1. Dicliny: Dicliny or unisexuality is a condition in which the flowers are either staminate (male) or pistillate (female).

a) Monoecy

• Staminate and pistillate flowers occur in the same plant, either in the same inflorescence, e.g., Castor, mango and coconut, or in separate inflorescences, chestnut, strawberries, rubber, grapes and cassava.

b) Dioecy

• The male and female flowers are present on different plants, i.e., the plants in such species are either male or female, e.g., papaya, date, hemp, asparagus, and spinach.
• In general, the sex is governed by a single gene, e.g., asparagus and papaya. In some cases, there are hermaphrodite plants in addition to males and females, and a number of intermediate forms may also occur.

2. Stamens and pistils of hermaphrodite flowers may mature at different times facilitating cross -pollination.

a) Protogyny. In crop species like bajra, pistils mature before stamens.

b) Protandry. in crops like Maize and sugarbeets, stamens mature before pistils.

3. In Lucerne or alfalfa, stigmas are covered with a waxy film. The stigma does not become receptive until this waxy film is broken. The waxy membrane is broken by the visit of honey bees which also effect cross-pollination.

4. A combination of two or more of the above mechanisms may occur in some species. This improves the efficiency of the system in promoting cross-pollination. For example, Maize exhibits both monoecy and protandry.

5. Self-Incompatibility:

• It refers to the failure of pollen from a flower to fertilize the same flower or other flowers on the same plant.
• Self-incompatibility is of two types : sporophytic and gametophytic. In both the cases, flowers do not set seed on selfing.
• It is highly effective in preventing selfpollination.

6. Male Sterility:

• Male sterility refers to the absence of functional pollen grains in otherwise hermaphrodite flowers.
• Male sterility is of two types: genetic and Cytoplasmic. Cytoplasmic male sterility is termed Cytoplasmic-genetic when restorer genes are known.