The Leaf : Internal Structure
A leaf is composed of several distinct cell layers. The upper layer of a leaf is called the upper epidermis. Its main function is to protect the other layers of the leaf. Epidermis is classified as a protective tissue in plants. Beneath the epidermis is a layer of palisade cells. Palisade cells are long cells arranged vertically. These cells, along with the spongy layer beneath them, contain chlorophyll. Photosynthesis occurs in these cells of a leaf.
Located throughout a leaf are veins with two types of vascular tissue, xylem and phloem. Xylem cells carry water and minerals. Phloem cells carry food. The veins of the leaves connect with the veins of the stem, which are continuous with those of the roots. Through the veins, water and minerals move from roots to leaves, and food is carried from leaves to other parts of the plant.
The lower layer of a leaf is the lower epidermis. It contains guard cells. Guard cells surround and regulate the opening and closing of pores cells stomata.
แหล่งข้อมูล : BIOLOGY living systems. Page 433.
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