Unpublished paper, 'On the colour of leaves of plants and their autumnal changes' by Arthur Hill Hassall Hassall writes: 'Chlorophyll, the name given by botanists to the green colouring matter of the leaves of plants, is not, as hitherto obtained, a simple substance, but is composed, in part at least, of constituents whcih are non essential to its green colour, though iron is deemed to be an indispensible ingredient.' Hassall shares experimental observations on chlorophyll. Annotations in ink throughout. Subject: Biology / Botany Received 21 June 1892. Communicated by [Thomas Henry] Huxley. 1892