Galls
Gall Gall, also cecidium, swelling or excrescence of plant tissues caused by the action of parasites. Such swellings, which may occur on any part of a plant but are usually found in regions of active cell division and growth, are initiated by the chemical action of secretions of infesting organisms, usually insects or fungi. Galls assume a great variety of forms; each form is characteristic of the parasite that causes it, and usually each species of gall-forming parasite infects a specific organ of a specific plant. The growth of the gall may result either from a tremendous swelling of the individual cells or from the rapid division of cells near the point of attack by the parasite. The gall provides a protective capsule for the parasite while it feeds on the plant. The most striking galls are caused by insects that begin their invasion by laying eggs in plant tissues. The resultant enlargement of surrounding tissue is caused either by growth-promoting stimulation furnished by the eggs