A Petri dish is a shallow cylindrical glass or plastic lidded dish that biologists use to culture cells. It is named after its inventor, German bacteriologist Julius Richard Petri. Gelatin is a colorless and flavorless food product made from collagen obtained from animal body parts. AGAR is a gelatinous substance derived from red algae, which is used as a gelling agent in the preparation of Petri dish gelatin.