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active tissue that constitutes the “‘sap-wood.” From such 
trunks the sap-wood is therefore usually trimmed off before 
the logs are sent to market. In most cases, dye-stuffs 
show some coloration to indicate the presence of their 
coloring matters, although the color thus seen may be 
quite a different one from that which the material will 
produce when in practical use. Sometimes no coloration 
is to be seen in the dye-stuff, some chemical treatment 
being necessary to develop it. 
Although the use of anilin or coal-tar colors has very 
largely replaced that of vegetable dyes, there is still a vast 
use of the latter. But for the introduction of the former, 
it is dificult to see how the demand for colors could have 
been supplied under modern conditions. 
Tanning Materials. Cases 37 to 38.—The tanning 
materials are also very important from an economic stand- 
point. They depend for their value chiefly upon the 
tannic acid that they contain, but that other constituents 
contribute is clear from the fact that a substance containing 
less tannin may be more valuable than one containing a 
larger percentage. The tannin cures and toughens the 
skin, but other effects are required to produce the best 
quality of leather, especially that of “‘filling” the minute 
cavities. For this purpose white-oak bark seems to be 
preéminent and this continues to be the most valued tanning 
substance. It has become scarce and costly, and “oak 
leather’’now brings the highest prices. The tannins are 
represented by saw-palmetto, mangrove, pine, hemlock, 
and sumac. The crude materials of the mangrove and 
the saw-palmetto are accompanied by their fluid extracts, 
which contain the tannic acid, and also by the spent 
material or refuse which remains after the extract has been 
made. This latter material may be used for other purposes. 
Fodder Plants. Cases 39 and 40.—Following the spices 
are fodder plants, which are shown as sheaves. Fodders 
are derived chiefly from plants of the grass and bean fami- 
lies. Illustrations of the former are the varieties of hay 
