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_ The experiments of M. Vaucquelin shew, that of 
one hundred parts of buckwheat, fifty are carbonate 
aad sulphate of potash and carbonate of lime. 
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SECTION X. 
of other plants useful in avotation of crops, 
and adapted to our climate. 
These may be brought under three classes ; those 
which yield a coloring matter, those which yield oil, 
and those whose bark is convertible into clothing. 
Of the first, are madder, saffron and woad; of the 
second, poppy, colzat and palma christi; and of the 
third, flax and hemp. 
I. Of Madder. 
Madder isthe Erythros of the Greeks, and the Ru- 
bia of the Latins; so called from its imparting a red 
color to wool and leather. It is cultivated in the 
Levant, in France, in Flanders, and in England ; 
but no where more extensively or profitably than in 
Holland. The province of Zealand is principally 
occupied with it, and the little island of Schowen 
alone gives annually one thousand tons of the root. 
The species generally cultivated are two—the 
Azara and Izari; names by which they are called 
in the Levant, whence the seed is generally import- 
ed to Europe, and preferred to that raised in more 
northern latitudes. 
The soil most proper for this plant is rich loam, 
and the manures-fittest for it the sweepings of streets 
