THE MECHANISM OF THERMAL TRANSPIRATION (EQUALS THERMAL OSMOSIS)

Floating-leaved aquatic plants have acquired a convective gas-throughf low system to supply oxygen from the atmosphere to their roots and rhi zomes growing in anoxic sediments of shallow lakes and are dependent u pon an efficient internal aeration. Tissue layers with minute pores in side the newly-emergent leaves, separating the aerenchyma of the leave s from the ambient atmosphere, create a pressurised ventilation by bot h the physical effects of hygrometric diffusion (humidity-induced diff usion) and thermal transpiration (thermal osmosis). In mature leaves, these pores are dilated to such an extent that free-flow of gas throug h this partition is possible. Therefore, the air, which moves into the young leaves (influx leaves) along humidity and temperature gradients , causing pressurisation in the aerenchyma, flows through the continuo us intercellular space system and the mature leaves (efflux leaves) ba ck to the atmosphere. Taking into account theoretical considerations a nd the physical background and anatomical requirements of the leaves, it is explained how the pressurised ventilation, based on thermal tran spiration, operates in the aquatic plant during the growing season as soon as two floating leaves have been developed.