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8.3: Shoot Development

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  • Coleus Shoot Tip

    Though it looks a bit alien, this is a section through a growing tip of a plant. In the center, where the alien’s head might be, is a region of small, densely packed cells. This is the SAM of the apical bud. On either side of the SAM, like two upraised arms, are the leaf primordia. These are the early stages of developing leaves. Through the center of these leaf primordia is a darker region of small cells. This is the procambium, which will develop into the vascular tissue. Lining the outer edge of the SAM and the youngest portions of the leaf primordia is the protoderm. As the protoderm matures into the epidermis, it produces hair-like projections called trichomes. Between the protoderm and the procambium is the ground meristem.

    On either side of the growing tip are two other darkened lumps of densely packed cells. These bud primordia will develop into axillary buds, producing either branches or flowers. Each bud primordium has its own SAM.

    Figure \(\PageIndex{1}\): Coleus shoot tip

    Observe a prepared slide of a Coleus shoot tip long section. Locate the meristems, tissues, and specialized cells. Draw what you see in the space below, label any important features.

    Flowchart of Shoot Development

    Below is a flowchart of eudicot shoot development in primary growth. There are two lines that will later lead to the secondary meristems. With this information and the filled in boxes, you should be able to determine which meristems and tissues go in the empty boxes.

    Fill in the diagram below with the following terms: cortex, epidermis, fascicular cambium, ground meristem, pith rays, procambium and primary xylem.. Choose a different color to represent meristems and tissues, then color the boxes accordingly.

    Figure \(\PageIndex{2}\): Flowchart of eudicot shoot development in primary growth

    How would this flowchart be different in a monocot? Draw a flowchart of monocot shoot development in the space below.

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