Florence (Firenze) 10 day weather forecast, updated four times a day and shows the weather summary plus detailed sun, rain, snow, wind and temperature. The weather forecast extends out to 10 days showing information for morning, afternoon and overnight.
Definition of double helix. : a helix or spiral consisting of two strands in the surface of a cylinder that coil around its axis; especially : the structural arrangement of DNA in space that consists of paired polynucleotide strands stabilized by cross-links between purine and pyrimidine bases â compare alpha-helix, watson-crick model.
double fertilization. A mechanism of fertilization in angiosperm s, in which two sperm cells unite with two cells in the embryo sac to form the zygote and endosperm. double helix ... Double fertilization gives rise to the zygote and endosperm. After landing on a receptive stigma, the pollen grain absorbs moisture and germinates, producing a pollen tube that extends down the style toward the ovary.