Comparable studies of plants in the Rijksprentenkabinet, Amsterdam, the Collection of the Stichting Genootschap Cornelis Ploos van Amstel-Knoef and the municipal archives, Tilburg may be dated to 1806-8 (E. Bergvelt, M. van Boven, J.A. Knip 1777-1847, The Hague, 1977, nos. 14-5 and 18 respectively). These studies are reminiscent of the work of Knip's German contemporaries, Caspar David Friedrich (1774-1840) and Heinrich Kolbe (1772-1836).