Beijerinck confirmed the findings of Ivanovski. He showed that the tobacco mosaic virus would diffuse through agar. "Like Ivanovsky before him and Adolf Mayer, predecessor at Wageningen, Beijerinck could not culture the filterable infectious agent; however, he concluded that the agent can replicate and multiply in living plants. He named the new pathogen virus to indicate its non-bacterial nature. Beijerinck asserted that the virus was somewhat liquid in nature, calling it "contagium vivum fluidum" (contagious living fluid). It was not until the first crystals of the tobacco mosaic virus (TMV) obtained by Wendell Stanley in 1935, the first electron micrographs of TMV produced in 1939 and the first X-ray crystallographic analysis of TMV performed in 1941 proved that the virus was particulate" (Wikipedia article on Martinus Beijerinck, accessed 5-2020).

Translation in Phytopathological Classics, 1942, No. 7.

Discovery of nitrogen fixation, the process by which diatomic nitrogen gas is converted to ammonium ions and becomes available to plants. Bacteria perform nitrogen fixation, dwelling inside root nodules of certain plants (legumes). In addition to having discovered a biochemical reaction vital to soil fertility and agriculture, Beijerinck revealed this archetypical example of symbiosis between plants and bacteria.