440 THE MADDER CROP. 



Rhizoctonia (a genus of parasitic plants very imperfectly 

 known at present) on the roots of the madder, which speed- 

 ily covers them with a thick filamentous network and 

 destroys them. 1 



The value of madder consists in the colouring matters 

 contained in the roots. If a transverse section be made, 

 a difference is readily seen not only in the structural for- 

 mation, but also in the colour of the different parts the 

 centre being the darkest, and the colour declining gradu- 

 ally in hue to the outside layers, where the red has changed 

 into an orange yellow colour. In some cases the roots 

 are divided, and the different portions treated separately, 

 the finer qualities being obtained from the heart or inner 

 parts of the root. In like manner roots of old plants con- 

 tain more of the valuable colouring principle than those 

 of younger plants; in the countries of the East, where 

 the dye is prepared, this fact is well known. The two 

 principal dyes obtained from madder are red and yellow 

 in colour; the one, whose discovery was due to a French 

 chemist, Robiquet, is known by the name of "Alizarine," 

 the other by the name of "Xanthine." The roots of Euro- 

 pean growth contain more of the yellow and less of the 

 more valued red dye than those grown in the Levant and 

 other countries of the East, and as a consequence fetch a 

 lower price in the market. 



The fresh roots contain about 80 to 85 per cent, of 

 water; 12 to 18 of extractive matter, and about 1-5 to 

 2 '5 per cent, of salts or inorganic matter. 



The composition of the dried root is thus given by John 



Fatty matters, TO 



Red resin, 3'0 



Colouring matters, 20 '0 



Extractive matters, 5'0 



Gum and cellular fibre,.. 43' 5 



1 De Gasparin, Mcmoircs <TAyri. tome ii. p. 284. 



