Antagonistic effect of alkaloids and saponins on bioactivity in the Quinine Tree (Rauvolfia Caffra Sond.): further evidence to support biotechnology in traditional medicinal plants - Milugo, T; Omosa, L; Ochanda, J; Owuor, B; Wamunyokoli, F; Oyugi, J; Ochieng, J (BMC Complement Altern Med, 2013)