1860, vol. vii, p. 461. See also Naudin, 'Ann. Sc. Nat.,' 4 ser., t. iv, p. 5. Clos, 'Bull. Soc. Bot. Fr.,' t. iii, p. 546.[364]London's 'Magazine Nat. Hist.,' vol. ii, p. 463.[365]C. Morren, 'Bull. Acad. Belg.,' 1852, t. xix, part iii, p. 444.

[350]Moore, 'Nature Printed Ferns,' 8vo edition, vol. ii, p. 154, et p. 173.

[351]'Flora (B. Z.),' 1821, vol. iv, p. 717, c. tab.

[352]Chavannes, 'Mon. Antirrh.'

[353]'Bull. Soc. Bot. France,' t. vii, 1860, p. 877.

[354]Ibid., t. iv, 1857, p. 759.

[355]Jaeger, "De monstrosa foliiPhœnicis dactyliferæconformatione a Goetheo olim observata," 'Act. Acad. Leop. Car. Nat. Cur.,' vol. xvii, suppl., p. 293, c. tab. color. iv.

[356]See Goethe, 'Ueber die spiral Tendenz.'

[357]See Darwin "On Climbing Plants," 'Journ. Linn. Soc. Botany,' vol. ix, p. 5.

[358]'Ephem. Nat. Cur.,' dec. 2, ann. 1, 1683, p. 68, fig. 14.

[359]'Ann. des Scienc. Nat.,' third series, vol. i, 1844, p. 292.

[360]'Flora' Feb. 4, 1858, p. 69, tab. ii, f. 3, and also 'Flora,' 1860, p. 737, tab. vii, f. 9.

[361]'Bull. Acad, Belg.,' t. xvii, p. 196, "Lobelia," p. 53, c. tab.

[362]Moore, 'Nature-printed Ferns,' 8vo edition, vol. ii, p. 183.

[363]'Bull. Soc. Bot. Fr.,' 1860, vol. vii, p. 461. See also Naudin, 'Ann. Sc. Nat.,' 4 ser., t. iv, p. 5. Clos, 'Bull. Soc. Bot. Fr.,' t. iii, p. 546.

[364]London's 'Magazine Nat. Hist.,' vol. ii, p. 463.

[365]C. Morren, 'Bull. Acad. Belg.,' 1852, t. xix, part iii, p. 444.

Usually the several organs of the same individual plant do not differ to any great extent one from another. One adult leaf has nearly the same appearance anddimensions as another; one flower resembles very closely another flower of the same age and so on. Nevertheless it occasionally happens that there is a very considerable difference in form in the same organs, not only at different times, but it may also be at the same time. Descriptive botanists recognise this occurrence in the case of leaves, and apply the epithet heterophyllous to plants possessed of these variable foliar characters. In the case of the flower, where similar diversity of form occasionally exists, the term dimorphism is used.

As these phenomena appear constantly in particular plants, they are hardly to be looked on, under such circumstances, as abnormal, but where they occur in plants not usually polymorphic, they may be considered as coming within the scope of teratology.

Heterophylly.—As a general rule, the leaves or leaf-organs in each portion of a plant, from the rhizome or underground axis, where it exists, to the carpellary leaf, have their own special configuration, subject only to slight variations, dependent upon age, conditions of growth, &c. The cotyledons are very uniform in shape in each plant, and are scarcely ever subject to variation. The leaves near the base of the stem, the root-leaves as they are not unfrequently called, sometimes differ in form from the stem-leaves; these again differ from the bracts or leaves in proximity to the flower. The floral envelopes themselves, as well as the bud-scales, all have their own allotted form in particular plants, a form by which they may, in most cases, be readily recognised. Hence, then, in the majority of plants there is naturally very considerable difference in the form of the leaf-organs, according to the place they occupy and the functions they have to fulfil; but, in addition to this, it not unfrequently happens that the leaf-organs in the same portion of the stem are subject to great variation in form. This is the condition to which the term heterophylly properly applies. The variation in form is usuallydependent on a greater or less degree of lobing of the margin of the leaf; thus, in the yellow jasmine, almost every intermediate stage may be traced from an ovate entire leaf to one very deeply and irregularly stalked.Broussonettia papyrifera, andLaurus Sassafras, and the species ofPanax, may be mentioned as presenting this condition. Sometimes in the last-named genus, as also inPteridophyllum, every gradation between simple and compound leaves may be traced. The horse-radish (Cochlearia Armoracia) may also be instanced as a common illustration of polymorphism inthe leaves. In ferns it is likewise of frequent occurrence, markedly so inScolopendrium D'Urvillei, in which plant every gradation from a simple oblong frond to an exceedingly divided one may be found springing from the same rhizome at the same time.

Fig.177.—Syringa persica laciniata, showing polymorphous leaves.

A similar protean state, but little less remarkable, occurs in many of our British ferns, notably inScolopendrium vulgare, of which Mr. Moore enumerates no fewer than 155 varieties,[366]many of the forms occurring on the same plant at the same time. Cultivators have availed themselves of this tendency to produce multiform foliage, not only for the purposes of decoration or curiosity, as in the many cut-leaved or crisped-leaved varieties, but also for more material uses, as, for instance, the many varieties of cabbages, of lettuces, &c. Most of these variations are mentioned under the head of the particular morphological change of which they are illustrations.

The effect of a change in the conditions of growth in producing diversity in the form of the leaf may be here alluded to.Ficus stipulata, a plant used to cover the walls of plant-stoves in this country, and growing naturally on walls in India, like ivy, produces leaves of very different form, size, and texture, when grown as a standard, from what it does when adhering to a wall.Marcgraavia umbellatafurnishes another example of a similar nature, as indeed, to a less extent, does the common ivy.

Allusion has been already made to the occasional persistence of forms in adult life, which are commonly confined to a young state, as in the case of some conifers which present on the same plant, at the same time, two different forms of leaves. Mention has also been made of the presence of adventitious buds on leaves and in other situations. The leaves that spring from these buds are usually of the same form as the other leaves of the plant, but now and then they differ. Of this a remarkable illustration is afforded by a fern,Pteris quadriaurita, in which the fronds emerging from an adventitious bud are very different from the ordinary fronds.

Fig.178.—Portion of a frond ofPteris quadriaurita, with an adventitious bud, the form of the constituent foliage of which is very different from that of the parent frond.

Dimorphism.—This term, applied specially to the varied form which the flowers or some of their constituent elements assume on the same plant, is an analogous phenomenon to what has been above spoken of as heterophylly, and, like it, it cannot, except under special circumstances, be considered as of teratological importance. A few illustrative cases, however, may here be cited.

Sir George Mackenzie describes a variety of the potato[367](Solanum tuberosum), which produces first double and sterile flowers, and subsequently single fertile ones; the other portions of the plant do not differ much.

Stackhousia juncea, according to Clarke, has mixed with its perfect flowers a number of apetalous blossoms destitute of anthers.[368]

This peculiarity is well exemplified in the tribeGaudichaudieæof the orderMalpighiaceæ. A. de Jussieu, in his monograph, speaks of these flowers as being very small, green, destitute of petals, or nearly so, with a single, generally imperfect anther; the carpels also are more or less imperfect, but not sufficiently so to prevent some seeds from being formed. A similar production of imperfect flowers has been noticed in many other orders,e.g.Violaceæ,Campanulaceæ, &c. In some cases these supplementary blossoms are more fertile and prolific in good seeds than are the normally constructed flowers. M. Durieu de Maisonneuve alludes to a case where flowers of this description are produced below the surface of the ground. The plant in question isScrophularia arguta, and it appears that towards the end of the summer the lowest branches springing from the stem bend downwards, and penetrate the soil; the branches immediately above the lowest ones also bend downwards, but do not always enter the earth. These branches bear fertile flowers: those which are completely below the soil are completely destitute of petals; those which are on the surface have a four-lobed corolla whose divisions are nearly equal, like those ofVeronica.[369]

To Sprengel, and specially to Darwin, physiologists are indebted for the demonstration of the relation of di- and trimorphic flowers to fertilisation. In certain genera of orchids, such asCatasetum, &c., flowers of such different form are produced that botanists, without hesitation, considered them as belonging to different genera, until the fact of their occasional production on the same plant showed that they were not of even specific importance. It was reserved for Mr. Darwin to show experimentally that these very different flowersare really sexual forms of one and the same species, ordinarily occurring on different plants, i.e. diœcious, but occasionally formed on the same spike. The same excellent observer has demonstrated that the di- and trimorphic forms ofPrimula, ofLinum,Lythrum, and other plants—forms differing mainly in the relative length of the stamens and styles, are also connected with striking differences in the number of perfect seeds produced. The most perfect degree of fertility is obtained when the stigma of one form is fertilised by the pollen taken from stamens of a corresponding height. On the other hand, when the union is, as Mr. Darwin states, illegitimate, that is, when the pollen is taken from stamens not corresponding in length to the style, more or less complete sterility ensues in the progeny, sometimes even utter infertility, such as happens when two distinct species are crossed, so that, in point of fact, the offspring of these illegitimate unions correspond almost precisely to hybrids.[370]

Mere variations of form arising from hybridisation or other causes hardly fall within the limits of this work, though it is quite impossible to say where variations end and malformations begin. There are, however, two or three cases cited by Mr. Darwin[371]from Gallesio and Risso to which it is desirable to allude. Gallesio impregnated an orange with pollen from a lemon, and the fruit borne on the mother tree had a raised stripe of peel like that of a lemon both in colour and taste, but the pulp was like that of an orange, and included only imperfect seeds. Risso describes a variety of the common orange which produces "rounded-oval leaves, spotted with yellow, borne on petioles, with heart-shaped wings; when these leaves fall off they are succeeded by longer and narrower leaves, with undulated margins, of a pale green colour, embroidered with yellow, borne on foot-stalks withoutwings. The fruit whilst young is pear-shaped, yellow, longitudinally striated and sweet; but, as it ripens, it becomes spherical, of a reddish-yellow, and bitter."

Sports or bud variations.—These curious departures from the normal form can only be mentioned incidentally in this place, as they pertain more to variation than to malformation.

The occasional production of shoots bearing leaves, flowers, or fruits of a different character from those found on the normal plant, is a fact of which gardeners have largely availed themselves in the cultivation of new varieties. The productions in question have been attributed to various causes, such as cross-breeding, grafting, budding, dissociation of hybrid characters, or reversion to some ancestral form, all of which explanations may be true in certain cases, but none of them supply the clue to the reason why one particular branch should be so affected, and the rest not; or why the same plant, at the same time, as often happens in Pelargoniums, should produce two, three, or more "sports" of a different character.

These bud variations may be perpetuated by grafts or by cuttings, sometimes even by seed. With reference to cuttings a curious circumstance has been observed, viz., that if taken from the lower part of the stem, near the root, the peculiarity is not transmitted, but the young plant reverts to the characters of the typical form (Carrière). This circumstance, however, is not of universal occurrence.

For further particulars on this interesting subject the reader is referred to Darwin's 'Variation of Animals and Plants,' i, p. 373, where numerous references are given, and wherein certain well-known and highly remarkable instances, such as theCytisus Adami, the trifacial orange, &c., are discussed.

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