YAMS AND SWEET POTATOES 159 



has been harvested is rarely used for Guinea corn ; the 

 succeeding crop being usually cotton, with the applica- 

 tion of manure. In the Nupe country, near Bida, 

 cassava is frequently employed as a shade crop for 

 onions ; in this case being planted around the onion 

 beds and obtaining the benefit of the high state of cul- 

 tivation, manuring and irrigation which is applied to 

 that crop. Cassava grown under these conditions is 

 planted twenty days later than the onions, and is 

 pulled up a month later. 



The pagan tribes of Zaria, and the other provinces 

 where they are in greater numbers, do not seem to 

 plant cassava. The Haussa name given to the plant is 

 " Rogo." 



YAMS (Dioscorea sativa, etc.). These climbers are 

 commonly grown in the moist valley of the Niger and in 

 the Yoruba country of Ilorin, but are rare and only an 

 irrigated crop in the more northern countries. Where 

 they are seen, they are planted from root eyes upon 

 high mounds with ditches dammed to retain the water 

 between them, and, until the plant has grown up as a 

 trailer upon the ground, some feet in length, no supports 

 are put in. At this time, however, the straw covers, 

 which it is customary to place on the apex of the 

 yam mounds, are removed and an elaborate system 

 of stakes, to the top of each of which strings are 

 tied and conducted to the ground near the growing 

 plant, are put in, and the plants to the number of 

 four or more are trained to grow towards the top of 

 each stake. 



The large white yam is chiefly grown, and is called 

 in Haussa " Doya." Yams attain large dimensions in 

 the damp localities, but are small in the drier places. 



Colocasia antiquoriim, called by the Haussas " Kamu," 

 is usually referred to as the koko yam and is rarely 

 grown. A few may be seen in the wet localities and 

 near Zaria, where they are planted in swamps upon 

 high mounds or ridges. 



SWEET POTATOES. This crop is grown everywhere, 

 and is nearly always unmanured. It is said that it forms 

 the occupant of the land upon which Guinea corn and 

 millet are repeatedly grown in some parts of the Kano 

 district in the second and eighth year i.e. twice in a 



