Question

Plerome is a histogen that gives rise to
A. Pericycle
B. Pith
C. Vascular bundles
D. All of the above

Answer 1

Hint: Histogen represents the regions of the apical meristem of shoot and root. The outermost histogen produces epidermis while the cortex and endodermis are derived from the middle histogen. The innermost histogen of the shoot and root apical meristem gives rise to the stele.

Complete answer:
Based on their position in the plant body, the meristematic tissue is of three types: apical meristem, intercalary meristem, and the lateral meristem.
The apical meristem is located at the shoot and root apex. It is the growing region of shoot and root and serves as a precursor for the primary permanent tissues.
Histogen theory regarding the apical meristem was given by Hanstein. Accordingly, the shoot and root apical meristem of the flowering plants are made up of three distinct regions. These regions are called histogens. Dermatogen, periblem, and plerome are the common histogens present in both shoot and root apical meristem.
Plerome represents the inner region of the apical meristem. It consists of thin-walled cells that serve as precursors for stele including the pith. The stele represents the part of the stem and root present inside the cortex. It includes the pericycle, vascular bundle, and the pith. Some cells of plerome present away from the apex elongate to form procambium. Differentiation of procambium gives rise to vascular bundles while its undifferentiated part produces cambium.

So, the correct answer is D. All of the above.

Note: Dermatogen is the single-layered histogen that produces epidermis. The periblem is the multilayered histogen that gives rise to cortex and endodermis. An additional histogen called calyptrogen is also present in the root apical meristem.