Cytotoxicity of Flavonoids and Sesquiterpene Lactones from Arnica Species Against the GLC4 and the COLO 320 Cell Lines - Woerdenbag, Herman J; Merfort, Irmgard; Paßreiter, Claus M; Schmidt, Thomas J; Willuhn, Günter; van Uden, Wim; Pras, Niesko; Kampinga, Harm H; Konings, Antonius W T (Planta Medica, 1994)