Medullary Bundles - Internal Anatomy
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Section by Sheila M. Hayden; photomicrograph by W.
John Hayden; secondary phloem development (blue) in medullary
bundles of moderately mature stem (below the inflorescence region).
Section by Sheila M. Hayden; photomicrograph by W.
John Hayden; secondary xylem from medullary bundles filling the
pith region of a mature late-season stem (below the inflorescence
region).