In 1890 Russian botanist Dmitri Ivanovsky was commissioned to study a disease destroying tobacco plants in Crimea. Filtering the sap from affected plants, Ivanovsky discovered in 1892 the presence of a small parasitic microorganism invisible under great magnification—a virus—which he thought was a minuscule bacterium. In 1898 Dutch microbiologist Martinus W. Beijerinck became the first person to recognize viruses as reproducing entities distinct from other organisms.