Evolutionary history of plants seed model is shared by basically all gymnosperms (literally: "naked seeds"), most of which encase their seeds in a woody cone or fleshy aril (the yew, for example), but none of which fully enclose their seeds. The angiosperms ("vessel seeds") are the only group to fully enclose the seed, in a carpel. Fully enclosed seeds opened up a new pathway for plants to follow: that of seed dormancy. The embryo, completely isolated from the external atmosphere and hence protected from desiccation, could survive some years of drought before germinating. Gymnosperm seeds from the Late Carboniferous have been found to contain
Economics of nuclear power plants concrete and steel, skilled workers and engineers, and safety controls by skilled inspectors. This would drive up current prices. It may be easier to rapidly expand, for example, the number of coal power plants, without this having a large effect on current prices. Existing nuclear plants generally have a somewhat limited ability to significantly vary their output in order to match changing demand (a practice called load following). However, many BWRs, some PWRs (mainly in France), and certain CANDU reactors (primarily those at Bruce Nuclear Generating Station) have various levels of load-following capabilities (sometimes substantial), which allow them to fill