| 单词 | megaspore |
| 例句 | Therefore, they generate microspores, which will generate pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes. Fundamentals of Biology 2015-01-01T00:00:00Z The male spores are called microspores because of their smaller size; the comparatively larger megaspores will develop into the female gametophyte. Concepts of Biology 2013-04-25T00:00:00Z Other fossilized finds include a pinecone-like structure with megaspores and some fossilized tree trunks used to estimate the height of the trees, Wang noted. 419 million-year-old fossilized forest discovered in China 2019-08-09T04:00:00Z The megaspore 763 is filled with tissue as in typical Gymnosperms, and from some of the superficial cells 3 to 5 archegonia are developed, characterized by long multicellular necks. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 7 "Gyantse" to "Hallel" 2011-12-26T03:00:11.613Z For an account of the further development of the megaspore, and the formation of the egg-cell, from which after fertilization is formed the embryo, see Gymnosperms and Angiosperms. Encyclopaedia Britannica, 11th Edition, Volume 10, Slice 5 "Fleury, Claude" to "Foraker" 2011-04-03T02:00:20.883Z Through meiosis, the microsporangium forms microspores, and the megasporangium forms megaspores. Fundamentals of Biology 2015-01-01T00:00:00Z Like all gymnosperms, pines are heterosporous and produce male microspores and female megaspores. Concepts of Biology 2013-04-25T00:00:00Z In both forms cysts containing megaspores and megasporozoites, and others containing microspores and microsporozoites are found, considered as representing sexual differentiation thrown back to the very earliest stages of the life-cycle. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 5 "Clervaux" to "Cockade" The tissue at the apex of the megaspore grows slightly above the level of the archegonia, so that the latter come to lie in a shallow depression. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 7 "Gyantse" to "Hallel" 2011-12-26T03:00:11.613Z The behaviour of the chromosomes in meiosis or reduction division both in the pollen mother-cells and in the megaspore mother-cells which give rise to the so-called embryo-sac are fully described by Gates. Hormones and Heredity Both microspores and megaspores undergo mitosis, forming the microgametophyte and megagametophyte, respectively. Fundamentals of Biology 2015-01-01T00:00:00Z The megaspores and the female gametophytes are produced and protected by the thick tissues of the carpel. Concepts of Biology 2013-04-25T00:00:00Z Only the large megaspore survives; it produces the female gametophyte, referred to as the embryo sac. Fundamentals of Biology 2015-01-01T00:00:00Z Each megaspore may contain 2 to 6 archegonia. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 7 "Gyantse" to "Hallel" 2011-12-26T03:00:11.613Z A megaspore develops into a female gametophyte containing a haploid egg. Fundamentals of Biology 2015-01-01T00:00:00Z When the pollen lands on a female scale, a pollen tube grows toward the female gametophyte, which consists of an ovule containing the megaspore. Fundamentals of Biology 2015-01-01T00:00:00Z The male spores are called microspores, because of their smaller size, and develop into the male gametophyte; the comparatively larger megaspores develop into the female gametophyte. Fundamentals of Biology 2015-01-01T00:00:00Z When the pollen lands on a female scale, a pollen tube grows toward the female gametophyte, which consists of an ovule containing the megaspore. Fundamentals of Biology 2015-01-01T00:00:00Z The megasporangium contains megaspore mother cells, which divide by meiosis to produce haploid megaspores. Fundamentals of Biology 2015-01-01T00:00:00Z The female gametophyte is formed from mitotic divisions of the megaspore, forming an eight-nuclei ovule sac. Fundamentals of Biology 2015-01-01T00:00:00Z One of the megaspores divides to form the multicellular female gametophyte, while the others divide to form the rest of the structure. Fundamentals of Biology 2015-01-01T00:00:00Z In the female cone, megaspore mother cells are present in the megasporangium. Fundamentals of Biology 2015-01-01T00:00:00Z The megaspore mother cell divides by meiosis to produce four haploid megaspores. Fundamentals of Biology 2015-01-01T00:00:00Z The megaspore mother cell is at the center. Fundamentals of Biology 2015-01-01T00:00:00Z First, in the process of megasporogenesis, a single cell in the diploid megasporangium—an area of tissue in the ovules—undergoes meiosis to produce four megaspores, only one of which survives. Fundamentals of Biology 2015-01-01T00:00:00Z Like all gymnosperms, pines are heterosporous and generate two different types of spores: male microspores and female megaspores. Fundamentals of Biology 2015-01-01T00:00:00Z |
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