The tannin contained
in the sap does not increase in the same ratio as does the rapid
growth, and it follows that the remainder in the bark is less than in
the tree of slower growth.
_Birch Bark_--Is at home in Russia, Norway, and Sweden. It is used for
both upper and sole leather, but seldom alone. The bark is usually
peeled from the full grown tree, and contains 4 to 9 per cent. tannin.
_Willow Bark_--May also be found in the above mentioned countries and
also in Germany. This material is used for both upper and sole
leather, and contains 6 to 9 per cent. tannin. It is a very delicate
material to use, as its tannin decomposes rapidly.
_Erlen Rinde_--Is also a native of Germany, but is not used to any
great extent. The same may be said of the larch, although this variety
is also to be met with in Russia.
_Mimosa Bark_--Is obtained from the acacia of Australia. It is a
favorite in England. The varieties are as follows: Gold wattle, silver
wattle (blackwood, lightwood), black wattle, green wattle. The gold
wattle is a native of Victoria. Its cultivation was tried as an
experiment in Algeria and met with some success. The trees are always
grown from seeds. These seeds are laid in warm water for a few hours
before sowing. The acacia may be peeled at eight years' growth and
carries seeds. The Tasmania bark is very good; that from Adelaide
likewise good.
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