Wattle trees can be grown on soil that is unsuitable for agriculture, and there is every prospect of the industry expanding in South Africa, where a factory has lately been established for the purpose of converting the bark into an extract, which, it is said, will contain between 50 and 60 per cent. of tannin. By far the greater proportion of wattle bark is still exported in the natural form, ground or chopped, and packed into bags weighing about 1 cwt. each. Before the European War nearly the whole of the bark was shipped to Hamburg, English tanners taking very little interest in it, although it was largely used by German tanners. But since the supplies of the materials favoured by British tanners have become somewhat restricted, attention has been drawn to the value of mimosa bark. DIVI-DIVI (_caesalpinia coriaria_) is the dried pods of a Central American tree. It has also been successfully cultivated in India. The pods are rich in tannin, containing anything from 40-50 per cent., but its value is discounted by its liability to fermentation, which, however, may be checked to some extent by the use of antiseptics, such as carbolic acid, formaldehyde, or by the addition of synthetic tannin, neradol. If this tendency to fermentation and oxidation of the colouring matter could be checked completely, divi-divi would be a valuable material, as it makes a firm leather of good colour. When dried, the pods curl up in the shape of the letters S and C. The tannin is found in the husks of the pod. The seeds, which contain no tannin, are so hard that it has not yet been found profitable to extract the oil from them. Very similar tanning materials to divi-divi are cascalote, indigenous to Mexico, and algarobilla (_caesalpinia brevifolia_) which grows in Chili. Cascalote is chiefly used by Mexican tanners and is rarely exported. Algarobilla is not available in large quantities, otherwise it would be largely used in Great Britain, as it does not ferment so readily as divi-divi, and is even richer in tannin.