Nutgalls

NUTGALLS

Synonyms

Nutgalls, blue galls, Turkish galls.

Biological Source

Nutgall consists of the pathological outgrowth obtained from the young twigs of the dyers oak, Quercus infectoria Olivier, belonging to family Fagaceae. Outgrowth is caused by the puncture of ovums of insect Cynips tinctoria or Adleria gallaetinctoriae Olivier Family Cynipidae.

Geographical Source

Oak galls are obtained principally from Asiatic Turkey. Dyers oak is found in Turkey, Syria, Iran, Cyprus, and Greece.

Collection and Preparation

Larvae of the insect C. tinctoria after emerging from the eggs, pierces the delicate epidermis near the growing point of the twigs where the eggs are deposited by the insect. The gall begins to enlarge, when the chrysalis stage is reached, starch disappears from the neighbourhood of insect and is replaced by gallic acid, whereas central cells consist of tannic acid. The insect passes through the larval and pupal stages. If the galls are not collected and dried at this stage the mature insect comes out of the gall and escapes, and during this stage galls changes the colour from a bluish grey, through olive-green to almost white. After the escape of the insect, a central cavity is formed, and the tannic acid is oxidized in the presence of moisture and air. The more porous gall is the white gall of commerce.

In Asiatic Turkey, galls are collected before the escape of the insect in the months of August and September. After drying, they are sorted out according to colour into three grades, that is, blue, green, and white and exported.

Microscopy

A transverse section through a nutgall show thin walled parenchymatous outer zone, which is quite larger as compared to inner zone. Parenchyma is followed by a ring of sclerenchyma composed of one or two layers of suberised cells. Inner zone is made up of thick walled parenchyma, which surrounds central cavity. Cells of parenchyma show the presence of numerous starch grains, calcium oxalate clusters and rosettes and tannins. Parenchyma also shows the bodies of lignified tissues, which stains with phloroglucinol and hydrochloric acid.

Chemical Constituents

Nutgalls contains about 50–70% tannin mainly gallotannic acid which is official tannic acid. It also consists of 2–4% gallic acid, ellagic acid, sitosterol, methyl belulate and methyl oleanolate which are methyl esters of betulic and oleanolic acid. Recently few more compounds such as Nyctanthic acid, roburic acid, and syringic acids have been reported from galls. It contains abundant starch.

Tannic acid of commerce is a hydrolysable tannin which yields gallic acid and glucose. The molecule of tannic acid may contain the gallic acid up to pentagalloyl glucose. It is isolated by fermentation and subsequent extraction of galls with water-saturated ether.

Uses

Nutgall is the major source of tannic acid, which is largely used in tanning and dyeing industry and for the manufac-ture of ink. It is used medicinally as a local astringent in ointments and suppositories.

Allied Drugs

Various types of galls are produced on plants by insects of the genera Cynips and Aphis. Chinese and Japanese galls are of commercial interest. These galls are formed on Rhus chinensis Mill, family Anacardiaceae by an aphis, Schlectendalia chinensis. These galls are knoty, grey, irregular and breaks easily to show irregular cavities. They contain 57–77% of tannins. These drugs have been used in China and Japan since time immemorial as astringent and styptic.