Bogbean stem. Light micrograph of a cross-section through the stem of a bogbean plant (Menyanthes trifoliata), showing its internal structure. Bogbeans live in shallow water in boggy places, with leaves that split into three and float on the surface of the water. The stem is supported by the water and therefore needs little vascular tissue (dark green circles) to support it. There is a lack of oxygen in the water of boggy places so the stem tissue (aerenchyma) is instead spongy in nature, with large air spaces found between a network of cells. During photosynthesis these become filled with oxygen, which is later used for respiration. The air filled stem also helps keep the plant buoyant in the water.