CROP-PLANTS 375 



petit-grain oil have been marketed and it is hoped to produce 

 lemongrass oil on a commercial basis in the Eastern Province. 

 There has already been a small export of the latter oil. Results of 

 research at Amani are outlined in a paper by the biochemist, Dr. 

 R. R. Worsley (1934a). Experimental production of certain oils 

 has also been carried out in Uganda and Nyasaland. In Rhodesia 

 the production of citrus and other oils is being undertaken. Essen- 

 tial oils have the advantage of economic transport, since the oil is 

 prepared on the farm, but production can only be profitable where 

 labour, fuel and water are abundant. Considerable capital is 

 required for the equipment necessary to deal with the raw material. 



During the last five years a thriving industry has been built up 

 in the Kenya highlands, in the production of dried Pyrethrum 

 flowers for which there is a good demand in the manufacture of 

 insecticides. The main producing areas lie between 7,000 and 

 9,500 feet and in general there is a progressive increase in yield 

 with altitude between these limits. The average yield of dried 

 flowers per acre is from 1,000 to 1,500 lb. The yields at lower 

 altitudes are not considered economic under normal market con- 

 ditions, but with the present high prices, cultivation is carried out 

 at 5,000 feet upwards. Pyrethrum requires a fairly low average 

 temperature and also at least one dry season a year in order to 

 rest the plants. For these reasons trials at low altitudes in the 

 tropics have so far proved unsuccessful. 



Pyrethrum is grown in Tanganyika, under conditions similar to 

 those in Kenya. The yield is approximately the same and a small 

 export trade has now been started. 



Derris is another insecticide crop which shows promise, particu- 

 larly in East Africa. It thrives under humid tropical conditions and 

 high quality material has been grown on a fairly large experimen- 

 tal scale at Amani in Tanganyika. Successful experimental work 

 with derris has also been carried out in Nyasaland and Uganda. 



Several other plants, used by the natives as fish poisons and 

 similar in toxic properties to derris, are fairly widely distributed 

 throughout the African continent. Among these may be mentioned 

 Mundulea suberosa, Tephrosia vogeli, and species of Lonchocarpus, 

 all of which have been investigated, but hitherto have not been 

 found to compare favourably with high-quality derris. 



