Galls or plant galls are abnormal outgrowths of plant tissues and can be caused by various parasites, from fungi and bacteria, to insects and mites. Galls are often very organised structures and because of this, the cause of the gall can often be determined without the actual agent being identified. This applies particularly to some insect and mite galls.
Causes of plant galls
InsectsInsect galls develop under the influence of gall-inducing insects. Insect galls are usually induced by the chemicals injected by the larvae or the adults in the plants, either including mechanical damage or not. After the galls are formed, the larvae develop inside until fully grown, at which time they leave, sometimes as adults. In order to form galls, the insects must seize the time when plant cell division occurs at a high speed, the growing season, usually spring in temperate climates, but which can be extended in tropical latitudes. Also, the specific places where plant cell division occurs are needed to induce galls, that is, the meristems. Although insect galls can be found on a variety of parts of the plant, such as the leaves, stalks, branches, buds, roots or even flowers and fruits, gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they gall. Some insects induce galls on plants similar to each other, frequently within genera or family.
FungiA gall-inducing fungus is: Cedar-apple rust
Bacteria and virusesCrown Gall is an example of a gall-causing bacterium.
Other PlantsMistletoe can form galls on its hosts
Galls are rich in resins and tannic acid and have been used in the manufacture of permanent inks (such as iron gall ink) and astringent ointments, in dyeing, and in tanning. A high-quality ink has long been made from the Aleppo gall, found on oaks in the Middle East; it is one of a number of galls resembling nuts and called "gallnuts" or "nutgalls'. The larvae in galls is useful for a survival food and fishing bait.
image:Eikengallen op mannelijke bloeiwijze.jpg|Neuroterus albipes forma laeviusculus
nutgall in Catalan: Agalla (botànica)
nutgall in Danish: Galle
nutgall in German: Gallapfel
nutgall in Spanish: Agalla
nutgall in Esperanto: Gajlo
nutgall in French: Galle (botanique)
nutgall in Galician: Bugallo
nutgall in Italian: Galla (botanica)
nutgall in Hebrew: עפץ
nutgall in Lithuanian: Galas
nutgall in Dutch: Galappel
nutgall in Japanese: 虫こぶ
nutgall in Polish: Galasy
nutgall in Portuguese: Galha
nutgall in Chinese: 癭