Permanent Tissues

Once a cell produced by an apical or lateral meristem stops dividing - whether for good or only temporarily - it becomes a permanent tissue: it takes on a fixed shape, size and job. Permanent tissues split into two structurally different classes. Simple permanent tissues are built from a single, uniform cell type doing one job throughout - parenchyma, collenchyma and sclerenchyma each fall entirely into this bracket. Complex permanent tissues, by contrast, are built from several distinct cell types that only work as a functional unit together - xylem, for instance, needs its water-conducting tracheids/vessels, its supportive fibres and its living parenchyma all present at once to do its job properly, and the same is true of phloem. The practical difference between a meristematic and a permanent cell is stark and easy to summarise: meristematic cells keep dividing, stay small, undifferentiated and isodiametric, and lack intercellular spaces, vacuoles or wall thickenings, while permanent cells never divide again, are fully differentiated, vary widely in shape and size, and typically do have intercellular spaces and vacuoles. Table 9.1 in this section pulls every tissue introduced across the rest of the chapter into one place, cross-ref …