megasporangium การใช้

• The megasporangium bears an unopened distal extension protruding above the multilobed integument.
• The megasporangium bears an unopened distal extension protruding above the mutlilobed integument.
• A megasporocyte inside a megasporangium or ovule undergoes meiosis, producing four megaspores.
• A megasporangium invested in protective layer called an integument is known as an ovule.
• The first seed plants, megagametophyte remains inside the megasporangium, attached to the parent plant.
• A very small slit ( micropyle ) remains, meaning that the megasporangium is still exposed to the atmosphere.
• The pollen tube elongates and pierces and grows through the megasporangium wall and delivers the sperm cells to the female gametophyte inside.
• The megagametophyte develops within the megaspore of extant seedless vascular plants and within the megasporangium in a cone or flower in seed plants.
• The vessels as found in the angiosperms, and the megasporangium is covered by three envelopes, like the ovary structure of angiosperm flowers.
• The fossil pieces of " Runcaria heinzelinii " that have been found are short branched stems that at their tips have a radially symmetrical megasporangium surrounded by a cupule.
• The " Anthophyte Theory " was based on the observation that a gymnospermic family vessels as found in the angiosperms, and the megasporangium is covered by three envelopes, like the ovary structure of angiosperm flowers.
• A Middle Devonian precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years . " Runcaria ", small and radially symmetrical, is an integumented megasporangium surrounded by a cupule.
• A middle Devonian precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years . " Runcaria ", small and radially symmetrical, is an integumented megasporangium surrounded by a cupule.
• The pollen enters a pollen chamber close to the nucellus, and there it may wait for a year before it germinates and forms a pollen tube that grows through the wall of the megasporangium ( = nucellus ) where fertilisation takes place.
• This system paved the way for ovules and seeds : taken to the extreme, the megasporangia could bear only a single megaspore tetrad, and to complete the transition to true ovules, three of the megaspores in the original tetrad could be aborted, leaving one megaspore per megasporangium.
• The pollen grains are dispersed by the wind to the female, ovulate cone that is made up of many overlapping scales ( sporophylls, and thus megasporophylls ), each protecting two ovules, each of which consists of a megasporangium ( the nucellus ) wrapped in two layers of tissue, the integument and the cupule, that were derived from highly modified branches of ancestral gymnosperms.