Q.Differentiate between dichogamy and herkogamy, giving one example of each.

Outbreeding Devices in Flowering Plants

Continued self-pollination causes inbreeding depression, so many flowering plants have evolved outbreeding (contrivances) devices that discourage self-pollination and promote cross-pollination.

Key mechanisms include:

• Dichogamy — anthers and stigma mature at different times (protandry or protogyny), preventing self-transfer.
• Herkogamy — a physical/spatial barrier separates anther and stigma in the same flower.
• Dicliny (unisexuality) — flowers are unisexual; when male and female flowers are on the same plant (monoecious) it prevents autogamy, and when on separate plants (dioecious, e.g. papaya) it prevents both autogamy and geitonogamy.
• Self-incompatibility — a genetic mechanism that inhibits pollen germination or pollen-tube growth on the stigma of the same plant.

Distinguishing herkogamy, dichogamy, dicliny and self-incompatibility, and knowing which barrier a device removes, is frequently examined. …