File:Gymnosperm Stem Secondary Growth in Four Year Pinus (35498052724).jpg
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原始檔案 （3,264 × 1,840 像素，檔案大小：2.56 MB，MIME 類型：image/jpeg）
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摘要
| 描述 |
cross section: Pinus stem magnification: 100x The vascular cylinder or stele in young stems consists of a ring of vascular bundles interspaced with medullary rays of parenchyma cells. Seasonal activity of the cambium replaces the isolated vascular bundles with well-defined annual rings of secondary phloem and xylem. Xylem is endarch with protoxylem found towards center of the stem and younger metaxylem towards the periphery of the stem. Protoxylem consists of annular and spiral tracheids with only tracheids found in metaxylem. True xylem vessels are lacking. Because of the greater production of xylem, the vascular cylinder is dominated by radially arranged rays of secondary xylem interspaced with medullary rays of parenchyma cells. Conspicuous resin ducts are present throughout the xylem. Phloem is endarch but annual growth the of stem makes it difficult to distinguish between older protophloem to the periphery and younger metapholem towards center of the stem. Phloem lacks companion cells, consisting entirely of sieve tubes and phloem parenchyma. Medullary rays in the secondary phloem include protein rich albuminous cells. |
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| 來源 | Gymnosperm Stem: Secondary Growth in Four Year Pinus |
| 作者 | Berkshire Community College Bioscience Image Library |
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這幅圖片原始出處為Flickr的https://flickr.com/photos/146824358@N03/35498052724 ，作者為bccoer 。經機器人FlickreviewR 2在2018年6月22日審查後確定為採用cc-zero的協議授權使用。 |
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| 日期/時間 | 縮圖 | 尺寸 | 使用者 | 備註 | |
|---|---|---|---|---|---|
| 目前 | 2018年6月22日 (五) 23:54 | | 3,264 × 1,840（2.56 MB） | Meisam | Transferred from Flickr via #flickr2commons |
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