Abstract: A collapsible terrarium assembly which is inflatable to assume a desired configuration for protectively housing a plant or other organic material in a controlled environment adapted to promote plant growth or to stimulate organic activity. The structure is constituted by a disc-like base and a replaceable dome attachable thereto by means of a coupling ring. The dome is formed by a flexible plastic envelope whose rim is provided with an annular skirt that is interposed between the coupling ring and the base to define a hermetically-sealed enclosure. The envelope is provided with a two-way valve, which in one position makes it possible to exhaust the air from the enclosure, and in another position to inflate the dome with an inert gas to create a controlled environment.