File:Gymnosperm Stem Secondary Growth in Four Year Pinus (35498052724).jpg
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原始文件 （3,264 × 1,840像素，文件大小：2.56 MB，MIME类型：image/jpeg）
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摘要
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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. |
| 日期 | |
| 来源 | Gymnosperm Stem: Secondary Growth in Four Year Pinus |
| 作者 | Berkshire Community College Bioscience Image Library |
许可协议
 
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本作品采用知识共享CC0 1.0 通用公有领域贡献许可协议授权。 |
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这幅图片原始出处为Flickr的https://flickr.com/photos/146824358@N03/35498052724 ，作者为bccoer 。经机器人FlickreviewR 2在2018年6月22日审查后确定为采用cc-zero的协议授权使用。 |
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| 日期/时间 | 缩略图 | 大小 | 用户 | 备注 | |
|---|---|---|---|---|---|
| 当前 | 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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