Robert Brown (1773-1858), Scottish botanist. Brown spent years working on plant taxonomy, establishing the classification of two major divisions of plants (gymnosperms and angiosperms). He also observed an essential part of living cells, which he named the nucleus. His famous 1827 observation of erratic motion by pollen grains in water (Brownian motion) was later explained as evidence for the existence of molecules. Brown became the first Keeper of the Botanical Department at the British Museum. This engraving is of a portrait by Henry William Pickersgill, presented to the Linnean Society, of which Brown was Vice-President.