As anyone who uses Google knows, today they recognized Julius Richard Petri's 161st birthday. A Petri dish, aka a cell culture dish, is a shallow round dish with a raised edge, often used by microbiologists to grow bacteria or other microorganisms (here in LEGO by MorsLEGO). Usually the dish is partially filled with a warm liquid mixture of agar and nutrients. After it cools the agar becomes a semi-solid gelatin that is an appropriate surface for growing the bacteria, which can be studies as they grow.
In a fun twist, artist Darlene Charneco made Podland Petri.