Thus the formation of a flower usually checks the terminal growth of the axis on which it oc curs, but in the pear and apple it not infre quently resumes its growth after the fruit has begun to form and develops a leafy twig be yond it. (Fig. 3.) In a similar way. a flower cluster, such as the head in asters and sun flowers, ordinarily checks the growth of the axis, but occasionally it is prolonged through the cluster, leaving it surrounding the stem. While branches ordinarily occur in the axils of foliage leaves, they do not usually develop in the axils of floral leaves. This may occur, however, and a short branch bearing a complete flower may arise in the axil of each petal or sepal. (Fig. 4.) Some double flowers are made extra-double by this sort of proliferation. A form of prolifera tion in the flower, when the branches show a tendency to separate readily from the parent, to develop roots, or to become bulb-like and repro duce the plant readily, is called vivipary (q.v.). ( 1 Torsion.—St ems normally straight, or leaves normally flat. may through more extensive growth of one part or another be twisted or crinkled. Lettuce leaves show a erispate form on a large scale (Fig. 6) and twisted stems are extreme ly common. (S) Abnormal branching of leaves is not infrequent. Clover leaves, normally with three leaf lets (branches), are often found with four or five. or even as many as seven. The leaves of the dahlia. hickory ( Fig. 7) , and ninny other plants show similar deviations from the normal. Abnormally re peated branching in flower clusters is also common (Fig. S). (9) Pcloria. —irregular flowers, that is, those in which some parts arc larger or of a different shape from the others, sometimes develop all the parts of like form and size. Thus the yellow-and-orange flower of 'hut ter-and-eggs' or 'toad-flax' has usual ly one spurred petal; but not infrequently all live of the peta Is become spurred, and the flower is then radially symmetrical. (Fig. 5.) A similar but reverse change occurs when flow ers which are radially symmetrical become un symmetrical, as when the tubular ray flowers of the wild chrysanthemum or aster develop lignlate corollas. This is quite as monstrous a form as the opposite, but has not been in cluded among malformations. ( 10) Transfor mation of floral vats is extremely common.
are a widely known instance. (11) Pleintomery, i.e. increase in the number of any group of or Thus sepals, normally green, may grow into petal-like form and color; while petals may take the shape and function of stamens and pis tils. Transformation of this sort, that is, from a less specialized into a more specialized organ, is not so frequent, and the organs are usually very imperfect. Transformation in the other direction, that is, from specialized to less spe cialized organs, is so common that they are scarcely thought of as malformations. Thus pistils and stamens may develop as petals. a transformation which occurs in most double flowers; petals may he transformed into sepals, or even into imperfect foliage leaves. Indeed, all parts of the flower may he developed as irregular green leaves, of which the so-called 'green roses' gans, occurs most commonly in the floral regions. Some double flowers owe their origin purely to t i s phenomenon.
The increase may affect the number of parts in a whorl, or t he number of whorls. In the Ba hia or navel orange an additional num ber of carpels is reg ularly produced, and an imperfect. fruit develops. inclosed by the larger one. The so-called 'two-story apples' have their origin in a. similar change. Occasionally the additional car pels are lateral to the others, in which case an imperfect fruit, may be devel oped alongside the 11101T perfect one.
Al al format ions d f fer strikingly from galls in the process of their formation, which is due to in trinsic causes,where as galls result from some extrinsic cause such as the presence in the plant tissues of inseets. mites, worms, fungi, slime molds, etc., or from the secretious of these crea tures, or from the presence of both organisms and secretions. Like malformations, galls may appear upon the roots, stems, leaves, or flowers, and may present very diverse abnormalities. par ticularly as to their external form and to the peculiar and special tissues which compose them.
BIBLIOGRAPHY. The most important works are Bibliography. The most important works are the following: Moquin Tandon, Elements de tera tologie regrtale (Paris, 1841) ; Masters, Vege table Teratology (London. 1869) ; Penzig, zenteratoloyie (Genoa, 1890-94). in which the ex tensive literature up to its date is cited. See GALLS.