256 



TROPICAL AGRICULTURE 



CHAP. 



The sowing West Indies for sowing indigo, the cutting operations will 

 commence in June. The plants are usually cut down to 



season. 

 Cutting. 



Rattooni 



Blights. 



Manures. 



up in bundles to be carried to the place where the indigo is 

 manufactured. As exposure to the sun injures the cut plants, 

 the operation should be begun and finished in the afternoon. 

 After being cut down the plants will rattoon ; and, in favour- 

 able circumstances, as many as four cuttings have been 

 obtained from the same roots in a year ; but this is unusual 

 for the plants quickly deteriorate, and seed must be freshly 

 sown every year. 



The indigo plant is liable to be attacked by many insect 

 enemies, which in. some instances so infest the leaves as to 

 destroy the entire crop. Some species of caterpillars are ex- 

 tremely fond of the leaves, and when the plant is cultivated 

 on the same soil in succeeding years the enemies increase 

 greatly in numbers ; it has been advised, therefore, that fresh 

 soil should be chosen every year. 



Indigo contains a considerable proportion of nitrogen, and 

 thus when the same land is cropped often, manures rich in 

 ammonia should be used. The refuse of the plants, after the 

 indigo is extracted, is perhaps the best manure, and it makes 

 an excellent fuel. Where the refuse cannot be returned to 

 the soil, farm-yard manure with a top dressing of lime will 

 answer the purpose very well. 



Manufacture of the DvE.—The substances which form 

 indigo reside in the leaves, but the whole plant for the sake 

 of convenience and economy is subjected to the process of 

 fermentation and agitation by which the dye is manufactured. 

 How the dye The fermentation of the plants under water causes the dye 

 matters to be dissolved out ; and these, combining with the 

 oxygen of the air, produce the blue colouring substance known 

 as indigo. On a small scale indigo may be made experi- 

 mentally by infusing the leaves in hot water, when the dye 

 will be deposited by allowing the infusion to stand exposed 



is formed. 



The dye 

 made expe 

 rimentally. 



