Hanstein’s work revolutionized understanding of plant tissue origins in apical meristems. Question 16 asks: “Hanstein proposed -” with options: (1) Apical cell theory, (2) Histogen theory, (3) Tunica corpus theory, (4) Histogen layer theory.

Correct Answer

2. Histogen theory

Hanstein proposed the Histogen theory in 1868, stating that the apical meristem consists of three distinct tissue-forming regions (histogens): dermatogen (outermost, forms epidermis), periblem (middle, forms cortex), and plerome (innermost, forms vascular tissues and pith). This applies to both root and shoot apices, explaining organized tissue differentiation from meristematic initials.

Explanation of All Options

These theories describe shoot/root apical meristem organization, key for botany exams in molecular biology and plant development.

• Apical cell theory: Proposed by Nageli and Hofmeister, it posits a single apical initial cell divides to form all tissues; common in algae, bryophytes, and pteridophytes but not angiosperms.​

• Histogen theory: Hanstein’s model (1868) with three histogens (dermatogen → epidermis; periblem → cortex; plerome → stele); a fourth calyptrogen forms root cap. Widely taught despite limitations in shoot apices.

• Tunica corpus theory: Schmidt (1924) described shoot apices with outer tunica layers (anticlinal divisions, forms epidermis) and inner corpus (random divisions, forms ground tissues); specific to angiosperm shoots.​

• Histogen layer theory: Not a standard term; likely a distractor referring to histogen layering, but Hanstein’s is simply “Histogen theory” without “layer” modifier.​

Histogen theory remains foundational in Indian exams like CSIR NET for understanding primary growth from meristems in Kota’s botany curricula.