Question

Histogen theory is more applicable for?
a. Root Apex
b. Meristematic tissue
c. Both A and B
d. None of the above

Answer 1

Hint: The histogen theory was proposed by Hanstein (1870). The histogen theory is intricate to apply to several types of roots, and there has been indecision about the numbers of histogens. The discovery of the “quiescent center” in the root apex has clarified many features' aftermath. The quiescent center of the root tip is generally present in angiosperm and probably also in gymnosperms.

Complete answer:
The root vascular tissues are cylindrical in shape, cortex, and epidermis. The group of cells or histogens before time, within the apical meristem plerome, periblem, and dermatogen correspondingly. A fourth histogen, the calyptrogen, forms the root cap.

According to this theory, the tissues of a plant originating from a mass of meristem where the following three (histogens) can be distinguished:
- Dermatogen: It is the outermost layer of the meristem. It gives rise to the epidermis of the root and stem.
- Periblem: It is destined to form the cortex of root, shoot, and issue leaves.
- Plerome: This region gives rise to the vascular cylinder of stem and root including pith. It is the central core of the stem and root and the cells composing this zone are very irregular.

The immature mass of cells which is commonly known as meristems is the meristematic tissue. They have the power to divide cells.

Hence, the correct answer is option (A).

Note: The quiescent center of the root tip perhaps plays a role similar to that of the apical cell in some lower plant roots, maintaining the geometry of the system. It has also been suggested that it may be concerned with the production of growth hormones, even though no direct evidence exists. When roots are injured mechanically or by radiation, the cells of the center can recommence a rapid division rate, and they then contribute to regeneration.