What was Robert brown looking at through a microscope when he found evidence of the 1827 specific concept named in his honor?

In 1827, Robert Brown was examining pollen grains from the orchid Orchis morio through a microscope when he observed the random, jittery movement of these particles. This phenomenon, later known as Brownian motion, demonstrated the erratic movement of microscopic particles suspended in a fluid, which is caused by collisions with the molecules of the surrounding medium. Brown's observations laid the groundwork for the understanding of particle dynamics in fluids and contributed to the development of kinetic theory in physics.