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Shoot Apex Organization and Origin of the Rhizome-Borne Roots and Their Associated Gaps in Dennstaedtia cicutaria

Dennis Wm. Stevenson
American Journal of Botany
Vol. 63, No. 5 (May - Jun., 1976), pp. 673-678
Stable URL: http://www.jstor.org/stable/2441830
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Shoot Apex Organization and Origin of the Rhizome-Borne Roots and Their Associated Gaps in Dennstaedtia cicutaria
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Abstract

The shoot apex of Dennstaedtia cicutaria consists of three zones-a zone of surface initials, a zone of subsurface initials, and a cup-shaped zone that is subdivided into a peripheral region and central region. A diffuse primary thickening meristem, which is continuous with the peripheral region of the cup-shaped zone, gives rise to a broad cortex. The roots occurring on the rhizomes are initiated very near the shoot apex in the outer derivatives of the primary thickening meristem. The roots that occur on the leaf bases also differentiate from cortical cells. Eventually, those cortical cells situated between the newly formed root apical cell and the rhizome procambium (or leaf trace) differentiate into the procambium of the root trace, thus establishing procambial continuity with that of the rhizome or leaf trace. Parenchymatous root gaps are formed in the rhizome stele and leaf traces when a few of their procambial cells located directly above the juncture of the root trace procambium differentiate into parenchyma. As the rhizome procambium or leaf trace continues to elongate, the parenchyma cells of the gap randomly divide and enlarge, thus extending the gap.

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