crossing to England, but he had great doubts and did not know what to advise. William Bentinck called him the most sensitive man in the world. Of the other three burgomasters – Jean Appelman (a merchant trading with France), Johannes Hudde and Cornelis Geelvinck – Geelvinck openly opposed the enterprise and Appelman was not trusted by the prince and thus was not informed. After the crossing went ahead, Witsen went to London in the next year to find a way of meeting the costs of 7,301,322 guilders the city of Amsterdam had incurred in supporting it. William offered to knight him as a baronet, but the modest Witsen refused. Already in his youth Witsen started to collect Siberian curiosities and artworks, gathering corals, lacquer, books, paintings, weapons, porcelain, insects, seashells, stuffed animals and precious stones into his house on Herengracht on the Golden Bend. As mayor, he was a patron of the arts and sciences and maintained contacts with German scholars, such as Leibniz. He corresponded with Antonie van Leeuwenhoek, discovering tiny creatures under his microscope. In 1698 Willem de Vlamingh offered him two seashells from New Holland (Australia) and Witsen offered the drawings to Martin Lister. Witsen, who had invested in the journey, was disappointed that the men had been more interested in setting up trade than in exploring. Witsen tried to introduce coffee plants from Batavia via Amsterdam to countries in South America. Boerhaave estimated that Witsen had put together a collection of more than 1500 paintings of plants that came to be known as the Codex Witsenii and were for the greater part of plants growing in and around the Cape Peninsula. These passed into the custody of Caspar Commelin, Professor of Botany at the Athenaeum Illustre and working in the Hortus Botanicus. After Commelin's death, they were passed to Johannes Burman, inspiring him to produce Rariorum africanarum plantarum in 1738-9. On Burman's death in 1779, his effects passed to his son, Nicolaas Laurens Burman. After his death in 1793, his effects, including the Codex, were sold by auction in 1800, disappearing from the records. Witsen had contact with the painter Jan de Bray over a plan to improve the city's water supply, and helped the artist Cornelis de Bruijn, who needed contacts in Egypt and Russia – indeed, it was probably Witsen who encouraged De Bruijn to make drawings of Persepolis, to show to the Royal