GALLS 413 



young shoots of the oak. The larva emerges from the egg and wounds 

 the delicate tissue with its mandibles, simultaneously introducing 

 into the tissue a secretion that stimulates a rapid development of 

 tissue. The new tissue thus formed assumes an concentric arrangement 

 and within this the larva lives, feeding upon starch produced by the 

 cells. Arrived at maturity the larva passes into the pupa stage, from 

 which the wasp emerges and, boring through the gall with its 

 mandibles, escapes. The gall is therefore probably to be regarded as 

 a metamorphosed shoot. Very remarkable is the fact that no 

 development of tissue takes place until a glandular secretion passes 

 from the mandibles of the larva into the surrounding tissue, which 

 is always merismatic in nature ; this formation of tissue continues as 

 long as the exciting substance is supplied, but should the larva perish 

 it at once ceases and the growth of the gall is arrested. 



Galls should be collected preferably before the insect escapes ; 

 after that has happened they 

 become lighter in weight and 

 are less esteemed. 



Description. Aleppo galls are 

 nearly spherical in shape and 

 vary from 12 to 20 mm. in 

 diameter. They are hard and 

 heavy,, and bear, especially in FIG. 232. Galls. A, showing interior ; 

 the upper portion, short, bluntly B > exterior, both with hole bored by 



pointed projections. They are 

 of a bluish green or olive green 



colour externally, yellowish or brownish white within. There is 

 usually a small cavity in the centre, in which the remains of the 

 larva or of the gall-wasp may be found. They have no odour, but 

 an intensely astringent taste followed by a slight sweetness. 



Constituents. Galls contain as principal constituent from 50 to 

 70 per cent, of tannic acid, which, to distinguish it from other varieties 

 of tannic acid, is termed gallotannic acid. They contain also a little 

 gallic acid (2 to 4 per cent.), ellagic acid, cyclogallipharic acid, sugar 

 and starch. 



Gallotannic acid, the ' tannic acid ' of the British Pharmacopoeia, 

 is a pale yellow amorphous substance yielding bluish black precipi- 

 tates with solutions of ferric salts. Its aqueous solution darkens 

 when exposed to the air with simultaneous formation of gallic acid, 

 C 7 H 6 O 5 ,H 2 O, and sometimes also of ellagic acid, C 14 H 6 O 8 ,2H 2 O. 



. Galls are used medicinally as a local astringent chiefly in 

 the form of a suppository or ointment. They find an extensive 

 application technically in tanning and dyeing, in the manufacture of 

 ink, &c. 



