Discrete Mathematics Problems Arising in Digital Communication

An upwardly open receptacle for plants includes a bottom wall, a reservoir adjacent the receptacle and having an opening at the bottom in communication with a membrane in the bottom of the receptacle, and a compartment in operative relation with the reservoir. The compartment has a first conduit communicating the atmosphere with a first location within the compartment, and a second conduit communicating a second location within the compartment with the location in the reservoir adjacent the lower region of the receptacle. The second location is above the first location. The compartment is adapted to contain liquid to a level between the two locations, and is sealed from the atmosphere except for the first-mentioned conduit.