transverse or cross section: Pinus stem magnification: 400x iron-alum hematoxylin and safranin stain Berkshire Community College Bioscience Image Library Well defined annual rings of large diameter spring wood and smaller diameter autumn wood are composed entirely of narrow, relatively thin walled tracheids. The lumen of many tracheids is crossed by branched trabeculae. Tracheid side walls contain large circular bordered pits that function to move water from tracheid to tracheid while preventing air flow from embolized tracheids. Gymnosperms like Pinus rely entirely on tracheids for water flow and mechanical support. True xylem vessels and wood parenchyma are lacking. While fibers are generally absent older stems may contain some fiber tracheids. Xylem rays are uniseriate and composed of clear, thin walled parenchyma cells. Technical Questions:[email protected]
tangential section: Pinus stem magnification: 400x iron-alum hematoxylin and safranin stain Berkshire Community College Bioscience Image Library Gymnosperms like Pinus rely entirely on tracheids for water flow and mechanical support. True xylem vessels and wood parenchyma are lacking. While fibers are generally absent older stems may contain some fiber tracheids. The uniform wood of Pinus consists almost entirely of longitudinally oriented bands of narrow, pale staining tracheids interrupted by short bands of horizontally oriented xylem rays. Xylem rays, usually one cell thick and a few cells high, are composed of clear, thin walled parenchyma cells. The lumen of many tracheids is crossed by branched trabeculae. Tracheid side walls contain large circular bordered pits that function to move water from tracheid to tracheid while preventing air flow from embolized tracheids. The membrane of each bordered pit is marked by a pale, thin, porous outer margo and a thicker, darker, inner torus. Technical Questions:[email protected]
cross section: Liriodendron stem magnification: 400x Berkshire Community College Bioscience Image Library During the first year of growth the underling activity of the cork cambium begins to replace the cutinized epidermis and outer cortical tissues with a protective layer of cork rich periderm. 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 cork cambium or phellogen and just beneath that layers of cork parenchyma or phelloderm. Many cells in the periderm contain dark staining tannins. Deep to the periderm is a narrow cortex of parenchyma cells. Technical Questions:[email protected]
cross section: Syringa leaf magnification: 400x Berkshire Community College Bioscience Image Library The upper and lower epidermis are uniseriate with a thin waxy cuticle. Stomata are abundant on the lower or abaxial surface and may occasionally be seen on the upper or adaxial surface as well. Small mushroom shaped peltate trichomes are also present in the lower epidermis. These secretory trichomes have short stalks, appearing to sink into the epidermis. A large upper palisade mesophyll is composed of two layers of elongated, densely packed photosynthetic parenchyma interrupted by an occasional substomatal air spaces. A smaller lower spongy mesophyll is composed of aerenchyma; loosely arranged photosynthetic parenchyma with abundant air spaces. Technical Questions:[email protected]
cross section: Elodea stem common name water weed magnification: 100x Berkshire Community College Bioscience Image Library Submerged hydrophytes like Elodea show numerous adaptations to an aquatic life. Notably there are no internal support tissues like collenchyma or sclerenchyma. The stem is entirely support by the water. The epidermis is uniseriate and photosynthetic with a thin to non-existent cuticle and scattered stomata. The bulk of the stem is occupied by a cortex that consists of a narrow outer zone of densely packed parenchyma cells and a large inner zone of aerenchyma with large radially arranged air pockets. The cells of the entire cortex contain abundant chloroplasts. Vascular tissues are limited to the central stele and show no clear differentiation into xylem and phloem. In some specimens a single xylem vessel may be seen in the center of the stele. A large air cavity occupies the center of the stele. Technical Questions:[email protected]
cross section: Tilia Early one year stem common name: Linden or Basswood magnification: 100x Berkshire Community College Bioscience Image Library In this young stem, early in the first year of growth, the well cutinized and single layered epidermis overlays a cortex with two distinct layers; an outer cortex of tightly packed collenchyma and an inner cortex of open airy parenchyma. Within the first year of growth the underling activity of the cork cambium begins to replace the cutinized epidermis and outer cortical tissues with a protective layer of cork rich periderm. 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 cork cambium or phellogen and just beneath that layers of cork parenchyma or phelloderm. The vascular cylinder consists of an outer ring of primary phloem, a middle ring of vascular cambium and a deeper larger ring of primary xylem. Bulging into the pith are small masses of the first xylem consisting of small protoxylem cells overlaid by a few larger, heavier walled cells of metaxylem. Above this and extending to the cambium are columns of primary xylem divided by narrow rays, extending from the large parenchymatous pith to the phloem. The deepest zone of primary xylem is separated from the parenchymatous central pith by a well defined starch sheath of dark staining starch filled parenchyma cells. Many cells in the periderm, cortex and pith contain dark staining tannins. Technical Questions:[email protected]
cross section: Ficus leaf magnification: 100x Berkshire Community College Bioscience Image Library In most, but not all Ficus species, the lower epidermis is uniseriate, consisting of smaller, compactly arranged, and less heavily cutinized cells. Sunken stomata with sub-stomatal chambers are present in the lower epidermis. In some Ficus species small cystoliths are seen in the lower epidermis. The mesophyll is differentiated into upper palisade and lower spongy zones. The palisade mesophyll consists of several layers of densely packed, columnar parenchyma cells that contain abundant chloroplasts. The parenchyma cells of the spongy mesophyll have fewer chloroplasts and are loosely arranged with large intracellular air spaces. Embedded in the mesophyll are vascular bundles of varying sizes. The bundles are closed, collateral and wrapped in clear parenchymatous bundle sheaths. Xylem occurs to the upper or adaxial surface and phloem to the lower or abaxial surface. In larger vascular bundles patches of supported sclerenchyma occur above the xylem and below the phloem. Abundant dark staining lactifers produce latex like substances. Vascular bundles of the petiole and midvein are leptocentric with a ring of xylem surrounding central phloem. Technical Questions:[email protected]
cross section: Pinus stem magnification: 400x Triarch quadruple stain Berkshire Community College Bioscience Image Library During the first year of growth the cutinized epidermis is replaced by protective growth of cork rich periderm. The outer periderm consists of layers of cork cells, the phellem, which produces waterproofing suberin. Cork cells are dead at maturity. Deep to the phellem is a living layer of cork cambium or phellogen and beneath that, layers of cork parenchyma or phelloderm. Many cells in the periderm contain dark staining tannins. The cortex is divided into a thin outer hypodermis of lignified sclerenchyma cells and thicker inner cortex of thin walled parenchyma cells containing chloroplasts. Large resin ducts are surrounded by secretory parenchyma that produces resins and turpentines. Some cells enlarge into dark staining tyloses. Both endoderm and pericycle are inconspicuous. Visit the BCC Bioscience Image featuring the Microscopic World of Plants. www.berkshirecc.edu/biologyimages Technical Questions:[email protected]
radial section: Pinus stem magnification: 400x iron-alum hematoxylin and safranin stain Berkshire Community College Bioscience Image Library Gymnosperms like Pinus rely entirely on tracheids for water flow and mechanical support. True xylem vessels and wood parenchyma are lacking. While fibers are generally absent older stems may contain some fiber tracheids. The uniform wood of Gymnosperms like Pinus consists almost entirely of longitudinally oriented bands of narrow, pale staining tracheids. Emerging at right angles are narrow xylem rays, one cell thick and a few cells high, and composed of clear, thin walled parenchyma cells. The lumen of many tracheids is crossed by branched trabeculae. Tracheid side walls contain large circular bordered pits that function to move water from tracheid to tracheid while preventing air flow from embolized tracheids. The membrane of each bordered pit is marked by a pale, thin, porous outer margo and thicker, darker, inner torus. Also emerging at right angles are occasional large resin ducts, lined with living secretory parenchyma that produce resins and many toxic terpenes including turpentines. Technical Questions:[email protected]
cross section: Syringa leaf magnification: 400x Berkshire Community College Bioscience Image Library The upper and lower epidermis are uniseriate with a thin waxy cuticle. Stomata are abundant on the lower or abaxial surface and may occasionally be seen on the upper or adaxial surface as well. Small mushroom shaped peltate trichomes are also present in the lower epidermis. These secretory trichomes have short stalks, appearing to sink into the epidermis. Technical Questions:[email protected]
cross section: Pinus needle magnification: 400x Triarch quadruple stain Berkshire Community College Bioscience Image Library 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. Visit the BCC Bioscience Image featuring the Microscopic World of Plants. www.berkshirecc.edu/biologyimages Technical Questions:[email protected]
cross section: Pinus needle magnification: 400x Triarch quadruple stain Berkshire Community College Bioscience Image Library 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. Visit the BCC Bioscience Image featuring the Microscopic World of Plants. www.berkshirecc.edu/biologyimages Technical Questions:[email protected]
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