Seasonal Variation of the Essential Oil, Valerenic Acid and Derivatives, and Valepotriates in Valeriana officinalis Roots and Rhizomes, and the Selection of Plants Suitable for Phytomedicines - Bos, Rein; Woerdenbag, Herman J; van Putten, Freeke M S; Hendriks, Henk; Scheffer, Johannes J C (Planta Medica, 1998)