Question

Histogen theory was proposed by
(a)Bailey
(b)Haberlandt
(c)Hanstein
(d)Schmidt

Answer 1

Hint: A German botanist who was a resident of Potsdam suggested the theory of Histogen. It was in the year 1822 that he was born. He is remembered for plant anatomy and morphology studies. He developed the 'histogen theory' in 1868 to clarify shoot apex behavior in plants.

Complete answer:
According to Hanstein's 1868 histogen theory, the shoot apical meristems found at the shoot tip in plants are derived from the apical meristematic tissues.
According to Hanstein, the three major root tissues, vascular cylinder, cortex, and epidermis, derive in the apical meristem plerome, periblem, and dermatogen, respectively, from three classes of initial cells or histogens. The calyptrogen produces the root cap, a fourth histogen.
The three layers that are distinct are:
-Dermatogen is the main meristem that forms the epidermis of the outermost layer of a plant or part of a plant.
-Periblem is a cortex forming the primary meristem. It is located between plerome and dermatogen.
-Plerome is the primary meristem that forms the main center of the plant and gives rise to stele. Procambium is the portion of pleroma from which vascular tissues are created.
So, the correct answer is, option (c) ‘Hanstein’.

Note: Dermatogen, periblem, and pleroma derive from separate initials of the apical meristem, according to Hanstein.
Further investigations reveal that, for the following two reasons, there is no general application of the subdivisions dermatogen, periblem, and plerome.
-There is no strong distinction between periblem and plerome in gymnosperm and angiosperm.
-The functions of the three histogens can not be shown.