The generation of a humidity-induced convective volume flow of air across a porous asymmetric membrane is analyzed theoretically in terms of linear laws of the thermodynamics of irreversible processes. The theoretical analysis is the basis of an experimental study of humidity induced convection (HIC) in a model system. The experimental results can be described consistently in terms of the theoretical concept. It is well established in plant physiology that HIC is responsible for the transport of oxygen (air) within certain plant species growing in wetlands.