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Aerenchyma in stem cross section of a typical wetland plant. Aerenchyma or aeriferous parenchyma [1] or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. [2]
This constitutes the so-called capsule of the space. Each lacuna is generally occupied by a single cell, but during the division of the cells, it may contain two, four, or eight cells. Lacunae are found between narrow sheets of calcified matrix that are known as lamellae (/ l ə ˈ m ɛ l i / lə-MEL-ee).
The plant fossils found show many structural and anatomical adaptations to an aquatic environment, including a reduced vascular system, aerenchyma in tissues (air spaces to provide buoyancy), and protoxylem lacunae surrounded by a ring of cells with thickened inner walls.
Parenchyma is a versatile ground tissue that generally constitutes the "filler" tissue in soft parts of plants. It forms, among other things, the cortex (outer region) and pith (central region) of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds.
The inner cortex is the narrowest and consists of small parenchyma cells; secretory cells, lacunae, and various sclerotic cells also can be found in this section. The middle cortex is larger and in turn consists of larger parenchyma cells.
The SBA was created on July 30, 1953, by Republican President Eisenhower with the signing of the Small Business Act, currently codified at 15 U.S.C. ch. 14A.The Small Business Act was originally enacted as the "Small Business Act of 1953" in Title II (67 Stat. 232) of Pub. L. 83–163 (ch. 282, 67 Stat. 230, July 30, 1953); The "Reconstruction Finance Corporation Liquidation Act" was Title I ...
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The leaves are narrow and linear, translucent, mid or olive green, usually 20–50 mm long × 0.8–1.4 mm wide, but rarely up to 100 mm long and 1.9 mm wide. The midrib often lacks lacunae (transparent areas either side of the midrib) either side of it, and if present, lacunae are restricted to the lower half of the leaf. [5]