Botany and Plant Science

When a flower has both the essential whorls, i.e., androecium and gynoecium (male and female reproductive units), including stamens, carpels and an ovary, it is called as bisexual or perfect flower. In bisexual flowers, the stamens are generally numerous.
Thus, the correct answer is option D.

Self-pollination is when pollen from the same plant arrives at the stigma of a flower or at the ovule (in gymnosperms). There are two types of self-pollination. In autogamy, pollen is transferred to the stigma of the same flower. In geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm. Some plants have mechanisms that ensure autogamy, such as flowers that do not open, or stamens that move to come into contact with the stigma. 

Flowers by nature are mostly cross pollinated. There are various adaptations for this process. In unisexual and bisexual flowers, certain devices are present for the effective self pollination and avoiding cross pollination, which are called as contrivances of self pollination. They are: bisexuality- both male and female sex organs in single flower, homogamy- inbreeding and cleistogamy- propagation using non-opening, self pollinating flowers.

Very less number of seeds were seen in the flower which undergoes self-pollination.

A mechanism to prevent cross-pollination is called cleistogamy. It is a condition in which flower does not open. In such flowers, the anthers and sigma lie close to each other. When anther dehisces in the flower buds, pollen grains come in contact with stigma to effect pollination, e.g., Arachis hypogea. It ensures seed formation even in the absences of any pollination agent. It is cheaper for the plant as there is no costly nectar or fragrance which the plant has to produce for pollination.

A bisexual flower which never opens is cleistogamous. It is a condition in which flower does not open. It is an adaptation seen in plants to ensure self-pollination. In such flowers, the anthers and stigma lie close to each other. When anther dehisces in the flower buds, pollen grains come in contact with stigma to effect pollination, e.g., Arachis hypogaea. 

Cleistogamy is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers. The largest genus of cleistogamous plants is Viola.

The anthers and stigmas of chasmogamous or the open flowers are brought together by the growth, bending as well as by folding. In Catharanthus, the growth of style brings the stigma in contact of ripe anthers present on the mouth of corolla tube When cross-pollination fails in Sunflower, the bifid bent style stigma curls back so as to pick the pollen sticking to the surface of style. It is a fail-safe mechanism of self-pollination.

So the correct option is A.

Tape grass is a submerged hydrophyte. It is a dioecious plant with the flowers borne underwater. The male flowers detach on maturity and float on the surface of the water while the female flowers grow underwater and they come up to the surface with the help of their thin long stalk.

So the correct option is C.

In Salvia, pollination is entomophilous, which means it occurs by insects. Pollination occurs by the lever or turns pipe mechanism. The petals of the Salvia are bifurcated. When the insect visits some flower and sits on the petals, then the stamens are brought down to the touch the back of insect and pollen are laden on it.

When the insect visits another flower, cross-pollination occurs.

 Thus, the correct answer is A.

Continued self-pollination over many generations leads to the accumulation of recessive deleterious alleles, a phenomenon known as inbreeding depression.