The credit of formulating cell theory is usually credited to two scientists that are Matthias Schleiden and Theodor Schwann but Rudolf Virchow was a well-known scientist who is known for his contribution to the cell theory.
In 1855 in his publication the statements were based on the observation about the cells that arise from pre-existing cells which he called Omnis cellula e cellula. Therefore after this publication, all accepted that new cell comes from the old cell which was early thought that new cells comes from fluid known as blastema.
So Rudolf Virchow contributed in the cell theory by popularizing the last theory of cell theory that says that new cells come from pre-existing cells.
I would start on Evaporation. I will then have to go through condensation, then precipitation, then a surface runoff then into groundwater which will start the evaporation process all over again :)
