stigma is the name used to designate the tubular protrusion from the pollen grain.
what name is used to designate the tubular protrusion from the pollen grain?
stigma
once a pollen grain settles on a compatible pistil, it may germinate in response to a sugary fluid secreted by the mature stigma. lipids at the surface of the stigma may also stimulate pollen tube growth for compatible pollen. plants that are self-sterile often inhibit the pollen grains from their own flowers from growing pollen tubes. the presence of multiple grains of pollen has been observed to stimulate quicker pollen tube growth in some plants. the vegetative cell then produces the pollen tube, a tubular protrusion from the pollen grain, which carries the sperm cells within its cytoplasm. the sperm cells are the male gametes that will join with the egg cell and the central cell in double fertilization. the first fertilization event produces a diploid zygote and the second fertilization event produces a triploid endosperm.
pollen tube
pollen grains are usually spherical to ellipsoid in shape, sometimes triangular, about 20 to 30 micrometres along their long axis and 20 to 30 µm in diameter. they are typically monosulcate, meridionosulcate or more rarely trichotomosulcate. the sulcus is a furrow which runs along the surface of the pollen grain and is usually the site at which pollination occurs. monosulcate pollen has a single furrow that runs along the pole of the pollen grain. meridionosulcate pollen have a furrow that runs along the equator of the pollen grain. trichotomosulcate pollen, on the other hand, has three furrows. the outer layer of the pollen is covered to a greater or lesser extent with ridges, spines or warts. this "sculpting" tends to be more pronounced in species that are fly-pollinated and less pronounced in those that are pollinated by beetles or bees.
aiphanes