配子体

更仔细的观察

植物的进化已经稳步下降的独立和大小配子体一代相比孢子体的一代。更原始的nonvascular植物,苔藓和苔类、配子体是主要的植物形式。它相对较大,而不是依赖于孢子体的营养。在一些物种,孢子体是双性恋;另一方面,男女是分开的。雌性配子留在配子体,由精子受精,通常从另一个配子体。结果胚胎发育成孢子体。这些小植物生长在或孢子体。然后通过减数分裂产生单倍体孢子,孢子体二倍体和这些都是分散的,成长为新孢子体。在维管植物中,然而,孢子体是形成更大的工厂。 For example, the familiar pine tree represents the diploid sporophyte generation. By meiosis, the pine eventually produces male and female gametophytes. The male gametophytes of the pine are small-they are the pollen grains released by male cones to be dispersed to female cones. The larger female gametophytes remain within the ovules of the female cones of the pine and are dependent on the surrounding sporophyte tissues for their nutrition. Each female gametophyte develops two egg cells, both of which are fertilized by a male gamete from a pollen grain. However, usually only one embryo will complete its development. This embryo is a new diploid sporophyte, housed within the developing pine seed. A pine seed thus contains three generations of the pine plant: the seed coat that arises from diploid tissue belonging to the ovule, the haploid gametophyte tissue that will serve as a food reserve for the embryo after germination, and the diploid embryo itself. In angiosperms, the female gametophyte has evolved into an even more reduced form. It consists of only the seven cells of the embryo sac.