by Uitto, J I
Published in African study monographs (01.12.1992)

by Sokari-george, E, Emeruem, J O, Dimkpa-harry, S H
Published in African study monographs (01.12.1991)

by Dimkpa-harry, S H
Published in African study monographs (01.10.1991)

by Oyono, P.R
Published in African Study Monographs (2005)