Gas Exchange betweenEquisetum limosumand its Environment

SUMMARY Equisetum limosiim grows in standing water. Its perennating rhizomes ramify in the bottom mud, which is a markedly oxygen-deficient medium. During the summer months aerial shoots are present and extend above the surface of the water to a height of about i m. The concentration of oxygen in the internal atmosphere of plants in the field decreases progressively from the stem to the perennating rhizomes. There is a reverse gradient of carbon dioxide concentra tions. The structure of the nodal diaphragms of the aerial stem is described and the progressive occlusion of the pores of the diaphragms between May and November is demonstrated. This occlusion of the diaphragms has been correlated with a reduction in the ease of gaseous diffusion along lengths of aerial stems. Oxygen is present in the rhizomes throughout the winter, despite the fact that the dead aerial stems have broken off and the stumps have been submerged by the rise in water level, thus isolating the rhizome from atmospheric oxygen. The results are discussed in relation to the ability of the plant to grow in an oxygen-deficient environment.