Fig. 1.

Sketches of the freshwater, rosette species L. dortmanna (right) and the marine seagrass Z. marina (left). Average values are shown for percentage dry weight (W, % of plant d. wt), surface area (A, cm² g⁻¹ plant d. wt), gas volume (V_a, cm³ g⁻¹ plant d. wt) and cross-sectional areas of lacunae (A_a, mm² g⁻¹ plant d. wt) normalized to total plant dry weight. Cross-sectional areas of lacunae were determined as the summed cross-sectional area for all leaves and roots at the mid-point of their length normalized to the dry weight of the entire plant, thereby describing the cross-sectional area available for longitudinal diffusive transport of gases for a standard plant dry weight. Mean values of 11 individuals of L. dortmanna (Sand-Jensen and Prahl, 1982) and nine individuals of Z. marina. Note the 10-fold difference in scale between the two sketches.