Galls are irregular plant growths which are stimulated by the reaction between plant hormones and powerful growth regulating chemicals produced by some insects or mites. Galls may occur on leaves, bark, flowers, buds, acorns, or roots. Leaf and twig galls are most noticeable. The inhabitant gains its nutrients from the inner gall tissue. Galls also provide some protection from natural enemies and insecticide sprays. Important details of the life cycles of many gall-makers are not known so specific recommendations to time control measures most effectively are not available.
A gall is a plant structure formed by abnormal growth within plant tissues
The growth is a reaction to a parasitic attack on/in the plant's cells
Galls are numerous, widespread, and come in a variety of shapes and colors
Excluding viruses, there are 5 major gall-causes: Bacteria, Fungi, Nematode, Acarina and Insecta
Each species of gall-cause attacks a specific plant structure, such as the leaves or the roots
Because the gall-causers do not destroy the plant, but slowly uses its' nutrients, they can be called parasites
The parasites can move inside or remain outside of the plant structures
In either case, the parasites act only as a growth stimulus
The gall is made up entirely of the plant's (the host's) tissues
The plant reacts to the parasite's intrusion by increasing the number of plant cells or enlarge the cell's size
Gall tissues form a "bubble" around the gall-causes in order to separate the parasites and any of their harmful by-products from the rest of the plant
Therefore, the gall is the plant's way of protecting itself from intruders
