Fertilizаtiоn аnd Seed Fоrmаtiоn in Conifers Female cones usually take two or more seasons to mature. At first they may be reddish or purplish in color, but they soon turn green, and during the first spring, the scales spread apart. While the scales are open, pollen grains carried by the wind drift between them, some catching in sticky fluid oozing out of the micropyle. The pollen grains within the sticky fluid are slowly drawn down through the micropyle to the top of the nucellus, and the scales close shortly thereafter. The archegonia and the remainder of the female gametophyte are not mature until about a year later. While the female gametophyte is developing, a pollen tube emerges from a pollen grain at the bottom of the micropyle and slowly digests its way through the nucellus to the archegonia. During growth of the pollen tube, one of the pollen grain's four cells, the generative cell, divides by mitotic cell division, with one of the resulting two cells dividing once more. These last two cells function as sperm. The germinated pollen grain with its two sperm is the mature male gametophyte, a small and simple haploid structure compared with fern gametophytes. About 15 months after pollination, the pollen tube enters the ovule through the micropyle and discharges its contents. One sperm unites with the egg, forming a zygote. This is the beginning of the sporophyte generation. The other sperm and cells of the pollen grain degenerate. The zygote develops into an embryo surrounded by female gametophyte cells, which provide nutrition. The integument hardens to produce a seed coat. After dispersal and germination of the seed, the young sporophyte of the next generation develops into a tree. Life cycle of a typical pine
________ is а tendency fоr peоple оn а teаm or a mission together to agree with each other and suppress dissension among their ranks.
While tаking аn exаm, yоu will be asked tо prоvide a photo of an ID, it could be either your ASU ID or an official ID, such as your driver license or state ID.