Aestivation in angiosperm is the mode of arrangement of the accessory members i.e sepals and petals or perianth with respect to one another in a flower bud.
Explore the similarities and differences between angiosperms and gymnosperms. Get examples of each type of seed-bearing plant.
The root apical meristem, or root apex, is a small region at the tip of a root in which all cells are capable of repeated division and from which all primary root tissues are derived. The shoot apical meristem and the primary meristems lie at the apex of the shoot and give rise to the primary tissues of the stem.
Overview of the major groups and phylogenetic relationships of angiosperms (flowering plants).
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cross section: Ammophilia leaf magnification: 400x Berkshire Community College Bioscience Image Library During periods of drought the leaves of the beach grass, Ammophila, temporarily curl to form a series of ridges and deep groves in the adaxial surface. The adaxial epidermis is uniseriate and lightly cutinized with large globular epidermal cells that occasionally extend into long needle like hairs. The outer and fully exposed abaxial epidermis is uniseriate and heavily cutinized. Most stomata are located half way down the walls of the V shaped adaxial grooves. When water is abundant the large white buliform cells at the base of the grooves absorb water, become turgid and unroll the leaf. A single large vascular bundle, bound by a bundle sheath and wrapped in heavy walled sclerenchyma, is located in the center of each ridge. The sclerenchyma extends from the apex to the base of each ridge to merge with the continuous ring of sclerenchyma that forms the abaxial hypodermis. The vascular bundles are collateral and closed with xylem of vessels and tracheids towards the adaxial surface and phloem of sieve tubes and companion cells towards the abaxial surface. Cambium is not present. Just deep to the epidermis, an unspecialized mesophyll of round chlorenchyma cells extends up each side of the ridge bundles and down and across the base of the grooves. Technical Questions:[email protected]
cross section: Nymphea leaf common name: Waterlily magnification: 100x Berkshire Community College Bioscience Image Library Both the upper (adaxial) and lower (abaxial) epidermis are uniseriate and contain chloroplasts. The air exposed adaxial epidermis is well cutinized and contain numerous stomata that open into large substomatal air chambers. The submerged abaxial epidermis has a very thin cuticle and lacks stomata. Dark staining slime glands are present on the abaxial surface. Deep to the upper epidermis are several layers of tightly packed palisade mesophyll, the chief photosynthetic tissue of the leaf. Most of the leaf interior is occupied by a deeper zone of spongy mesophyll with large air spaces. Large red staining branched astroscleroids are abundant throughout the mesophyll. Vascular bundles are centrally located with collaterally arranged xylem toward the adaxial surface and phloem to the abaxial surface. Particularly noticeable is an outer bundle sheath of large parenchyma cells. All vascular tissues are highly reduced except in the mid rib area where bundles with defined phloem, proto and meta xylem, and a protoxylem lacunae can be seen. Tannin rich parenchyma cells are occasionally associated with phloem of larger bundles. The mid rib area is supported towards the abaxial surface by a wide wedge of supportive collenchyma. Technical Questions:[email protected]
cross section: Syringa leaf magnification: 400x 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. Both midrib and smaller vascular bundles in the blades are collateral with large thick-walled xylem vessels towards the adaxial surface and smaller sieve tubes and companion cells of phloem towards the abaxial surface of the leaf. A largely parenchymatous ring of bundle sheath cells is present but difficult to distinguish in all but the smallest vascular bundles. Large masses of collenchyma support mid rib and larger vascular bundles towards the adaxial and abaxial surfaces, but do not extend into the blade. Technical Questions:[email protected]
cross section: Yucca leaf magnification: 400x Berkshire Community College Bioscience Image Library The leaves of Yucca show numerous structural adaptations that extend their tolerance to drought and desiccation. The epidermis is unseriate and heavily cutinized with sunken stomata evenly distributed on both adaxial and abaxial surfaces. Stomata overlay substomatal chambers and that are roofed by epidermal cells with ledge like extensions of cutin. While the mesophyll is poorly differentiated at leaf tips the body of leaf shows one or two layers of tightly packed palisade mesophyll just beneath the epidermis. The bulk of the leaf interior is occupied by spongy mesophyll with large open spaces. Idioblasts containing bundles of crystals of calcium oxalate are found in all parts of the mesophyll. Each vascular bundle is wrapped by bundle sheath cells and supported towards adaxial and abaxial surfaces by well-developed caps of supportive sclerenchyma. Abaxial sclerenchyma caps are especially well developed in the smaller peripheral vascular bundles towards the abaxial surface. 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:Zea leaf common name: corn magnification: 400x Berkshire Community College Bioscience Image Library The iso-bilateral leaf of Zea is typical of most monocots. Both upper and lower epidermis are uniseriate and well cutinized. Within the upper, or adaxial, epidermis, large white bulliform cells shrink, allowing the leaf to roll during drought. Stomata are present on both surfaces with guard cells perched above small round substomatal chambers. As with most monocots the mesophyll is unspecialized, being composed of compactly arranged somewhat round chlorenchyma cells. Numerous small and occasionally large vascular bundles are arranged in parallel series along the length of the leaf. The vascular bundles are collateral and closed with xylem of vessels and tracheids towards the adaxial surface and phloem of sieve tubes and companion cells towards the abaxial surface. Cambium is not present. Within each bundle a xylem of two oval metaxylem and a single large protoxylem cavity can be seen. Each vascular bundle is wraped by a bundle sheath of thin walled parenchyma cells. Larger bundles are supported towards both surfaces by masses of sclerenchyma that interrupt the mesophyll to form a patchy hypodermis. 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: Ligustrum leaf magnification:400x Berkshire Community College Bioscience Image Library These dicotyledonous mesophytes show structural adaptations that extend their tolerance to drought and desiccation. The uniseriate upper and lower epidermis are heavily cutinized. Stomata are almost entirely limited to the lower or abaxial surface and are enclosed within small chambers partially roofed by ledges of cutin. Numerous mushroom shaped peltate trichomes are present in the lower, and occasionally upper, epidermis. These secretory trichomes have short stalks, appearing to sink into the epidermis. The upper palisade mesophyll is composed of two compact layers of elongated photosynthetic parenchyma. A well developed lower spongy mesophyll is composed of loosely arranged photosynthetic parenchyma with abundant air spaces. The abaxial stomata open into large irregularly shaped substomatal chambers. Midrib and blade vascular bundles are collateral with large thick-walled xylem vessels towards the adaxial surface and smaller sieve tubes and companion cells of phloem towards the abaxial leaf surface. Small masses of abaxial sclerenchyma and subepidermal collenchyma are particularly well developed below the midrib vein. A largely parenchymatous ring of bundle sheath cells is visible around all vascular bundles. 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: Ligustrum leaf magnification:400x Berkshire Community College Bioscience Image Library Midrib and blade vascular bundles are collateral with large thick-walled xylem vessels towards the adaxial surface and smaller sieve tubes and companion cells of phloem towards the abaxial leaf surface. Small masses of abaxial sclerenchyma and subepidermal collenchyma are particularly well developed below the midrib vein. A largely parenchymatous ring of bundle sheath cells is visible around all vascular bundles. Technical Questions:[email protected]
Vascular tissue is organized into discrete strands called vascular bundles, each containing xylem and phloem. In woody plants, a vascular system of secondary vascular tissue develops from a lateral meristem called the vascular cambium.
cross section: Yucca leaf magnification: 100x Berkshire Community College Bioscience Image Library The leaves of Yucca show numerous structural adaptations that extend their tolerance to drought and desiccation. The epidermis is unseriate and heavily cutinized with sunken stomata evenly distributed on both adaxial and abaxial surfaces. Stomata overlay substomatal chambers and that are roofed by epidermal cells with ledge like extensions of cutin. While the mesophyll is poorly differentiated at leaf tips the body of leaf shows one or two layers of tightly packed palisade mesophyll just beneath the epidermis. The bulk of the leaf interior is occupied by spongy mesophyll with large open spaces. Idioblasts containing bundles of crystals of calcium oxalate are found in all parts of the mesophyll. The vascular bundles are arranged in parallel series across the breadth of the leaf with smaller bundles towards the periphery and larger bundles in the center of the leaf. Vascular bundles are collateral and closed with xylem of vessels and tracheids towards the adaxial surface and phloem of sieve tubes and companion cells towards the abaxial surface. Cambium is not present. Each vascular bundle is wrapped by bundle sheath cells and supported towards adaxial and abaxial surfaces by well-developed caps of supportive sclerenchyma. Abaxial sclerenchyma caps are especially well developed in the smaller peripheral vascular bundles towards the abaxial surface. Technical Questions:[email protected]
cross section: Nymphaea leaf common name: Waterlily magnification: 100x Berkshire Community College Bioscience Image Library Vascular bundles are centrally located with collaterally arranged xylem toward the adaxial surface and phloem to the abaxial surface. Particularly noticeable is an outer bundle sheath of large parenchyma cells. All vascular tissues are highly reduced except in the mid rib area where bundles with defined phloem, proto and meta xylem, and a protoxylem lacunae can be seen. Tannin rich parenchyma cells are occasionally associated with phloem of larger bundles. The mid rib area is supported towards the abaxial surface by a wide wedge of supportive collenchyma. Technical Questions:[email protected]
cross section: Potamogeton leaf magnification: 100x Berkshire Community College Bioscience Image Library Both the upper (adaxial) and lower (abaxial) epidermis are uniseriate, lightly cutinized and contain chloroplasts. The air exposed and adaxial epidermis contains numerous stomata that open into large substomatal air spaces. The submerged and abaxial epidermis lacks stomata. Deep to the upper epidermis are several layers of tightly packed palisade mesophyll, the chief photosynthetic tissue of the leaf. Most of the leaf interior is occupied by a deeper zone of spongy mesophyll, with large regularly arranged air spaces that extend throughout the leaf and into the stem. Spongy mesophyll gives the floating leaf buoyancy while providing abundant space for the storage of photosynthesis gases. Air chamber walls, termed diaphragms, consist of one or two layers of photosynthetic parenchyma with small perforations that allow easy movement of gases while blocking the movement of water. Vascular bundles are centrally located with xylem toward the adaxial surface and phloem to the abaxial surface. All vascular tissues are reduced with xylem lacking in all but the largest bundles. In smaller bundles xylem is replaced by air chambers or xylem lacuna. Phloem is better developed. All vascular tissues, including xylem, are better developed in the mid vein. Particularly noticeable is an outer bundle sheath of large parenchyma and deeper wrapping of heavy walled supportive sclerenchyma. Technical Questions:[email protected]
cross section: Yucca leaf magnification: 400x Berkshire Community College Bioscience Image Library The leaves of Yucca show numerous structural adaptations that extend their tolerance to drought and desiccation. The epidermis is unseriate and heavily cutinized with sunken stomata evenly distributed on both adaxial and abaxial surfaces. Stomata overlay substomatal chambers and that are roofed by epidermal cells with ledge like extensions of cutin. While the mesophyll is poorly differentiated at leaf tips the body of leaf shows one or two layers of tightly packed palisade mesophyll just beneath the epidermis. The bulk of the leaf interior is occupied by spongy mesophyll with large open spaces. Idioblasts containing bundles of crystals of calcium oxalate are found in all parts of the mesophyll. Technical Questions:[email protected]
