CROP-PLANTS 359 



from Amani. A new testing machine was designed and made at 

 Amani in 1933, and as a result standard methods for sampling 

 have been adopted. Another centre of sisal research is at Ngomeni 

 in Tanga Province, where field trials and investigations of the sisal 

 weevil have been in progress. Blue sisal, A. amaniensis, has been 

 developed from a plant of unknown origin discovered near Amani 

 in 1933 (Nowell 1933). This has been propagated, and in 1936 

 was established on a field scale at Mlingano (Stockdale 1937). 



Researches which promise to be of much value in effecting a per- 

 manent improvement in the condition of the sisal industry in East 

 Africa have been stimulated by the Imperial Institute. The inclu- 

 sion of experts from the Admiralty on the Imperial Institute 

 Committee on Vegetable Fibres has had important and valuable 

 results, and a series of trials were made on sisal ropes side by side 

 with hemp and other standard ropes. The results, published in 

 the bulletin of the Imperial Institute (193 1-3), have proved very 

 satisfactory, and for many purposes sisal ropes are now issued to 

 the Fleet. The Empire Marketing Board in the last year of its 

 existence also paid much attention to sisal, and the resulting publi- 

 cations have improved methods of cultivation and the industry as 

 a whole (Barker 1933). Research on the utilization of sisal and its 

 by-products is carried out on behalf of producers in Tanganyika 

 and Kenya by the Linen Industry research station at Lambeg in 

 Ireland in co-operation with the East African sisal research 

 organization. 



ROOT CROPS 



The root crops indigenous to Africa are Dioscorea rotundata, the 

 common or white yam of West Africa, of which many varieties are 

 grown; D. cayennensis, the yellow, negro or Guinea yam, a West 

 African species of which also many varieties are grown, though 

 it is less popular than the common yam; D. hispida var dumetorum, 

 the Esuri yam of West Africa; D. bulbifera, the Akom or Air potato 

 also found in Asia; Coleus dysentericus, the Hausa or Madagascar 

 potato, which is grown throughout Africa and Madagascar 

 wherever conditions are suitable, and extends as far south as 

 Mashonaland; Plectranthus floribundus, the Kafir potato; and Spheno- 

 stylis stenocarpa^ which is cultivated in Nigeria as a root crop. Early 



