Abstract: A vertically elongated anaerobic jar of polygonal horizontal cross-section is formed of transparent panels of a width somewhat greater than the diameter of a petri dish or plate. A (preferably removable) similarly shaped hollow body is co-axially disposed in the jar to define with facing transparent panels, radially shallow compartments to receive a plurality of petri dishes stacked on edge, so that their contents can be viewed through the transparent panels. The inner body may be provided with horizontal channel elements spaced to hold a petri dish on edge and bottomed against the panels of the inner body. The jar is conventionally provided with an air-tight cover, a clamp device and a container for catalyst pellets.