Observations on the Gaseous Exchanges which take place betweenMenyanthes TrifotiataL. and its Environment

The exchange of gases between whole plants of Menyanthes and their environment has been investigated. When a 45 cm. rhizome is surrounded by an almost oxygen-free environment, leaving the leafy shoot exposed to air, some oxygen passes right through the rhizome, and the QO2 of the plant is significantly reduced. Analyses of gases from the air-space system show that oxygen concentrations fall and CO concentrations rise when plants are transferred to, and maintained under conditions like these. Oxygen concentrations show a linear gradient from top to bottom of the plant, whilst the reverse is true for CO2. The main barrier to gas movement is shown to lie within the air-space system of the rhizome, and the number of leaves present on the plant has little effect upon the oxygen content of the internal atmosphere. It is shown that as the concentration of CO2 increases in the air space system of a rhizome, so the consumption of oxygen falls off, thus allowing more oxygen to pass through the rhizome to more distal regions. Variation in the seasonal activity of the plant is discussed in relation to these find ings and to reported studies on the respiration of rhizome-tissue slices. Deter minations of respiration on tissues such as these are held to be less meaningful if carried out according to the ‘direct’ method. The biological significance of these features is discussed.