ABSTRACT
Plant organs such as stems, roots and leaves are made up of tissues that is, collections of cells carrying out specific functions. These may be simple tissues composed of one cell type only, such as the parenchyma tissue of the stem cortex which is made up of parenchyma cells. Tissues may also be complex, containing several different types of cell. Xylem tissue, for example, contains xylem vessels, tracheids, parenchyma and sclerenchyma cells to carry out its complex function. In stems, for example, cells at the apex divide frequently to produce four kinds of tissue. The first, at the very tip, continue as meristem cells. The second (protoderm), near the outside, develops into the epidermis. The third (procambium) becomes the vascular tissues, xylem and phloem. The fourth (ground meristem) gives rise to the parenchyma, collenchyma and sclerenchyma tissues of the cortex and pith. In some plant families, intercalary meristems give rise to primary growth.
