INTERNAL GAS-TRANSPORT IN TYPHA-LATIFOLIA L AND TYPHA-ANGUSTIFOLIA L .1. HUMIDITY-INDUCED PRESSURIZATION AND CONVECTIVE THROUGHFLOW

The internal gas transport in the shoots of the cattails, Typha latifolia L. and Typha angustifolia L., occurs principally via pressurized convective throughflow of gases. Static pressure differentials of up to 350 Pa relative to ambient for T. latifolia and 570 Pa for T. angustifolia were found to be generated mainly by humidity-induced diffusion at ambient temperatures of 15-25 degrees C. Thermal transpiration did not contribute significantly to the internal pressurization. Convective gas flow rates of up to 8 cm(3) min(-1) for T. latifolia and 3.5 cm(3) min(-1) for T. angustifolia were recorded from cut rhizomes. Internal pressurization and convective throughflow rates were highest at high ambient temperature and low ambient relative humidity. Light did not affect pressurization in T. latifolia, whereas pressurization and convective gas flows were lower in the light than in the dark in T. angustifolia, probably as a consequence of stomatal movements. A layer of closely packed mesophyll cells located just below the palisade parenchyma of the leaves is probably the porous partition responsible for the pressurization, but stomata with tortuous pathways may also be involved. Under identical environmental conditions the ventilation capacity of T. angustifolia is about twice as high as that of T. latifolia indicating that root aeration of the former may be more efficient.