1. Trees and shrubs, hardy in the British isles.
2. THE ORCHID PAINTINGS OF JOÃO BARBOSA RODRIGUES (1842–1909)
3. Director's Correspondence. JDH/2/16/67a.Letter 23 Aug. 1880.
4. Darwin Correspondence Project Letter no. 5483 accessed on 8 June 2022
5. Darwin Correspondence Project Letter no. 6907 accessed on 10 March 2022