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 latifo lia L. and Typha angustifolia L., occurs principally via pressurized c onvective throughflow of gases. Static pressure differentials of up to 350 Pa relative to ambient for T. latifolia and 570 Pa for T. angusti folia 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. Convectiv e 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. Intern al pressurization and convective throughflow rates were highest at hig h ambient temperature and low ambient relative humidity. Light did not affect pressurization in T. latifolia, whereas pressurization and con vective gas flows were lower in the light than in the dark in T. angus tifolia, probably as a consequence of stomatal movements. A layer of c losely packed mesophyll cells located just below the palisade parenchy ma of the leaves is probably the porous partition responsible for the pressurization, but stomata with tortuous pathways may also be involve d. Under identical environmental conditions the ventilation capacity o f T. angustifolia is about twice as high as that of T. latifolia indic ating that root aeration of the former may be more efficient.