January 26, 1792 (a Thursday)

Robert Brown as a young man.

On this date, the Scottish botanist Robert Brown read his first scientific paper entitled “The botanical history of Angus“, to the Edinburgh Natural History Society, although it was never published in print in his lifetime.  He was born on 21 December 1773, so that he was but a little over eighteen when he read this essay.  Later in life, he made important contributions to science largely through his pioneering use of the microscope.

In 1827, while examining pollen grains under a microscope, Brown observed minute particles within vacuoles in the pollen grains executing a continuous jittery motion. He then observed the same motion in particles of dust, enabling him to rule out the hypothesis that the effect was due to pollen being alive. Although Brown did not provide a theory to explain the motion, and Jan Ingenhousz already had reported a similar effect using charcoal particles in German and French publications of 1784 and 1785, the phenomenon is now known as “Brownian motion.”  [In 1905, Albert Einstein postulated that Brownian motion was direct evidence of molecular action, thus supporting the atomic theory of matter.]

The cell.

Robert Brown is perhaps most famous for identifying a structure within cells that he named the “nucleus” in a paper read to the Linnean Society of London  in 1831 and published in 1833. Furthermore, he suggested that the nucleus may be an essential component of the cell. He discovered the nucleus while studying orchids microscopically, in the cells of the flower’s outer layer. The nucleus had been observed before, perhaps as early as 1682 by the Dutch microscopist Leeuwenhoek, and Franz Bauer had noted and drawn it as a regular feature of plant cells in 1802, but it was Brown who gave it the name it bears to this day (while giving credit to Bauer’s drawings). Neither Bauer nor Brown thought the nucleus to be universal, and Brown thought it to be primarily confined to Monocotyledons.

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