STD-12 UNIT-6 CHA-2
REPRODUCTION IN FLOWERING PLANT
OUTBREEDING DEVICES
- Dicliny (Unisexuality).
- Flowers are unisexual so that sell pollination is not possible.
- The plants may be monoecious (bearing both male and female flowers, e.g. Maize) or dioecious (bearing male and female flowers on different plants, e.g., Mulberry. Papaya).
- Dichogamy.
- Anthers and stigmas mature at different times in a bisexual flower so as to prevent self pollination.
- (a) Protandry (Gk. protos - first, andros- male). Anthers mature earlier than stigma of the same flower. Their pollen grains become available to the stigmas of the older flowers, e.g. Sunflower, Salvia.
- (b) Protogyny (Gk. protos- first, gyne female). Stigmas mature earlier so that they get pollinated before the anthers of the same flower develop pollen grains, e.g .. Mirabilis jalapa (Four O'Clock). Gloriosa, Plantago.
- Prepotency.
- Pollen grains of another flower germinate more rapidly over the stigma than the pollen grains of the same flower, e.g. , Apple, Grape.
- Self Sterility (Self Incompatibility)
- Pollen grains of a flower do not germinate on the stigma of the same flower due to the presence of similar self sterile gene (S1 S3 in pistil and S1 or S3 in pollen grain), e.g. , Tobacco. Potato, Crucifers.
- Heterostyly.
- There are 2 or 3 types of flowers with different heights of styles and stamens.
- (a) Diheterostyly (Dimorphic Heterostyly). There are two types of flowers, pin eyed (long style and short stamens) and thrum eyed (short style and long stamens). e.g . Primula (Primrose), Jasmine.
- (b) Triheterostyly (Trimorphic Heterostyly or tristyly).
- There are three types of flowers with different heights of styles (long, medium and short and stamens (medium and short, long and short, and long and medium). Eg .. Lythrum. Pollination occurs between anthers and stigmas of the same height present in different flowers
- Herkogamy.
- It is a mechanical de vice to prevent sell pollination and promote cross pollination.
- ( a ) Extrorse dehiscence of anthers.
- ( b ) In Pansy, stigma lies inside a nap while in Kalmia the anthers occur insidecorolla pocket .
- ( c ) In Cyprepedium , stigmas lie on the route of insect entry while anthers occur near the exit .
- ( d ) In Calotropis and orchids , pollen grains occur in pollinia which can be lifted by insects only .
- ( e ) Aristolochia has foul smelling pit fall protogynous flowers where the insect gets entrapped and can come out only when the anthers mature .
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