Light micrograph of spirally-thickened xylem elements in a longitudinal section of the stem of a castor oil plant, Ricinus sp. Xylem tissue is responsible for the upward transport of water and solutes in the plant. The spiral bands provide reinforcement for its tubes. The first cells to be formed were those on the right, and elongation of the stem during growth has pulled out the spiral coils. Moving left across the picture, the spirals show a progressive reduction in spacing because the cells were formed later and have consequently undergone less stretching. Magnification unknown.
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