Vegetable Teratology / An Account of the Principal Deviations from the Usual Construction of Plants

by Maxwell T. Masters

The plan followed in this volume is a slight modification of that adopted by Moquin-Tandon, and with several additions. In it the aim is to place before the student certain salient and easily recognisable points by reference to which the desired information can readily be found. Under each subdivision will be found general explanatory remarks, illustrative details, and usually a summary of the more important facts and the inferences to be derived from them. Bibliographical references and lists of the plants most frequently affected with particular malformations are also given. In reference to both these points it must be remembered that absolute completeness is not aimed at; had such fullness of detail been possible of attainment it would have necessitated for its publication a much larger volume than the present.[5] It is hoped that both the lists of books and of plants are sufficiently full for all general purposes.[6]

In the enumeration of plants affected with various malformations the ! denotes that the writer has himself seen examples of the deviation in question in the particular plant named, while the prefix of the * indicates that the malformation occurs with special frequency in the particular plant to which the sign is attached.

Teratological alterations are rarely isolated phenomena, far more generally they are associated with other and often compensatory changes. Hence it is often necessary, in studying any given malformation, to refer to two or more subdivisions, and in this way a certain amount of repetition becomes unavoidable. The details of the several cases of malformation given in these pages are generally arranged according to their apparent degree of importance. Thus, in a case of prolification associated with multiplication of the petals, the former change is a greater deviation from the customary form than the latter, hence reference should be made, in the first instance, to the sections treating on prolification, and afterwards to those on multiplication. To facilitate such research, numerous cross references are supplied.

In the investigation of teratological phenomena constant reference must be made to the normal condition, and vice versâ, else neither the one nor the other can be thoroughly understood. It cannot, however, be overlooked that the form and arrangement called normal are often merely those which are the most common, while the abnormal or unusual arrangement is often more in consonance with that considered to be typical than the ordinary one. Thus, too, it is often found that the structural arrangements, which in one flower are normal, are in another abnormal, in so far that they are not usual in that particular instance.

For purposes of reference, a standard of comparison is required; and this standard, so long as its nature is not overlooked, may, indeed must be, to some extent, an arbitrary one. Thus in the phanerogamous plants there is assumed to exist, in all cases, an axis (stem, branches, roots, thalamus, &c.), bearing leaves and flowers. These latter consist of four whorls, calyx, corolla, stamens, and pistils, each whorl consisting of so many separate pieces in determinate position and numbers, and of regular proportionate size. A very close approach to such a flower occurs normally in Limnanthes and Crassula, and, indeed, in a large proportion of all flowers in an early stage of development. To a standard type, such as just mentioned, all the varied forms that are met with, either in normal or abnormal morphology, may be referred by bearing in mind the different modifications and adaptations that the organs have to undergo in the course of their development. Some parts after a time may cease to grow, others may grow in an inordinate degree, and so on; and thus, great as may be the ultimate divergences from the assumed standard, they may all readily be explained by the operation, simply or conjointly, of some of the four principal causes of malformation before alluded to. The fact that so many and such varied changes can thus readily be explained is not only a matter of convenience, but may be taken as evidence that the standard of reference is not wholly arbitrary and artificial, but that it is a close approximation to the truth.

It has already been said that an arrangement like that here considered as typical is natural to some flowers in their adult state, and to a vast number in their immature condition. It would be no extravagant hypothesis to surmise that this was the primitive structure of the flower in the higher plants. Variations from it may have arisen in course of time, owing to the action of an inherent tendency to vary, or from external circumstances and varied requirements which may have induced corresponding adaptations, and which may have been transmitted in accordance with the principle of hereditary transmission. This hypothesis necessarily implies a prior simplicity of organisation, of which, indeed, there is sufficient proof; many cases of malformation can thus be considered as so many reversions to the ancestral form.

Thus, teratology often serves as an aid in the study of morphology in general, and also in that of special groups of plants, and hence may even be of assistance in the determination of affinities. In any case the data supplied by teratology require to be used with caution and in conjunction with those derived from the study of development and from analogy. It is even possible that some malformations, especially when they acquire a permanent nature and become capable of reproducing themselves by seed, may be the starting-point of new species, as they assuredly are of new races, and between a race and a species he would be a bold man who would undertake to draw a hard and fast line.[7]

Discredit has been cast on teratology because it has been incautiously used. At one time it was made to prove almost everything; what wonder that by some, now-a-days, it is held to prove nothing. True the evidence it affords is sometimes negative, often conflicting, but it is so rather from imperfect interpretation than from any intrinsic worthlessness. If misused the fault lies with the disciple, not with Nature.

Teratology as a guide to the solution of morphological problems has been especially disparaged in contrast with organogeny, but unfairly so. There is no reason to exalt or to disparage either at the expense of the other. Both should receive the attention they demand. The study of development shows the primitive condition and gradual evolution of parts in any given individual or species; it carries us back some stages further in the history of particular organisms, but so also does teratology. Many cases of arrest of development show the mode of growth and evolution more distinctly, and with much greater ease to the observer, than does the investigation of the evolution of organs under natural circumstances. Organogeny by no means necessarily, or always, gives us an insight into the principles regulating the construction of flowers in general. It gives us no archetype except in those comparatively rare cases where primordial symmetry and regularity exist. When an explanation of the irregularity of development in these early stages of the plant's history is required, recourse must be had to the inferences and deductions drawn from teratological investigations and from the comparative study of allied forms precisely as in the case of adult flowers.

The study of development is of the highest importance in the examination of plants as individuals, but in regard to comparative anatomy and morphology, and specially in its relation to the study of vegetable homology it has no superiority over teratology. Those who hold the contrary opinion do so, apparently, because they overlook the fact that there is no distinction, save of degree, to be drawn between the laws regulating normal organisation, and those by which so-called abnormal formations are regulated.