root apex: During the later stages of development of embryo, the cells at the root pole become arranged in a pattern characteristic of the species. This group of cells comprises the apical meristem of the primary root. The cells of this region are all relatively undifferentiated and meristematic, densely protoplasmic and with large nuclei and they all undergo active division. The tissues of the mature root are eventually derived from a number of these cells of the apical meristem, which are termed initials. In contrast to the apical meristem of the shoot, that of the root produces cells not only toward the axis but also away from it, for it initiates the root produces cells not only toward the cap the root meristem is not terminal but sub-terminal in its position, in the sense that it is located beneath the root cap. The root apex also differs from the shoot meristem in that it forms not lateral appendages comparable to the leaves, and no branches. The root branches are usually initiated beyond the region of most active growth and they arise endogenously. It also produce no nodes and internodes, and therefore, the root grows more uniformly in length than the shoot, in which the internodes elongate much more than the nodes.
In the angiosperms there are three, rarely four, groups of initials. In the dicotyledons the distal group forms the cap and the dermatogen; the median group, the periblem; the innermost, the plerome. The most characteristic is the common origin of cap and dermatogen. In monocotyledons, there are three groups of initials which form four zones, but the outermost, independently, form the cap, and that next beneath, the dermatogen and periblem. The most characteristic of this type is that the origin and structure of the cap is independent. Moreover the two zones that are formed by one group of initials(dermatogen and periblem) are different from those(cap dermatogen) similarly formed in the dicotyledons.
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| Root Apex |
