PURPOSE: To obtain the titled vessel enabling the cultivation of a tropical ornamental foliage plant even in cold season, by applying a double-wall structure to at least a part of the side wall or a bottom wall and sealing a thermostatic heater composed of an emulsion and an electrode in the space in the double-wall structure.

CONSTITUTION: The front face of a side wall 12 of a plant vessel 10 has a double-wall structure composed of an inner wall 14 and an outer wall 16 and the double-wall structure contains a pair of cylindrical electrodes 18, 18 placed facing with each other. An emulsion 20 of water and an oleophilic fluid is sealed in the space around the electrodes. The emulsion acts as a heater at or below the phase-transition temperature by passing electric current and keeps a constant temperature near the phase-transition temperature.