Abstract: A multi-cell tray comprises a base having an upper wall and side walls defining an outer periphery, with a plurality of cells for receiving test media in the upper wall, and a removable cover on the base having side walls depending downwardly from a top wall, with the side walls of the base and cover being spaced apart to define a passageway for gas to enter the tray. A baffle encompasses the cell area of the base and extends upwardly from the upper wall of the base to deflect incoming gas upwardly away from the level of the cells, with passageways uppermost of the baffle for allowing the deflected gas to enter a chamber above the cells defined between the spaced upper walls of the base and cover.