(or cedicia), local pathological neoplasms on the organs of plants caused by special species of irritants and providing these irritants with a dwelling place and a source of food. Galls caused by invertebrate animals are sometimes called zoocecidia; those caused by fungi are called mycocecidia. The formation of galls is called gallogenesis and the irritants are called gallogens. The latter include viruses, bacteria (for example, Agrobacterium tumefaciens, which causes crown galls and goiters on the roots of apple trees), fungi (such as the irritant that causes bubble smut in corn), nematodes (especially rootknot nematodes), mites (quadrupeds), and insects (mainly gall wasps, gall midges, sawflies, aphids, and jumping plant lice); all of these lead a parasitic existence. Gallogenesis takes place in several steps and is stimulated by secretions from the salivary glands of the female irritants while they are laying the eggs, from the salivary glands of the larvae, and from the growing tubes of germinating spores, which contain certain free amino acids, compounds of an indol nature, and so forth. The further progress of gallogenesis is associated with local changes in the synthesis and metabolism of certain amino acids, phenol compounds, and proteins. The origin of crown galls, used as models in the study of tumor growth in animals and man, is linked to changes in the DNA in the infected cells of the organism. The structure of a gall depends on the type of the irritant, the nature of its localization in the infected organ, the number of individual irritants in the developing gall, the degree of mobility of the irritant, and the morphological structure of the infected tissues. The pathogens of many galls cause considerable damage to agriculture and forestry. They include the pathogens of potato canker, cabbage carina, bubble smut in corn, warts in geraniums, silver fir tree canker, and phylloxera in grapes. The pathogens of certain galls are used in the biologist’s fight against weeds. The galls on oaks, sumac, and pistachio trees contain a considerable amount of tannin.