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polyembryony presence of more than one embryo in a seed is termed polyembryony the phenomenon first discovered in orange seeds by leeuwenhoek 1719
mature embryoa typical dicotyledonous embryo as seen in a median longitudinal section consists of an embryonal axis having two broad cotyledons the
monocotyledonous embryo the early development of the proembryo in monocots follows the same pattern as in the dicots however at the time of
histogenesis and organogenesisafter the octant stage numerous cell divisions occur in various planes the proembryo become globular or bulb-shaped as
types of embryogeny on the basis of the plane of division of the zygote and of the cells of the 2-celled proembryo and also taking into account the
zygote - embryogenesisthe fertilized egg or zygote is situated at the micropylar endpole of the embryo sac its basal micropylar end is attached to
structure and fate of endosperm the cells of endosperm are usually thin-walled large isodiametric and devoid of pits and store large amount of food
morphological nature of endosperm the morphological nature of endosperm in angiosperms has been a subject of much discussion in evolution the
cytology of endosperm normally the young endosperm is triploid as it is formed by the fusion of three haploid nuclei male gamete upper polar nucleus
functions of endosperm the tissue of young endosperm is rich in food materials and various growth hormones it regulates the precise mode of embryo
mosaic endosperm - variants of endospermin some plants patches of two different colors appear in the tissues of the endosperm providing a mosaic
ruminate endosperm - variants of endospermin certain plants the surface of the mature cellular endosperm shows a high degree of irregularity and
composite endosperm - variants of endospermin the family loranthaceae the development of endosperm is unique the ovary lacks ovules the sporogenous
endosperm with micropylar and chalazal haustoria some plants develop haustoria from both micropylar and chalazal ends of endosperm in nemophila
endosperm with chalazal haustorium in grevillea robusta a member of proteaceae the endosperm is of the free nuclear type the upper part of endosperm
helobial type - endospermthis type of endosperm is intermediate between the nuclear and the cellular types the division of the primary endosperm
nuclear type - endosperm the primary endosperm nucleus divides the cell wall is not laid these nuclei and their division products form a large number
development of endospermin a fertilized embryo sac the primary endosperm nucleus is generally observed below the zygote it divides and further
significance of apomixis apomixis offers the possibility of indefinite multiplication of especially favorable biotypes without any variation due to
parthenogenesis the diploid egg produced in the embryo sacs during diplospory and apospory develops into an embryo without fertilization thus
causes of apomixis apomictic species are generally hybrids or polyploids as a consequence there is irregular meiosis apomixis appears to be
non-recurrent type as mentioned earlier it refers to embryo development in reduced embryo sacs the mechanisms identified for such cases are reduced
organization in non-reduced embryo sacs the fate of a nucleus in the embryo sac depends upon its position many irregularities in the disposition of
gonial apospory and somatic aposporygonial aposporythere is no meiosis the megaspore mother cell enlarges a small vacuole appears above and below the
recurrent type in this type euspory seen in normal cases is replaced by aneuspory diplospory because of irregular meiosis when the spore mother ceil