Class 12 Biology Reproduction Sexual Reproduction in Flowering Plants



Rarely in angiosperms, the pollen tube develops further in embryo sac. The abnormality is called as
(a)
Metaxenia
(b)
Nemec phenomenon
(c)
Xenia
(d)
Mesogamy
Correct answer: (b) 
Solution: In Hyacinthus, Nemec observed 8 nucleated embryo sac type organisation in pollen grain. This is called as Nemec phenomenon.
Rarely in angiosperms, the pollen tube develops further in embryo sac. The abnormality is called as Nemec phenomenon.
Nemec phenomenon possessing pollen sacs have also been reported by Stow. The microspore here increases in size to form a sac like structure. The nucleus undergoes three mitotic divisions to form 8 nuclei. Of these, 3 lie at the end where exine is still intact, 3 at the opposite end and 2 in the middle. Stow observed that when the pollen embryo sacs were placed on an agar medium, together with some normal pollen grains of another variety, the pollen tubes from the latter coiled surround the pollen embryo sacs. 
Thus, the correct answer is option B.

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Similar topics
sexual reproduction in flowering plants
reproduction in organisms
evolution
human reproduction
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sexual reproduction in flowering plants
reproduction in organisms
evolution
human reproduction
reproductive health