Lab 5 - PLB 105 Lab ManualFall 2009 page 5-1 Laboratory 5...

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PLB 105 Lab Manual—Fall 2009 page 5-1 Laboratory 5 Epidermis The dermal tissue system is composed of two tissues, the epidermis and the periderm. The epidermis is derived from primary meristematic tissue, the protoderm. The periderm is derived from the cork cambium, or phellogen, which is a secondary meristem. Because both tissues have the same major functions—such as gas exchange, prevention of water loss, protection against pathogen entry—and occupy the same position on the plant body, they are both in the same tissue system. The epidermis will be studied in this laboratory; periderm will be examined later when we examine root and stem secondary growth. Epidermal cells comprise the outer covering of the entire primary plant body with the exception of the tip of the shoot apex and the root cap. The function of the epidermis includes prevention of water loss, regulation of gas exchange, mechanical protection and protection from pathogens and insects, and occasionally photosynthesis or storage. Epidermal cells are variable in shape, and their exposed walls are commonly covered with a cuticle of waxes and cutin. A. Stomatal Complex Types Stomata occur among the epidermal cells in many aerial plant organs. A stoma consists of a pore surrounded by two guard cells. Stomata, together with associated subsidiary cells, form the stomatal apparatus or complex. A stoma is a controllable opening in the plant's surface that allows for gas exchange—specifically, the uptake of CO 2 . Also, when the pore is open, water vapor escapes from the plant. Stomata are commonly present in leaves and often on stems as well. Specific terminology is associated with leaf stomatal
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