Which one of the following is NOT an outbreeding device to promote...

Outbreeding devices are mechanisms developed by plants to prevent self-pollination and promote cross-pollination.

Herkogamy is the presence of a physical barrier between the anther and stigma, which prevents self-pollination.

Self-sterility or self-incompatibility is a genetic mechanism that prevents self-pollen from fertilizing the ovules of the same flower.

Heteromorphy involves the production of flowers with different lengths of styles and stamens, which promotes cross-pollination.

Cleistogamy refers to the condition where flowers never open, ensuring strict self-pollination and completely preventing cross-pollination. Thus, it is an inbreeding device, not an outbreeding device.

Answer: Cleistogamy