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The Bundle Sheath Extension in Leaves of Dicotyledons
Robert B. Wylie
American Journal of Botany
Vol. 39, No. 9 (Nov., 1952), pp. 645-651
Published by: Botanical Society of America, Inc.
Stable URL: http://www.jstor.org/stable/2438370
Page Count: 7
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Bundle sheath extensions are vertical sheets of colorless cells, usually developed on opposite sides of certain lesser veins in leaves of many dicotyledons. They are always connected with the bundle sheath and generally extend to both epidermal layers. Together with the included vein, opposite extensions constitute a vertical partition in the lamina which extends along given vein segments and at their junctions unite laterally to form contiguous chambers of the blade, which enclose the chlorenchyma. The present survey, using both transverse and paradermal sections of the blade, covered leaves of 348 species of dicotyledons, from Iowa, southern Florida and North Island, New Zealand; 210 of these carried bundle sheath extensions. Their structure, occurrence and distribution in the leaves are described. These sheath extensions were of most frequent occurrence in the thin, northern deciduous leaves and least common in the thick, broad-leaved evergreen leaves of New Zealand. The present study indicates that these sheath extensions are of functional importance to the leaf and there is evidence that they share in the extravascular translocation of the blade. Two leaf patterns were found among dicotyledons in each region, depending upon whether bundle sheath extensions were present or lacking in the blade. Mean measurements for all species of both divisions showed that the divisions lacking sheath extensions had thicker blades with increases in the amount of the several blade tissues. It seems probable that the leaves of both patterns will be found in all regions favorable for the growth of dicotyledons.
American Journal of Botany © 1952 Botanical Society of America, Inc.