Vegetable Teratology Part 28

BOOK II.

DEVIATIONS FROM THE ORDINARY FORM OF ORGANS.

In a morphological point of view the form of the various parts or organs of plants and the changes to which they are subjected during their development are only second in importance to the diversities of arrangement and, indeed, in some cases, do not in any degree hold a second place.

Taken together, the arrangement, form, and number of the several parts of the flower, make up what has been termed the symmetry of the flower.[217] Referring to the a.s.sumed standard of comparison, see p. 4, it will be seen that in the typically regular flower all the various organs are supposed to be regular in their dimensions and form. At one time it was even supposed that all flowers, no matter how irregular they subsequently became, began by being strictly symmetrical or regular, and that subsequent alterations were produced by inequality of growth or development. The researches of organogenists have, however, dispelled this idea of unvarying primordial regularity, by showing that in many cases flowers are irregular from the very first, that some begin by being irregular, and subsequently become regular, and even in some cases resume their original condition during the course of their development.[218] Under these circ.u.mstances an artificial standard of comparison becomes almost an absolute necessity for the time being.

Changes of form very generally, but not always, are accompanied with a change in regularity: thus a flower habitually bi-lateral may a.s.sume the characters of radiating symmetry and _vice versa_. Increase or decrease of size very frequently also are co-existent with an alteration in the usual form.

In the case of the arrangement of organs it is often difficult or impossible, in the present state of our knowledge, to determine whether a given arrangement is congenital or acquired subsequently to the first development, whether for instance an isolation of parts be due to primordial separation or to a subsequent disunion of originally combined organs, see p. 58. With reference to the changes in the form of organs, however, it is in general more easy to ascertain the proximate cause of the appearance, and thus teratological changes of form may be grouped according as they are due to, 1, arrest of development; 2, undue or excessive development; 3, perverted development; and 4, irregular development; hence the use of the following terms--Stasimorphy, Pleiomorphy, Metamorphy, and Heteromorphy--to include teratological changes really or apparently due to one or other of the causes above mentioned. The cla.s.sification here adopted is of course to a considerable extent an arbitrary one and subject to correction or modification, as the knowledge of the development of the flowers in the various genera of plants advances.

FOOTNOTES:

[217] The word symmetry has been used in very different senses by different botanists, sometimes as synonymous with "regularity," at other times to express the a.s.sumed typical form of a flower. Payer understands it to be that arrangement of parts which permits of the whole flower being divided vertically into two symmetrical halves (bi-lateral symmetry). Others, again, have applied the term symmetry to the number of the parts of the flower, reserving the terms "regularity" or "irregularity" for the form. It is here used in a general sense to express the plan of the flower, and thus includes the arrangement, form, and number of its component elements.

[218] See Baillon, 'Adansonia,' v, 176.

PART I.

STASIMORPHY.[219]

Deviations from the ordinary form of organs arising from stasis or arrest of development are included under this heading.

There are many cases in which the forms proper to a juvenile condition of the plant are retained for a much longer period than ordinary, or even throughout the life of the individual growth goes on, but "development" is checked. Such conditions may even be propagated by seed or bud. It is a very general thing for botanists to consider these cases as reversions to a simpler, primitive type, and this may be so; but on the other hand, they may be degenerations from a complex type, or they may have no direct relation to any antecedent condition. Stasimorphic changes affecting princ.i.p.ally the relative size of organs--such, for instance, as the non-development of internodes, or the atrophy or suppression of parts will be found mentioned in the sections relating to those subjects. In the present part those alterations which affect the form of organs princ.i.p.ally are treated of.

FOOTNOTES:

[219] [Greek: Stasis-morphosis].

CHAPTER I.

PERSISTENCE OF JUVENILE FORMS.

The retention in adult life of a form characteristic of an early stage of development, and therefore usually transient, may be manifested in any of the organs of the plant. As these cases are for the most part treated under separate headings, it is here only necessary to allude to a few, which it is difficult to allocate satisfactorily, while the reader may be referred for other instances of like nature to the sections on Peloria, Atrophy, Suppression, Dimorphy, Subst.i.tutions, &c.

[Ill.u.s.tration: FIG. 115.--_Juniperus sinensis_. Two forms of leaves on branches of the same shrub.]

=Stasimorphy in the leaves of conifers.=--In many conifers the leaves produced in the young state of the plant are different, both in arrangement and form, from those subsequently developed (see pp. 89, 90). But it occasionally happens that the plant continues to form throughout its existence leaves such as are usually produced only in a young state; thus M. Gubler ('Bull. Soc. Bot., Fr.,' vol. viii, 1861, p.

527) describes a plant of _Pinus pinea_ in which the primordial, usually transitory, foliage was permanent, leaves of the ordinary shape not being developed at all. It more often happens that some only of the leaves retain their young form while others a.s.sume other shapes, see fig. 115. This happens frequently in the larch and constantly in the Chinese juniper when it has arrived at a considerable age. In _Cupressus funebris_ two forms of leaves may often be found on the same plant, the one representing the juvenile state, the other the more developed condition. What is very singular, is that a cutting taken from the branch with leaves of the young form grows up into a shrub bearing leaves of no other shape, so that an ordinary observer unacquainted with the history of the plant would imagine that he had to deal with two distinct species. This fact is the more interesting when compared with the alternation of generations which takes place among the lower animals.

The regular development of all the parts of the flower in a plant habitually producing irregular flowers is referred to under the head of Peloria, but it still remains to consider those examples in which some only of the parts of the flower are affected in this manner.[220] Most of these cases are elsewhere referred to in this volume under the particular form of malformation a.s.sumed; but the following case may here be noticed as not coming under any of the previous heads. It is an instance recorded by Professor Babington ('Phytologist,' August, 1853), and in which the pod of _Medicago maculata_, which is usually rolled up like a snail sh.e.l.l and provided with spines, was sickle-shaped and unarmed.

FOOTNOTES:

[220] See a paper of Professor C. Morren's on "Floral Stesomy" in 'Bull.

Acad. Belg.,' t. xix, part ii, p. 519.

CHAPTER II.

REGULAR PELORIA.

[Ill.u.s.tration: FIG. 116.--Regular Peloria, _Delphinium_.]

[Ill.u.s.tration: FIG. 117.--Sepal, petal, &c., of regular-flowered _Delphinium_.]

[Ill.u.s.tration: FIG. 118--Regular peloria, _Viola_.]

[Ill.u.s.tration: FIG. 119--Double Violet, flower regular, petals multiplied, stamens and pistils petaloid.]

When an habitually irregular flower becomes regular, it does so in one of two ways; either by the non-development of the irregular portions, or by the formation of irregular parts in increased number, so that the symmetry of the flower is rendered perfect, as in the original peloria of Linnaeus, and which may be called irregular peloria, while the former case may be called regular peloria. This latter appearance is therefore congenital, and due to an arrest of development.[221] As the true nature of these cases has not been in all cases recognised (even Moquin places them under the head of deformities--they being less ent.i.tled to rank in that cla.s.s than are the usual flowers), it may be well to cite a few instances taken from various families. In _Delphinium peregrinum_ I have met with perfectly regular flowers having five sepals and five oblong stalked petals, and a similar occurrence has been noted in other species of this genus. Baillon,[222] in referring to these flowers, points out the resemblance that they bear to the double varieties of _Nigella_. In the stellate columbines (_Aquilegia_) of gardens the tubular petals are replaced by flat ones often in increased numbers. In violets both forms of peloria occur, that in which there is an unusual number of spurs, and that in which there are no spurs (var. anectaria).

In the more perfect forms of regular peloria occurring in the last-named genus the following changes may be noticed: 1, an alteration in the direction of the flower so that it remains in an erect position, and is not bent downwards as usual; 2, equality of proportion in the sepals and petals; 3, absence of spurs, as also of hairs on the lateral petals; 4, equal stamens whose anthers are sometimes entirely dest.i.tute of the prolonged crest which forms so prominent a feature under ordinary circ.u.mstances; 5, erect, not curved styles, and the stigmas not prolonged into a beak, but having a more or less capitate form; ovary with three or five cells, ovules normal.

These are cases where the change in question is most strongly marked, the bi-lateral is completely replaced by the radiating symmetry. The absence of the usual nectary, and of hairs on the side petals, the alterations in the form of the style, etc., all show how much the process of fertilisation must be altered from that which occurs under ordinary circ.u.mstances. In some of the double violets now cultivated in gardens, a similar regularity of proportion in the parts of the flower may be seen combined with the subst.i.tution of petals for stamens and pistils, and with the development of an increased number of petal-like organs.[223] Between these cases and the ordinary spurred forms as well as those with an increased number of spurs, many intermediate forms may be met with. That such regularity should occur in this family is not to be wondered at seeing that there is a whole subdivision of the order (_Alsodeiae_) in which regular flowers are the rule.

In cultivated Pelargoniums the central flower of the umbel or "truss"

frequently retains its regularity of proportion, so as closely to approximate to the normal condition in the allied genus _Geranium_; this resemblance is rendered greater by the fact that, under such circ.u.mstances, the patches of darker colour characteristic of the ordinary flower are completely wanting; the flower is as uniform in colour as in shape. Even the nectary which is adherent to the upper surface of the pedicel in the normal flower disappears--sometimes completely, at other tunes partially. The direction of the stamens and style, and even that of the whole flower, becomes altered from the inclined to the vertical position. In addition to these changes, which are those most commonly met with, the number of the parts of the flower is sometimes augmented, and a tendency to pa.s.s from the verticillate to the spiral arrangement manifested. Schlechtendal mentions some flowers of _Tropaeolum majus_ in which the flowers were perfectly regular and devoid of spurs[224], while in the double varieties, now commonly grown in greenhouses, the condition of parts is precisely the same as in the double violet before alluded to. Among the _Papilionaceae_ the Laburnum and others have been noticed to produce occasionally a perfectly regular flower in the centre, or at the extremity of the inflorescence, though the peloria in this flower is usually irregular. In the Gentianaceous genus _Halenia_, _H. heterantha_ is remarkable for the absence of spurs.

Amongst _Gesneraceae_, _Bignoniaceae_, _Scrophulariaceae_, and other families of like structure, regular peloria is not uncommon. Fig. 120 represents a case of this kind in _Eccremocarpus scaber_, conjoined, as is frequently the case, with dialysis or separation of the petals.[225]

Many of the cultivated Gloxinias also show erect, regular, five stamened flowers, but these are probably cases of irregular peloria.

[Ill.u.s.tration: FIG. 120.--Regular peloria, _Eccremocarpus scaber_.]

A solitary flower of _Pedicularis sylvatica_ was found by the Marquis of Stafford near Dunrobin Castle in Sutherlandshire, in which the usual ringent form of the corolla was replaced by the form called salver-shaped. There were six stamens, four long and two short. Sir W.

Hooker and Mr. Borrer are stated to have found a similar flower in the same locality in 1809.[226]

The pa.s.sage of ligulate to tubular corollas among _Compositae_ is not of such common occurrence as is the converse change. I owe to Mr. Berkeley the communication of a capitulum of a species of _Bidens_, in which there was a transition from the form of ligulate corollas to those that were deeply divided into three, four, or five oblong lobes. These then were instances of regular peloria.

[Ill.u.s.tration: FIG. 121.--Flower of _Cattleya marginata_. Lip replaced by a flat petal.]

In _Orchidaceae_ a similar change is not by any means infrequent; in a few, indeed, a regular flower is the normal character, as in _Dendrobium normale_, _Oncidium heteranthum_, _Thelymitra_, etc. Fig.

121, reduced from a cut in the 'Gardeners' Chronicle,' 1854, p. 804, represents an instance of this kind in _Cattleya marginata_.

From the same journal the following account of a case of peloria in _Phalaenopsis Schilleriana_ is also cited as a good ill.u.s.tration of this peculiar change. The terminal flower differed entirely from all the others; instead of the peculiar labellum there were three petals all exactly alike, and three sepals also exactly alike; the petals resembled those of the other flowers of the spike, and the upper sepal also; but the two lower sepals had no spots, and were not reflexed as in the ordinary way: thus, these six parts of the flower were all in one plane, and being close together at their edges, made almost a full round flower; the column and pollen-glands were unaffected. Professor Reichenbach also exhibited at the Amsterdam Botanical Congress, of 1865, a flower of _Selenipedium caudatum_ with a flat lip.