Brown made important contributions to botany by using the microscope. He made an early description of the cell nucleus and cytoplasmic streaming. He saw Brownian motion. He did early work on plant pollination and fertilisation. He was the first to recognise the difference between gymnosperms and angiosperms. He did some of the earliest studies in palynology. He also made numerous contributions to plant taxonomy. He identified plant families which are still accepted today.