118 AGRICULTURE IN THE TROPICS [PT. II 



Gingelly oil, the oil of Sesamum indicum, is another oil of 

 considerable importance, though it is but little exported. No 

 less than 2,500,000 acres in India and Ceylon are devoted to 

 this crop, which is a small herbaceous plant. The oil ex- 

 pressed from the seeds is used for culinary, soap-making and 

 perfumery purposes. 



Innumerable plants are used as sources of oil by the natives 

 of tropical countries, but the fact need only be mentioned 

 here. Other important sources of oil than those mentioned are 

 cotton-seed, in which oil there is a large and growing trade, 

 especially in the United States, niger-seed (Guizotia oleifera), 

 now largely grown in India, Africa, etc., castor-oil (Ricinus 

 communis), mustard (Brassica oleracea). 



Volatile Oils. Perhaps the most important of these is 

 citronella, in which a large trade has been carried on from 

 Ceylon for many years. The extreme south of the island 

 contains about 20,000 acres devoted to the cultivation of 

 citronella grass (Cymbopogon Nardus), and the export figures 

 in recent years have been over 1,000,000 Ibs. of oil per annum. 

 Of late, Ceylon oil having acquired a bad reputation from the 

 adulteration practised by the Sinhalese in whose hands the 

 cultivation is, Java has begun to take up the cultivation, with 

 properly equipped factories under European management, and 

 is turning out a much better quality of oil which commands 

 a much higher price. 



The grass is grown in tussocks on open hill slopes, is 

 cut every three months or so, and distilled by passing steam 

 through it, when the oil passes over with the steam and may 

 be condensed. An acre yields perhaps 30-50 Ibs. of oil in a 

 year, and the best varieties of the grass want replanting 

 every second or third year. The oil is mainly used in the 

 preparation of scented soaps, and is also a good preventive of 

 mosquito bites. 



Lemon-grass oil, the product of the grass Cymbopogon 

 citratus St., is as yet mainly grown in South India, but the 

 cultivation is also being taken up in Ceylon. The treatment 

 is the same as for citronella, but the grass is smaller, and 



