Control of the differentiation of vascular tissues

Abstract

In animals, there are probably about 100 or more different cell types. In plants, there are fewer, probably about 40 (Table 7.1). Plant cell types are distinguished by cell wall structure, shape, size and position of the cells, and cell contents. The reactions of the cells to the common histological stains are helpful here. Lignified cell walls, for example, stain intense red with safranin. Because of their frequently larger size and characteristically thick, pitted walls, xylem elements are often the most easily recognized. Phloem cells are less easily recognized, but can be detected by stains specific for callose, which is a carbohydrate that forms on phloem sieve plates. Because they are organized into bundles or strands, vascular tissues — especially xylem and phloem — are often the most obvious tissues. Also, as their development has proved to be amenable to experimental manipulation, their differentiation has been studied much more than that of other cell types.