Woody Dicot Stem Periderm in One Year Sambucus (35922606845)

Författare/Upphovsman:

Berkshire Community College Bioscience Image Library

Kreditera:

Woody Dicot Stem: Periderm in One Year Sambucus

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https://sewiki.info/b/9db7c

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Wikimedia Commons

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3264 x 1840 Pixel (1040239 Bytes)

Beskrivning:

cross section: Sambucus stem magnification: 400x

A one-year stem of Sambucus demonstrates the differentiation of the upper cortex in tissues of the periderm.

During the first year of growth the epidermis is stretched laterally by the expansion of secondary xylem, phloem and cambium. The epidermis is replaced by a protective secondary zone of cork rich periderm. Continual growth of the periderm keeps up with that of underling tissues allowing it to replace the functions of the degrading epidermis.

The outermost layer of periderm consists of layers of cork cells, the phellem, which produce the waterproofing substance suberin. Cork cells are dead at maturity. Deep to the phellem is a layer of living green stained cork cambium or phellogen and just beneath that layers of cork parenchyma or phelloderm.  Many cells in the periderm contain dark staining tannins.

In certain areas the cork cambium over produces cork cells, resulting in the formation of ridges and deep cracks in the periderm. These deep fissures, or lenticels, permit gas exchange with tissues under the periderm.

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CC0

Licensvillkor:

Creative Commons Zero, Public Domain Dedication