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English: Trihydroxybenzoic Acid
Minerals; Organic Compounds; Acyclic Carbon Compounds; Cyclic Carbon Compounds
Proved and introduced by D.S. Kimball; Allen: Encyolop. Mat. Med., Vol. IV, 37; Clarke: A Dictionary of Practical Mat. Med., Vol. I, 795.
Description of the substance
Galls are excrescences produced in plants by the presence of the larvae of different insects. The forms that they assume are many, and the changes produced in the tissues various. They occur in all parts of the plant and sometimes in great quantities.
The oak galls used in commerce and medicine are excrescences on the Q. infectoria, a small oak, indigenous to Asia Minor and Persia, and result from the puncture of the bark of the young twigs by the female Gallwasp, Cynips Gallae-tinctoriae, who lays its eggs inside. This species of oak seldom attains the height of 6 feet, the stem being crooked, with the habit of a shrub rather than a tree.
The Common Oaks of this country are much affected by galls. They occur sometimes on the leaves, where they form the socalled 'Oak-apples,' sometimes on the shoots, where they do great mischief by checking and distorting the growth of the tree.
The young larva that hatches from the eggs feeds upon the tissues of the plant and secretes in its mouth a peculiar fluid, which stimulates the cells of the tissues to a rapid division and abnormal development, resulting in the formation of a gall.
The larva thus becomes completely enclosed in a nearly spherical mass, which projects from the twig, furnishing it with a supply of starch and other nutritive material.
The growth of the gall continues only so long as the egg or larva lives or reaches maturity and passes into a chrysalis, from which the fully-developed gall-wasp emerges and escapes into the air through a hole bored with its mandibles in the side of the gall.
The best Aleppo galls, collected in Asiatic Turkey, principally in the province of Aleppo, are collected before the insects escape.
Galls are also largely imported from Persia and to a lesser extent from Greece.
Aleppo Galls of good quality are hard and heavy, without perforations, dark bluish-green or olive green, nearly spherical in shape, 12 to 18 mm. in diameter (about 2/5 to 4/5 inch), and known in commerce as blue or green galls.
The Aleppo galls (from Q. infectoria) sometimes also called 'Mecca Galls,' are supposed to be the Dead Sea or Sodom Apples, 'the fruit that never comes to ripeness' - the fruit so pleasant to the eye, so bitter to the taste.
If collected after the insects have escaped, galls are of a pale, yellowish-brown hue, spongy and lighter in weight, perforated near the centre with a small hole. These are known in commerce as white galls.
On breaking a gall, it appears yellowish or brownish-white within, with a small cavity containing the remains of a larva of the Gall-wasp.
Galls have no marked odour, but an intensely astringent taste, and slightly sweet after-taste.
Source, History, and Formation.—Though existing in a number of astringent plants, the greater portion of commercial gallic acid is derived from nutgalls (more). Scheele (1785), who first obtained it pure, established its non-identity with tannic acid. The manner of formation of gallic acid from nutgalls has been a subject of much discussion and experimentation. Before investigations were begun it was believed to exist ready-formed in galls, but in 1833 Pelouze showed that the larger portion of it was derived from the tannin of the galls, and advanced the theory that this conversion was accomplished by oxidization by the atmospheric oxygen, by which carbon dioxide was driven off. The elder Robiquet (1837) showed that its conversion could be accomplished without the aid of oxygen and without evolving carbon dioxide, but that it resulted from a ferment called pectase. Wetherill (1847), and subsequently, Mulder (1848), attempted to show that tannic acid differed from gallic acid only in the possession of a larger amount of water of crystallization. Liebig believed the change to be due to the liberation of a carbohydrate. In 1854 Strecker came to the conclusion that tannin was a glucosid, for by boiling it with diluted mineral acid he obtained a large amount of gallic acid and considerable glucose. This view was generally accepted for a long time, though opposed by the younger Robiquet (1854) and Hlasiwetz (1867), who advanced different theories regarding the supposed glucosid. The present theory is that advanced by Schiff (1871) and supported by others, that pure tannic acid be viewed as digallic acid (this being the first anhydrid of gallic acid), and that natural tannin is the glucosid of pure tannic, or digallic acid, for by the action of hot diluted mineral acids or a nitrogenous ferment upon it, digallic acid and glucose are evolved.
Phytochemistry. 2004 Oct;65(20):2809-13. Related Articles, Links
Biosynthesis of gallic acid in Rhus typhina: discrimination between alternative pathways from natural oxygen isotope abundance.
Werner RA, Rossmann A, Schwarz C, Bacher A, Schmidt HL, Eisenreich W.
Institut fur Pflanzenwissenschaften, ETH Zurich, LFW C48.1, Universitatsstr. 2, CH-8092 Zurich, Switzerland.
The biosynthetic pathway of gallic acid in leaves of Rhus typhina is studied by oxygen isotope ratio mass spectrometry at natural oxygen isotope abundance. The observed delta18O-values of gallic acid indicate an 18O-enrichment of the phenolic oxygen atoms of more than 30 per thousand above that of the leaf water. This enrichment implies biogenetical equivalence with oxygen atoms of carbohydrates but not with oxygen atoms introduced by monooxygenase activation of molecular oxygen. It can be concluded that all phenolic oxygen atoms of gallic acid are retained from the carbohydrate-derived precursor 5-dehydroshikimate. This supports that gallic acid is synthesized entirely or predominantly by dehydrogenation of 5-dehydroshikimate.
COMMON OAK GALLS
by Lee Townsend, Extension Entomologist, and Eileen Eliason
University of Kentucky Department of Entomology
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.
Gall makers must attack at a particular time in the year to be successful. Otherwise, they may not be able to stimulate the plant to produce the tissue which forms the gall. Generally, initiation of leaf galls occurs around "bud break" or as new leaves begin to unfold in the spring.
Twig and Stem Galls
Twig and stem galls, such as the gouty oak gall and horned oak gall, are solid, woody masses that can girdle branches or make them droop from the sheer weight of the heavy growths. The galls can grow to more than 2 inches in diameter. Horned oak galls can be found on pin, scrub, black, blackjack, and water oaks while gouty oak galls occur on scarlet, red, pin or black oak.
These galls have a long and complex development that takes two or more years to develop. The first stage is a blister-like leaf gall that occurs along larger leaf veins. The second stage is a knotty twig gall that is started in mid-summer and becomes fully mature in 1 to 2 years. Adults emerge in the spring. Gouty oak twig galls are smooth; hormed oak galls have horn-like projections. One female wasp can emerge from each horn.
Generally, insecticidal control is not satisfactory because the wasps are physically protected within the galls. Correctly timing applications to provide effective preventive control is difficult. Where practical, pruning of infested twigs may help to reduce the problem on lightly-infested trees. However, pruning is impractical if large trees are heavily infested. A commercial arborist may be able to provide assistance with valuable plantings.