Question

Histogen found at the tip of root apical meristem is
A. Plerome
B. Periblem
C. Calyptrogen
D. Dermatogen

Answer 1

Hint: Histogen is a derivative of promeristem, which is made up of a group of cells or primary tissue and is believed to give rise to new parts or organs of the plant. The histogen theory was given by the scientist Hanstein.

Complete answer:
Histogens are a zone of primary tissues in plants that are supposed to give rise to different plants or organs in the body of the plant. The Histogen theory was proposed by the scientist Hanstein in the year 1868. His theory stated that there are three distinct regions or histogens present in the shoot apical meristem of the plant that gives rise to the organs or tissues in the plant. These 3 histogen layers are- Periblem that gives rise to the Cortex and Epidermis, Plerome that gives rise to the Pith and Steele, and Dermatogen that gives rise to the epidermis and the epidermal tissue system. The dermatogen is the outermost layer, and the plerome is the innermost layer. This theory was later discarded since it does not talk about the tissues present in the root apical meristem. With further discoveries and theories, it was studied that- there is a fourth layer of histogen present in the root apical meristem that gives rise to the root cap. This histogen layer is called the Calyptrogen and is found at the growing tips of the roots. The root cap protects the roots from the outer atmosphere and damage. Root caps are a characteristic feature of monocots and are mostly found in grasses and other plants.

Option A: Plerome is a histogen layer found in the shoot apical meristem. Therefore, this is an incorrect option.
Option B: Periblem is a histogen layer found in the shoot apical meristem. Therefore, this is an incorrect option.
Option C: Calyptrogen is a histogen layer found in the root apical meristem that forms the root caps. Therefore, this is the correct option.
Option D: Dermatogen is a histogen layer found in the shoot apical meristem. Therefore, this is an incorrect option.

Hence, the correct answer is option (C)

Note: Near the root tip of the plants, a group of cells about 1000 in number are present in the shape of a hemisphere towards the center of the meristem. These cells face the root tip and consist of cells from the Epidermis, Cortex, and Steele. These cells divide at a slower rate, and this center is called the Quiescent center. It was discovered by the scientist Lionel.