A. penninervis (Hickory bark) is said to be particularly hardy, but its strength seems to vary. A sample from Bateman’s Bay contained 38 per cent. of tanning matter.
A. binervata, another “Black Wattle” contains up to 30 per cent. tanning matter, as does also the “Weeping Willow,” A. saligna. The latter is poisonous, and is said to be used for killing fish.
A. prominens, the bark of which resembles that of the Golden Wattle, A. longifolia, in appearance contains only 14 per cent. tannin.
The cultivation of wattles in Australia has been somewhat neglected, but would render possible the utilisation of many acres of land lying waste, or which have already been exhausted and rendered unfit for the growth of cereals. It requires so little attention as to make it very profitable, and wattle-growing and sheep-grazing can be combined satisfactorily after the first year, when the young trees in the plantation have reached the height of 3-4 feet. In Natal the Australian wattles, especially A. mollissima, have been acclimatised and cultivated with success, and large quantities of excellent bark are now exported to England. African wattle-barks usually contain about 30 per cent. of tannin.
Wattles grow in almost any soil, even the poorest, but their growth is most rapid on loose, sandy patches, or where the surface has been broken for agricultural purposes. When the soil is hard and firm, plough-furrows should be made at a regular distance of 6-8 feet apart, and the seeds dropped into these. The seed should be sown in May, having been previously soaked in hot water, a little below boiling temperature, in which they may be allowed to remain for a few hours. It should be dropped at an average distance of 1 foot apart along the furrow, in which case, about 7200 seeds would suffice for one acre of land. The seed should not be covered with more than about 1⁄4 inch of soil.
On loose sandy soil, it might even be unnecessary to break up the ground in any way; the furrows may be dispensed with, and the seed sown broadcast after the land has been harrowed. After the plants have come up, they should be thinned so that they stand 6-8 feet apart. When the young trees have attained the height of 3-4 feet, the lower branches should be pruned off, and every effort afterwards made to keep the stem straight and clear, in order to facilitate the stripping, and induce an increased yield of bark. It is advisable that the black and broad-leaved kinds should be grown separately, as the black wattle, being of much larger and quicker growth, would oppress the slower-growing broad-leaved one. Care should be taken to replace every tree stripped by re-sowing, in order that there should be as little variation in the yield as possible. In Victoria, the months of September-December are those in which the sap rises without intermission, and the bark is charged with tannin. Analysis proves that the bark from trees growing on limestone is greatly inferior in tannin to that obtained from other formations, differing 10-25 per cent.
The following are South American mimosas:—
A. cavenia, Espinillo. Bark, contains 6 per cent., pods, 18-21 per cent., or more of tannin.
A. cebil, Red Cebil. Bark, contains 10-15 per cent.; leaves, 6-7 per cent. tannin. Argentine Republic.
A. Guarensis, Algarobilla of Argentine Republic. Bark, pods and flowers said to be used for tanning.