Most of the tissues we have discussed thus far consist of one kind of cell, but a few important tissues are always composed of two or more kinds of cells and are sometimes referred to as complex tissues. Two of the most important complex tissues in plants, xylem and phloem, function primarily in the transport of water, ions, and soluble food (sugars) throughout the plant. Some complex tissues are produced by apical meristems, but most complex tissues in woody plants are produced by the vascular cambium and are often referred to as vascular tissues.
The epidermis, which forms a protective layer covering all plant organs, consists primarily of parenchyma or parenchyma-like cells, but it also often includes specialized cells involved in the movement of water and gases in and out of plants, secretory glands, various hairs, cells in which crystals are isolated, and others that greatly increase absorptive parts of roots. Accordingly, the epidermis and tissues with secretory cells are discussed in this section.
Periderm, which comprises the outer bark of woody plants, consists mostly of cork cells, but it is included in this discussion because it contains pockets of parenchyma-like cells.
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Xylem
Phloem
Epidermis
Periderm
Secretory Cells and Tissues
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