232 POPULAR ECONOMIC BOTANY. 



bescent or hairy below ; the young stems have the same pe- 

 culiar indigo-green tint. The flowers are pea-shaped, borne 

 in short racemes, springing from the axils of the leaves; 

 they are a pale rose or red colour. Besides Indigofera tine- 

 toria, I. Anil and I. c&rulea are much used in the manu- 

 facture of indigo; according to Roxburgh, that from the 

 last-mentioned plant is the best. Owing to the insolubility 

 of indigo in water, the art of dyeing with it consists in a 

 very complicated process, so purely technical that it would 

 be out of place in a popular work like the present. The 

 fine Saxon blue cloths are dyed with this material. 



The principal varieties recognized in commerce are — 

 Bengal ; Oude ; Manilla ; Madras ; Caraccas ; Spanish 

 Floras; Spanish Sobres; and Spanish Cortes. The aver- 

 age price is about three shillings per pound. The enormous 

 quantity of 3524 tons of this vegetable extract was imported 

 in 1851, but of this quantity more than one-half was sold 

 to foreign merchants and re-exported to other countries. 



The colouring matter of Woad {Isatis tinctoria), used by 

 the ancient Britons, was analogous to indigo. 



Lac Dye in many respects resembles indigo, but, being 

 partly an animal product (a secretion of the Lac insect, 

 Coccus laced), further notice of it would be out of place 

 in this work. 



