PART III.

METAMORPHY.

Much of the objection with which Goethe's famous essay on the 'Metamorphosis of Plants' was met on its publication may be traced to a misapprehension of the sense in which Goethe employed the word. As used by him, it had nearly the same signification as now applied to the word development by organogenists. It does not necessarily imply that there has been a change in any particular organ, but rather that there has been, to some extent, a change in the plan of construction, in accordance with which a deviation from the customary form results. The particular organ was never anything else than what it is; it has not been metamorphosed in the ordinary sense of the word; for instance, in a double flower, where the stamens are, as it is said, changed or metamorphosed into petals, no absolute change really has taken place--the petal was never a stamen, although it occupies the position of the latter, and may be considered a subst.i.tute for it.

The term metamorphosis, then, really implies an alteration in the organizing force, taking effect at a very early period of the life of the flower, at or before the period when the primitive aggregation of cells, of which it is at that time composed, becomes separated or "differentiated" into the several parts of the flower. In other words, the "development" of the flower pursues a different course from what is usual. In the preceding sections the effects of arrest and of excess in this process have been partly treated of; other deviations arising from similar causes will be mentioned elsewhere, but, under the present heading, are specially included cases not of merely diminished or increased, but of perverted development; the natural process is here not necessarily checked or enhanced, but it is changed. Hence, in the present work, the term metamorphy is employed to distinguish cases where the ordinary course of development has been perverted or changed. As it is applied solely for teratological purposes, the ordinary acceptation of the term, as nearly synonymous with "development," is not interfered with.

In order to avoid other possible misapprehensions, the terms retrograde and progressive metamorphosis employed by Goethe are not herein used, their place being, to a great extent, supplied by the more intelligible expressions arrest or excess of development.[244]

FOOTNOTES:

[244] See Goethe, 'Versuch. der Metam. der Pflanzen,' 1790. English translation by Emily M. c.o.x, in Seemann's 'Journal of Botany,' vol. i, 1863, p. 327. For a brief sketch of the origin and progress of the theory of vegetable morphology, prior to the publications of Wolff, Linne, and Goethe, as well as for an attempt to show what share each of these authors had in the establishment of the doctrine, the reader is referred to an article in the 'Brit. and For. Medico-Chirurgical Review,' January, 1862, ent.i.tled "Vegetable Morphology: its History and Present Condition," by Maxwell T. Masters.

CHAPTER I.

PHYLLODY.

This condition, wherein true leaves are subst.i.tuted for some other organs,[245] must be distinguished from Virescence, q. v., in which the parts affected have simply the green colour of leaves, without their form or structure. The appearance of perfect leaves, in place of other organs, is frequently looked on as due to retrograde metamorphosis, or to an arrest of development. But this is not strictly correct; for instance, suppose a petal, which is very generally merely the sheath of a leaf, with the addition of colouring matter, to be replaced by a perfect leaf, one in which all three const.i.tuent parts, sheath, stalk, and blade, are present, it surely can hardly be said that there has been any retrogression or arrest of development in the formation of a complete in place of an incomplete organ. The term retrograde here is used in a purely theoretical sense, and cannot be held to imply any actual degradation. Morphologically, as has been stated, the case is one of advance rather than the reverse, and hence the a.s.signment of instances of this nature to a perversion of development, rather than to a diminution or to an exaltation of that process, seems most consistent with truth. The affected organs have really undergone no actual change, simply the direction of the organising force has been altered at a very early state, so that the usual differentiation of parts has not taken place.

[Ill.u.s.tration: FIG. 126.--'Rose plantain,' _Plantago media var._, spike contracted; bracts leafy.]

=Phyllody of the bracts.=--As bracts are very generally imperfect organs, so their replacement by perfect leaves is not attributable to arrest of development or retrograde metamorphosis, but the reverse. The bracts of some species of _Plantago_[246] are very subject to this change. Thus, in the rose plantain of gardens, _P. media_ (fig. 126), the bracts are leafy and the axis depressed or not elongated, so that it is surmounted by a rosette of small leafy organs. A similar condition of the bracts, unattended with arrest of growth in the axis, is common in _P. major_ (fig. 127) and in _P. lanceolata_ (see p. 108). It also occurs in the bracts of _Corydalis solida_, _Amorpha fruticosa_, _Ajuga reptans_, _Parthenium inodorum_, _Centaurea Jacea_, in the involucral bracts of the dandelion, the daisy, and many other composites. In the 'Gardeners Chronicle,' 1852, p. 579, is figured a dahlia in which the bracts of the involucre and the scales of the receptacle had all a.s.sumed the form, texture, and venation of leaves.[247]

[Ill.u.s.tration: FIG. 127.--Leaf-like bracts in _Plantago major_.]

[Ill.u.s.tration: FIG. 128.--Dahlia. Scales of receptacle leafy.]

In _Umbelliferae_ the subst.i.tution of leaves for involucral bracts is not infrequent. It has been observed among other plants in _Angelica Razoulzii_, _Carum carui_, _Daucus Carota_, &c. The scales of the hop (_Humulus Lupulus_) not infrequently manifest this change, as do also the bracts of many amentaceous plants, _e.g._ in the male catkins of the walnut, the female catkins of the alder,[248] of some willows,[249]

&c. The bracts of some _Euphorbiaceae_, as _E. pusilla_, _E. Lathyris_, _E. Cyparissias_, have been observed to undergo a similar alteration.[250]

Amongst monocotyledons an a.n.a.logous change occurs not unfrequently, as in some commelynaceous plants, _e.g._ _Tradescantia_, in _Musa_, &c.

The spathe of _Arum maculatum_ is sometimes represented by a stalked leaf similar to that which occurs, under ordinary circ.u.mstances, in _Spathiphyllum_, but in which genus the spadix is more or less adherent to the leaf-like spathe.[251] In _Schoenus cephalotes_ a similar exaggerated development of the bracts is figured by Rottboell.[252]

=Phyllody in inflorescence of Conifers.=--This demands pa.s.sing notice by reason of the interest attaching to the morphological construction of these plants. The elongation of the axis which occurs in the female cones has been already alluded to under the head of prolification of the inflorescence. This change is frequently a.s.sociated with a more or less foliaceous condition of the bracts, which, indeed, may be seen to be serially continuous, both above and below, with the ordinary leaves. The scales, too, become notched and bipart.i.te, and show, between the lobes, the rudiment of a bud, which in a further stage becomes developed into a shoot bearing leaves. Such a change has been described by Parlatore in _Abies Brunoniana_, and examples may frequently be met with in the larch (_Larix europaea_), and specially in _Cryptomeria j.a.ponica_.[253] The scales of the male catkins of conifers likewise occasionally a.s.sume the appearance of leaves; this may be seen in monstrous catkins of _Araucaria_, as also in _Podocarpeae_ and _Cupressineae_ (Eichler).

=Phyllody of the calyx.=--Sepals under ordinary circ.u.mstances are so like leaves, that it is not wonderful that they are often replaced by those organs.[254] A singular instance of this has been mentioned as occurring in _Cakile maritima_, wherein the sepals were found by M.

Fournier to be pinnatifid like the ordinary leaves of the plant.[255]

The sepals of _Ranunculaceae_ and _Rosaceae_, for example, _Rosa_, _Geum_, are particularly liable to this change.

[Ill.u.s.tration: FIG. 129.--Flower of rose, sepals replaced by five perfect leaves; axis prolonged through the flower in the form of a leafy branch.]

In a species of _Geranium_ recently examined the sepals presented themselves in the form of three-lobed leaflets; so in fuchsias and in _Epilobium hirsutum_ the sepals occasionally are not distinguishable from ordinary leaves (fig. 130). In roses, the change in question is a very frequent accompaniment of prolification (fig. 129). In the peach also this replacement of the sepals is sometimes carried to such an extent, that five perfect, bistipulate leaves occur in the place of the calyx, but when this is the case it usually happens that the pistil is abortive.

[Ill.u.s.tration: FIG. 130.--Fuchsia, with one of the sepals leaf-like.]

De Candolle[256] figures a curious instance wherein the pappus of _Podospermum laciniatum_ was replaced by five linear, foliaceous lobes.

A similar change has been noticed in other composites, as in _Tragopogon pratense_. Engelmann mentions as subject to this hypertrophy of the pappus, as it may be termed, _Scorzonera octangularis_ and _Senecio vulgaris_. Wigand has observed a similar transformation in a species of _Centranthus_ (_Valerianaceae_).

In some cases the phyllody of the sepals has a special interest, as bearing on the question whether what is termed calyx-tube is or is not a portion of the calyx, and whether the sepals are modifications of the blade or of the sheath of the leaf. Thus in the primrose the phyllodic sepals seem to show clearly that the sepals are in that plant of a laminar nature (fig. 131). The so-called calyx-tube of roses is elsewhere alluded to. The leaf-like organs sometimes seen at the apex of a cuc.u.mber would seem to support the view that there was really a calyx-tube in _Cucurbitaceae_ adherent to the carpels. It is also shown in the cut, fig. 132, borrowed from the 'Gardeners' Chronicle,' 1859, p. 654.

[Ill.u.s.tration: FIG. 131.--Primrose. Calyx of foliaceous segments.]

[Ill.u.s.tration: FIG. 132.--Leafy calyx of melon.]

Under ordinary circ.u.mstances, the sepals may be considered as the representatives of the sheath of the leaf (cataphyllary) or of the blade (euphyllary), the arrangement of the veins being different in the two cases; thus, in the v.a.g.i.n.a or sheath, there are generally several large veins of about equal size, either convergent towards the apex, or divergent; on the other hand, in the blade, there is usually but one central vein, the midrib, larger than the rest, and the smaller veins come off at a less acute angle, and are more reticulated.[257]

Now, when phyllomorphy occurs in sepals which ordinarily are v.a.g.i.n.al, it is obvious that the case is one, not merely of increased relative growth, but also of the appearance or development of an organ habitually suppressed; on the other hand, when phyllomorphy occurs in sepals which usually are laminar in form and nervation, the case is one of unusual growth or hypertrophy, and not of the development of an organ habitually suppressed, so that the amount of change is greater in the former than in the latter instance.

Under normal circ.u.mstances it will be found that laminar venation is most common in gamosepalous and v.a.g.i.n.al venation in polysepalous calyces. And the same holds good in cases where the calyx is abnormally leafy. The complete leaf development shows itself more frequently among the monosepalous plants than in the polysepalous ones, as shown even in the subjoined list of species. This statement would be more fully verified were it possible to state the frequency with which the condition occurred in _individual plants_, when it would be found that phyllody of the calyx occurs much more often in individual gamosepalous plants than in polysepalous ones.

Phyllody of the calyx has been most often observed in the following plants:

Ranunculus acris!

Delphinium Ajacis.

Caltha pal.u.s.tris.

Anemone Pulsatilla.

sylvestris!

nemorosa!

hortensis!

coronaria!

*Papaver orientale.

Escholtzia crocea.

Cakile maritima.

Diplotaxis tenuifolia.

Thlaspi arvense.

Cheiranthus Cheiri.

inca.n.u.s.

Sinapis arvensis.

Bra.s.sica oleracea!

Peltaria alliacea.

*Sisymbrium officinale.

Caryophyllaceae,[258] sp. pl.

Geranium, sp.!

*Fuchsia, var. hort.!

Epilobium hirsutum!

Cucurbita Pepo!

*Rosa, var. hort.!

Potentilla nepalensis.

Fragaria sp.

Geum rivale.

Amygdalus communis.