Chapter 3. Plant Tissues
Most plant cells are specialized to a greater or lesser degree, and arranged together in tissues. A plant tissue can be simple or complex depending upon whether it is composed of one or more than one type of cell. The simplest tissue found in plants is called parenchyma. The cells are not very specialized, more or less rounded or angular where packed together, and thin-walled. A type of parenchyma called chlorenchyma because the cells contain chloroplasts forms tissue (usually in the leaves) responsible for most of the photosynthesis occurring in the plant. Note that in simple tissues at least (tissues comprised mostly of one cell type), the tissue name follows from the cell type. However, tissues may also have unique anatomical names related to where in the plant they occur.
The growth of a plant requires a source of undifferentiated cells located in places where growth is needed and can be initiated to further the body plan (in comparison to animals, plants are rather open in this regard). Some enlargement in size is always possible by elongation or enlargement of existing cells, or by existing cells simply dividing. But differentiation of one cell type into another is only possible if the initial cell (mother cell) is not very specialized. Tissues comprised of cells that remain undifferentiated and supply, by their divisions, cells to form new tissues and organs, are called meristems. Meristem tissue occurs in places that allow for a very orderly pattern of growth.
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