MALFORMATION (from Lat. mains, had + formatio, formation, from formare. to shape, front forma, shape). The abnormal process which gives rise to an organ or whole plant whose form is strikingly different from the ordi nary; by metonymy, the organ or plant itself, also called a monstrosity. The term malforma tion is applied most properly to a grotesque form. and particularly to one in which the de parture from the normal is apparently unre lated to its function. The term ceeidiUm has been proposed to include galls and malformations, the cause . being indicated by prefixes. That branch of biological science which deals with mal formations is known as teratology.
The distinction between malformations and variations is Almost all cul tivated plants have been brought to their present state of perfection by cumulative selection, the desired variations being fixed by proper breeding until a race has been developed. The organs in these cultivated races, however, differ from those of the wild original oftentimes far more than do those aberrant terms which are called malforma tions. The one, however, has arisen slowly by gradations; the other has appeared suddenly.
Suddenness of origin, therefore, is one of the criteria of umlformation. Malformations may be due to any local disturbance of the usual course of growth and development; for instance, local or general disease. Local disease is often produced by the presence of either an animal or a plant parasite, which produces malformations known as galls. Other malformations are due either to the action of external conditions, such as light and moisture, or to causes which, being entirely unknown, are assumed to be internal.
Little has as yet been done in the experimental study of malformations, but since plant organs are remarkably plastic, it is scarcely to be doubted that the spe cific action of exter nal agents will yet be demonstrated. ln very few cases, how ever, can explanation of the origin of mal formations be given at present. There is no question that, having once occurred, mal formations may be transmitted to t he offspring. Horticul turists are familiar with many instances of this. Malforma tions are known in all groups of plants. es pecially among the larger ferns and seed plants. Nearly 4000 species in these two groups have produced monstrosities which have been described. Only a few of the more important classes of deviation from the normal can be men- • tioncd.
( 1 ) For unknown reasons organs may entirely fail to appear, or they may be arrested in a very young state, so that they do not become evident, or they may be dwarfed by stoppage of growth when partially developed. All sible gradations occur between organs of normal • size and those that are completely suppressed.
(2) Hypertrophy.—From equally unknown causes an organ may develop to an dinary size without undergoing any noteworthy change in form. It is common to ascribe trophy to an excessive supply of food, but other stimuli must certainly operate. Young shoots of heavily pruned trees, or suckers from the stems, often have all organs immensely larged. (3) Concrescence is a term applied to the actual union of parts in the course of their development. Such unions are not common, most of the eases of apparent being explicable in an entirely different fashion. Thus the ent union of flower parts is due to the growth of a ring of tissue underneath the developing separate rudiments, carrying these upward on the edge of a growing cup or cylinder. (See FLOWER.) Actual union is due to the adhesion of young surface cells of organs which are closely crowded as they are forming. The union is seldom firm, and slight pressure suf fices to separate the adherent parts with out real tearing. (4) Fasciat ion.— Stems, normally cylindrical, sometimes develop in a flattened form, sev eral to many times the ordinary diam eter in one direction and not unusually thickened in the other. (Fig. 1.) Not infrequently one edge of this broad stem grows more rapidly than the other. when it becomes curved edgewise, crosier-like. The ridges and grooves on the surface suggest the union of several normal steins. Con trary to appearance. however, such stems are not ordinarily due to congenital union of independent stems. each from a single bud, but are produced by the simultaneous development of several buds in line. Fasciation is very common in rapidly growing stems, which are abundantly supplied with food and water. The young shoots of asparagus, the flower stalks (scapes) of the dandelion, and young shoots from severely pruned trees frequently furnish fine examples. (5) Sobrtion.—In most seed plants some of the foliar or floral structures are ordinarily developed in circles or whorls or in a crowded spiral. If nowhere else, this is certain to occur in the flow ers. (Fig. 2.) Sometimes the stem develops between the points of attachment of these nor mally crowded leaves, separating them unusually. Thus it comes that flower leaves are sometimes separated by consider able lengths of stem and the flower loses acteristic form. Not in frequently at the same time the petals lose their brighter hues and become greenish. ( 6 ) Proliferation is a con tinued growth of an axis whose growth is normally finished. or the development of a branch from growing points which ordinarily either are not formed at all or remain dormant.