Question

How many histogens are present in casuarina root apex?

• A. Four
• B. One
• C. Three
• D. Two

Answer 1

The correct option is D Two

According to histogen theory, as proposed by Hanstein, the root and shoot apices have three distinct meristematic regions called as histogens. These are namely, dermatogens, periblem, and plerome. The dermatogens make uniseriate epidermis by anticlinal divisions, periblem forms cortex and plerome serve as the progenitor of stele (pericycle, vascular bundles, pith rays or medullary rays and pith). Casuarina is an exception to this theory and has two histogens due to the presence of root cap position of root apex is sub terminal. Hence the maximum growth of root takes place behind the apex.

So, the correct answer is 'Two'