Which process is not prevented in maize?

The devices to discourage self-pollination are:

Heterostyly is a contrivance for . . . . . . .

In a bisexual flower,if androecium and gynoecium mature at different times,the phenomenon is known as a

In which of the following mechanisms is there a physical barrier between the stigma and the anther in bisexual flowers?

Self-incompatibility is a device for
$I$. Ensuring cross-pollination
$II$. Preventing self-pollination
$III$. Ensuring self-fertilisation
$IV$. Genetic control for self-fertilisation
Choose the correct statements from those given above.