The Petri dish (photo above by “Lilly M”) has been of great benefit to microbiologists wishing to culture bacteria. The Petri dish was invented by the German microbiologist Julius Petri (1852–1921), a colleague of Robert Koch. In 1887, Petri wrote a paper describing how bacteria could be grown on a layer of gelatin in such a dish.
The use of agar in Petri dishes dates from 1881, when Fanny Hesse, wife of Walther, suggested its superiority to gelatin. Frau Hesse apparently used agar for cooking, as a result of having friends from what was then the Dutch East Indies (“agar” is a Bahasa word).
Petri dishes are also useful for studying reactions such as the Belousov–Zhabotinsky (BZ) reaction in thin liquid layers: