| 11. | Three cells die and one that is most distant from the micropyle develops into the megaspore.
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| 12. | The plants are heterosporous with spores of two different size classes, known as megaspores and microspores.
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| 13. | Heterosporic plants, as their name suggests, bear spores of two sizes microspores and megaspores.
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| 14. | Since an individual female spore is considerably larger than a male spore, it is termed a megaspore.
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| 15. | This megaspore becomes larger and the nucleus of it undergoes mitosis three times until there are eight nuclei.
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| 16. | Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period.
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| 17. | In heterosporous organisms, two types of spores exist : microspores give rise to males and megaspores to females.
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| 18. | The transition to ovules continued with this megaspore being " boxed in " to its sporangium while it germinates.
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| 19. | As with all seed-plants, the lyginopteridalean ovules had just one functional seed megaspore within the nucellus.
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| 20. | The surviving one develops as a megaspore and divides repeatedly to form an immature female gametophyte ( egg sac ).
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