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seed
Значение термина seed в knolik
seed - seed
seed - Product of a fertilized ovule, consisting of an embryo enclosed by protective seed coat(s) derived from the integument(s). Some seeds (castor oil, pine) are provided with food material in the form of endosperm tissue surrounding the embryo, in other (non-endospermic) seeds food material is stored in cotyledons, e.g. pea. Seed habit is culmination of an evolutionary development involving, in sequence, heterospory, reduction of a free-living female gametophyte generation dependent on water for sexual reproduction, and its retention within tissues of sporophyte by which it is protected and supplied with food. Occurred early in geological history and in more than one group of plants (present in Carboniferous in Gycadofilicales and in some fossil lycopods, as well as in present day conifers and flowering plants). Of equal importance was evolution of male gametophyte to pollen grain germinating by pollen tube, thus avoiding necessity for water in fertilization. Independence of water in sexual reproduction increased immensely the range of environments open for colonization. Biological advantages of seed habit include, further, protection and nutrition of embryonic plant during its development, provision of dispersal mechanisms, provision of food to tide over critical period of growth of embryo and its establishment as an independent plant after seed is shed.
Рядом со словом seed в knolik
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