Question

Write explanatory notes on the following: (i) Water pollination (ii) Polyembryony.

Hint:

Water pollination: pollen carried by water currents, as in Vallisneria. Polyembryony: more than one embryo in a single seed, common in citrus.

Answer 1

Water pollination:
Water pollination, or hydrophily, is pollination carried out with water as the transferring agent, and it is uncommon, seen in only a small number of fully or partly submerged aquatic plants.
In genera like Vallisneria, the plant is unisexual: male flowers detach from the parent plant and float freely on the water surface, while female flowers stay attached but rise to the surface on a long stalk.
Water currents carry the floating male flowers to the female flowers, allowing pollen to reach the stigma, after which the female flower is pulled back under water as the fruit develops.
In fully submerged plants such as Zostera, pollen grains are long and thread like and are released directly into the water, drifting until they reach the stigma of a female flower underwater.

Polyembryony:
Polyembryony is the occurrence of more than one embryo developing within a single seed, instead of just one.
It commonly happens because extra embryos form from nucellar or integument cells surrounding the embryo sac, a phenomenon especially common in citrus fruits, or because more than one egg cell or synergid gets fertilised in the same embryo sac.
This is agriculturally valuable, because nucellar embryos are genetically identical to the mother plant, so growers use polyembryony in citrus species to raise disease-free, true-to-type seedlings without depending on grafting.