In case of polyembryony, if an embryo develops from the synergid and another from the nucellus which is haploid and which is diploid?
Embryo developed from the synergid is haploid as the ploidy of the synergid is haploid. Embryo developed from the nucellus is diploid as the ploidy of the nucellus is diploid.
Can an unfertilised, apomictic embryo sac give rise to a diploid embryo? If yes, then how?
Yes, if megaspore develops into embryo sac without meiotic division egg will be diploid. Diploid egg develops into embryo by mitotic divisions.
Which are the three cells found in a pollen grain when it is shed at the three celled stage?
In over 60\% of angiosperms, pollen grains are shed at the two cell further stage (vegetative cell and generative cell). In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed at the (three-celled stage (are vegetative cell and two male gametes).
$$ \text { What is self-incompatibility? } $$
It is a genetic mechanism which prevents self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
$$ \text { Name the type of pollination in self-incompatible plants. } $$
In self-incompatible plants, (while self-pollination is incompatible) cross-pollination is occurs.