Name the part of gynoecium that determines the compatible nature of pollen grain.

Explanation

The pistil has the ability to recognise, the pollen , whether it is of the right type (compatilble) or of the wrong type (incompatible). If it is of the right type , the pistil accepts the pollen and promotes post-pollination events that lead to fertilisation . If the pollen is of wrong type, the pistil rejects the pollen.
The ability of the pistil to recognise the pollen is followed by its acceptance or rejection . It is the result of a continuous dialogue between pollen grain and the pistil mediated by chemical components of the pollen interacting with those of the pistils.