Answer:

Stigma determines the compatible nature of pollen.

Explanation:

The gynoecium is the female reproductive part of the flower consisting of the stigma, style, and ovary. The stigma is the uppermost part of the gynoecium, which is sticky and receptive to pollen. The style is a long slender tube-like structure that connects the stigma to the ovary. The ovary is the swollen part of the gynoecium that contains the ovules, which develop into seeds after fertilization. The synergids are the two small cells present in the embryo sac, which help in the entry of pollen tube into the ovule.

The stigma plays a crucial role in determining the compatible nature of pollen. When pollen lands on the stigma, it germinates and grows a long tube-like structure called the pollen tube, which travels down the style and enters the ovary to fertilize the ovule. However, not all pollen can germinate on every stigma. The stigma has specific molecular characteristics that determine which pollen can successfully germinate on it. This is known as stigma specificity.

The molecular basis of stigma specificity is still being studied, but it is known that there is a mutual recognition process between the stigma and the pollen. The stigma produces chemicals that attract compatible pollen, which in turn releases chemicals that help it recognize the stigma. This recognition process is necessary to ensure successful fertilization and seed production.

Therefore, the stigma plays a crucial role in determining the compatible nature of pollen, and it is the part of the gynoecium that is responsible for ensuring successful fertilization and seed production.