File:Gymnosperm Leaves Casparian Strip in Two Needle Pinus (36501132825).jpg
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摘要
描述Gymnosperm Leaves Casparian Strip in Two Needle Pinus (36501132825).jpg |
cross section: Pinus needle magnification: 400x Pinus needles may be circular, semicircular or triangular in cross section and are structurally adapted to tolerate xeric stress and freezing. A single layered epidermis of lignified cells is covered by a heavy waxy cuticle. Numerous sunken stomata are scattered over the entire epidermal surface. They are bounded by pairs of subsidiary cells, and open internally to a substomatal cavity and externally to a respiratory cavity or vestibule. The underlying hypodermis consists of several layers of thick-walled sclerenchyma, particularly well-developed at ridges. Deep to the hypodermis lies an undifferentiated photosynthetic mesophyll. Cells are distinctively lobed with infolded cell walls. They are filled with chloroplasts and starch grains that may be difficult to see because of an accumulation of dark staining tannins and resins. A few resin canals can be seen close to the hypodermal side of the mesophyll. A central vascular bundle is wrapped in a single layered endodermis with a well-defined casparian strip whose end walls may become heavily suberized with age. Deep to the endodermis lies a multilayered parenchymous pericycle with two vascular bundles separated by an often indistinct band of sclerenchymal cells. The pericycle also contains transfusion tissues of protein rich albuminous cells which abut and assist the phloem in the transport nutrients and elongated tracheidal cells which abut and assists the xylem in the transport of water. Most species possess two conjoint, collateral vascular bundles, surrounded and supported by the tissues of the pericycle. Xylem tracheids lie towards the adaxial surface and phloem sieve tubes towards abaxial surface of the leaf. Xylem vessels and fibers, and phloem companion cells are absent in Gymnosperms. While vascular bundles are closed some cambium may persist near the base of the needle. Visit the BCC Bioscience Image featuring the Microscopic World of Plants. <a href="http://www.berkshirecc.edu/biologyimages" rel="nofollow">www.berkshirecc.edu/biologyimages</a> |
日期 | |
來源 | Gymnosperm Leaves: Casparian Strip in Two Needle Pinus |
作者 | Berkshire Community College Bioscience Image Library |
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2018年6月22日
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創作作者 Chinese (Hong Kong) (已轉換拼寫)
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著作權狀態 繁體中文 (已轉換拼寫)
保有知識產權並由其所有者公開於公有領域 繁體中文 (已轉換拼寫)
10 2 2014
檔案來源 Chinese (Taiwan) (已轉換拼寫)
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目前 | 2018年6月22日 (五) 23:56 | 3,264 × 1,840(1.17 MB) | Meisam | Transferred from Flickr via #flickr2commons |
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資料產生的日期時間 | 2014年2月10日 (一) 11:00 |
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使用軟體 | Windows Photo Editor 10.0.10011.16384 |
檔案修改日期時間 | 2017年8月11日 (五) 09:41 |
數位化的日期時間 | 2014年2月10日 (一) 11:00 |
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