Roots

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  • Corn root ls x40. Note the larger more rectangular cells in the region of elongation beyond the root cap and apical meristem.
  • Onion root tip ls x100. You can see the root cap and a portion of the apical meristem. The outer part of the root cap is shown sloughing off which it does to protect the apical meristem as the root burrows its way through the soil.
  • Fern root tip x40. Non seed plants such as ferns often have shoot and root apical meristems with a single large central apical cell.
  • Young dicot root x40 with 3 xylem lobes in the central vascular cylinder. The purple structures are starch storing leucoplasts in parenchyma cells of the root cortex.
  • Young dicot root vasuclar cylinder x100. The arrow indicates a non lignified "passage cell" in the endodermis. Such cells lack secondary cell walls and permit the passage of water and minerals between the xylem and cortex. Nearby endodermal cells that are lignified do not permit such passage.
  • Protoxylem and phloem in a young dicot root x400. You can see staining red two of the three protoxyem lobes of this root. Primary phloem (arrow) and vascular cambia are visible. The metaxylem cells in the center have not yet developed secondary cell walls and thus stain green. Later in the development of this root the metaxylem cells will form a secondary cell wall.
  • Ranunculus (Buttercup) root xs x40. There are four xylem lobes in this "typical dicot root" similar to roots illustrated in most biology textbooks. Purple staining structures are starch containing leucoplasts in cells of the cortex.
  • Ranunculus root vascular cylinder x400. In this specimen the metaxylem (central last maturing xylem) has fully formed lignified secondary cell walls. From the top center down you can see the cortex, endodermis, pericycle, phloem, vascular cambium, and xylem.
  • Psaronius root xs x40. This is a 300 million year old petrified fern root that looks very much like modern dicot roots. You can see from the outside toward the center indications of a cortex, endodermis, phloem, and 5 lobed xylem.
  • Orchid root xs x100. A two layered cortex surrounds the central vascular cylinder. The arrow indicates a passage cell in the endodermis immediately outside of a group of xylem cells.
  • Orchid root vascular cylinder x400. The arrow indicates a passage cell in the otherwise lignified endodermis. Cells with thin red staining walls inside the passage cells are xylem. Cells with thick red staining walls are fibers. There are small green staining patches of phloem with each group of fibers, alternating in position with xylem groups.
  • Monocot root xs x40. You can see a pith surrounded by a vascular cylinder, cortex, and a root hair-bearing epidermis. A branch root originates at the outer part of the vascular cylindar. The large white circular areas are tube-shaped holes in the root that function like vessels in water conduction.
  • Monocot root vascular tissue x400. Moving from the top down you can see the cortex, endodermis, 3 groups of red staining protoxylem with phloem inbetween each group, and pith. The hole in the outer pith is tube-shaped and functions like a vesses in water conduction.
  • Salix (Willow) branch root x40, pushing through the cortex of its parent root.
  • Salix branch root origin x100. You can see the "X" shaped xylem of the parent root in cross section and a longitudinal section of the branch root on the right. The branch root originates at the pericycle of the parent root, just outside the parent root's primary xylem.
  • Tulip tree woody root xs x12. This woody root with secondary xylem and phloem looks very much like a woody stem. The branch root on the left originating near the center of the parent identifies this photograph as a woody root rather than a woody stem.
  • Tulip tree root secondary tissues xs x40. From the bottom to the top you can see secondary xylem with vessels and rays, the vascular cambium, secondary phloem, and cortex.
  • Zea mays root hair x400. Root hairs are extensions of epidermal cells as seen in this root ls.
  • Clover root nodule x40. Nodules like this in legume plant roots are about the size of small peas. They contain symbiotic nitrogen fixing bacteria in their center cells. The bacteria, with the help of hemoglobin (yup, the same stuff found in animal blood) apparently made by the plant, convert atmospheric N2 gas into nitrate and nitrite ions that the plant can use.

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