Diffusion pathway for oxygen into highly thermogenic florets of the arum lily Philodendron selloum

Thermogenic inflorescences of some arum lilies have the highest rates of respiration known among plants. Peak rates of oxygen consumption in the sterile male florets of Philodendron selloum Koch exceed 0.3 micromol x s(-1) x g(-1) when the inflorescence warms to 38 degrees C. This study describes the morphology of the oxygen diffusion pathway between the atmosphere and the parenchymal cells of the florets. Dimensions of the florets, stomata, interstitial gas network, and cells provide data for diffusion models of the PO2 profiles at each level of the 'oxygen cascade'. The lowest calculated PO2 of 4.7 kPa (35 mmHg) at the axis of the thickest part of the floret indicates that maximum respiration does not reach the point of diffusion-limitation, confirming earlier physiological measurements of the dependence of oxygen consumption rate on environmental PO2. Adequate aeration of all cells is achieved by appropriate floret size, despite a stomatal density less than 5%, and interstitial gas fraction less than 2%, of values commonly found in leaves.