CROP-PLANTS 373 



the wattle industry and cultivation has been so successful that the 

 value of the products in 1930 was ;;(^2,ooo,ooo, of which bark for 

 tanning represents 56 per cent, pit-props 33 per cent, and fire- 

 wood 1 1 per cent. Improvements have been made mainly through 

 silviculture, and the success of the wattle has served as a stimulus 

 to other silvicultural research in South Africa. In recent years 

 wattles have been established in Kenya, mainly as a native crop. 

 An important industry has already arisen, and in the central 

 provinces wattle bark has been the main exportable commodity 

 (Kenya, Agriculture, 1933, D.R.). In the densely populated 

 Kikuyu and Kamba reserves the tree has proved valuable for 

 firewood and building. 



Cloves form the main export of Zanzibar and Pemba Islands. 

 Scientific study on the plantations is an instance where co-opera- 

 tion between agriculturalists and forestry experts has proved 

 essential. A silviculturalist has been working recently in Zanzibar, 

 and results of much importance to the whole clove industry will 

 be published shortly. The Zanzibar experiment station had to 

 establish five new nurseries in 1936 in order to meet the demand 

 for selected seedlings from high-yielding parents. Regeneration 

 trials indicate that it may be advantageous after clear felling stands 

 of old cloves to put the land down to food and green manure crops 

 for a few years before replanting. It has been found that the seed- 

 lings benefit by shade during the first year of life in the field and 

 that interplanted cassava is the most suitable form of shade. Nutri- 

 tional trials indicate that phosphates and possibly potassium are 

 probably of greater importance than nitrogen to young cloves. 

 Trials have been made to determine whether the clove is self- or 

 cross-fertilized; and the means of control of the red ant and the 

 clove chafer have been investigated. (Zanzibar, Agriculture, 

 1936, D.R.; Stockdale 1937.) 



Tung oil is another tree crop only recently introduced to Africa. 

 The trees {Aleurites fordii and A. montana) are indigenous to China, 

 but the varnishes made from the oil were found to be so valuable 

 that the Americans introduced it to Florida in 1905. In 1927 the 

 Empire Marketing Board provided a grant to Kew to send seed 

 to suitable Empire centres and to pay a research worker to experi- 

 ment on the properties of Empire-grown tung oil and residue as 



