Acetabularia is a unicellular organism, it has three parts that is cap, stem and rhizoid. they can exchange there cap even if they belongs to different species because it can modify the cap according to itself, this is controlled by nucleus so morphological character is controlled by nucleus

The correct answer is option 'D' - Acetabularia by Hammerling.

In the study of morphological differentiation, the role of the nucleus was discovered in Acetabularia by Hammerling. Acetabularia is a single-celled organism that consists of a stalk, rhizoid, and cap. Hammerling conducted experiments to investigate the role of the nucleus in determining the morphology of Acetabularia.

- Role of the Nucleus in Morphological Differentiation:

Hammerling's experiments provided evidence for the role of the nucleus in determining the morphology of Acetabularia. He conducted a series of transplantation experiments where he exchanged the caps and stalks of different species of Acetabularia.

- Transplantation Experiments:

Hammerling observed that when the cap of one species of Acetabularia was transplanted onto the stalk of another species, the resulting organism developed the morphology of the cap donor species. Similarly, when the stalk of one species was transplanted onto the cap of another species, the resulting organism developed the morphology of the stalk donor species.

- Conclusion:

These experiments led Hammerling to conclude that the nucleus plays a crucial role in determining the morphology of Acetabularia. The nucleus contains the genetic material, including the DNA, which carries the instructions for the development and differentiation of an organism. By exchanging the caps and stalks, Hammerling demonstrated that it is the nucleus that determines the morphology of Acetabularia.

- Significance of the Discovery:

Hammerling's discovery in Acetabularia provided important insights into the role of the nucleus in organismal development and differentiation. It demonstrated that the nucleus contains the genetic information necessary for determining the morphology of an organism. This finding has implications for understanding how genetic information is translated into the development of complex structures and shapes in organisms.

- Overall, Hammerling's experiments in Acetabularia revealed the role of the nucleus in morphological differentiation, highlighting the importance of genetic information in determining the form and structure of organisms.