Distortions or Malformations may be defined as abnormalities in the form of organs which concern all, or nearly all the parts, and do not refer merely to swellings or excrescences on them or excavations, etc., in them.
Fasciation. - Shoots of Asparagus, Pine, Ash, and many other plants are occasionally expanded into broad ribbon-like structures often studded with more than the normal number of buds or leaves, etc., such as would be found on the usual cylindrical shoots. Such fasciations are due to several buds fusing laterally under compression when young and the whole mass growing up in common, or, in a few cases, to the unilateral overgrowth of one side of the terminal bud. Fasciations appear to depend on excessive nutrition in rich soils. They may spread out above in a fan-like manner, exaggerating the abnormality, or they may revert to the original form. Some cases are more or less fixed by heredity - e.g. Celosia. Fasciated stems are frequently curved like a crozier, owing to one edge growing more rapidly than the other.
Cauliflowers are really cultivated monstrosities.
Fasciated Dandelions, Crepis, monstrous Chrysanthemums, peloric Linaria, five-leaved Clovers, spiral Teazels, etc., may all, if grown with care, be kept more or less constant in the monstrous state. That is to say, the particular kinds of variation here manifested can be maintained in proportion as the external conditions controlling the variation are maintained. Such conditions are chiefly rich supplies of food-stuffs, plenty of water and air, suitable temperature and lighting, etc. Mutilations, favouring the development of abnormal buds may also induce fasciations.
Torsions or spiral twistings of stems also frequently arise among plants grown in rich soils, and are often combined with fasciations - e.g. Asparagus, Dipsacus; and De Vries has shown that the peculiarity is not only transmissible by seed, but may be more or less fixed by appropriate culture.
Contortions of stems are often due to the unequal growth on different sides of the stems owing to the presence of fungi - e.g. Caeoma on Pines, Aecidium on Nettles, also Puccinia on petioles of Mallow, Cystopus on inflorescences of Capsella, etc.
Distortions of roots may be brought about in various ways by the hindrances afforded by stones.
Spiral roots occur occasionally in pot plants.
Flattened roots usually result from compression between rocks, the young root having penetrated into a crevice, and been compelled to adapt itself later. The distortions of stems by constricting climbers, wire, etc., have been described, and fruits - e.g. Gourds - are easily distorted by means of string tied round them when young.
Distortions of leaves are very common, and are sometimes teratological - i.e. due to no known cause - e.g. the pitcher-like or hood-like cucullate leaves of the Lime, Cabbage, Pelargonium, etc., and of fused pairs in Crassula. Also coherent, bifurcate, crested, displaced and twisted leaves occasionally met with, and in some cases fixed by cultivation, may be placed in this category.
Puckers must be distinguished from pustules, since they consist in local upraisings of the whole tissue, not swellings - e.g. the yellowish green pockets on Walnut leaves, due to Phyllereum.
Puckered leaves in which the area of mesophyll between the venation is increased by rising up in an arched or dome-like manner are sometimes brought about by excessive moisture in a confined space.
Leaf-curl is a similar deformation caused by fungi, such as Exoascus on Peaches.
Wrinkling or puckering of leaves is also a common symptom of the work of Aphides - e.g. Hops.
Characteristic curling and puckering, with yellow and orange tints, of the terminal leaves of Apples, Pears, etc., are due to insects of the genera Aphis, Psylla, etc.
Small red and yellow spots with puckerings and curlings of the young leaves of Pears, the spots turning darker later on, are due to Phytoptus.