<Li> In morphological dormancy, germination is prevented due to morphological characteristics of the embryo . In some species, the embryo is just a mass of cells when seeds are dispersed; it is not differentiated . Before germination can take place, both differentiation and growth of the embryo have to occur . In other species, the embryo is differentiated but not fully grown (underdeveloped) at dispersal, and embryo growth up to a species specific length is required before germination can occur . Examples of plant families where morphological dormancy occurs are Apiaceae, Cycadaceae, Liliaceae, Magnoliaceae and Ranunculaceae . </Li> <Li> Morphophysiological dormancy includes seeds with underdeveloped embryos, and also have physiological components to dormancy . These seeds, therefore, require a dormancy - breaking treatments, as well as a period of time to develop fully grown embryos . Plant families where morphophysiological dormancy occurs include Apiaceae, Aquifoliaceae, Liliaceae, Magnoliaceae, Papaveraceae and Ranunculaceae . Some plants with morphophysiological dormancy, such as Asarum or Trillium species, have multiple types of dormancy, one affects radicle (root) growth, while the other affects plumule (shoot) growth . The terms "double dormancy" and "two - year seeds" are used for species whose seeds need two years to complete germination or at least two winters and one summer . Dormancy of the radicle (seedling root) is broken during the first winter after dispersal while dormancy of the shoot bud is broken during the second winter . </Li> <Li> Physiological dormancy means the embryo, due to physiological causes, cannot generate enough power to break through the seed coat, endosperm or other covering structures . Dormancy is typically broken at cool wet, warm wet or warm dry conditions . Abscisic acid is usually the growth inhibitor in seeds, and its production can be affected by light . <Ul> <Li> Drying, in some plants, including a number of grasses and those from seasonally arid regions, is needed before they will germinate . The seeds are released, but need to have a lower moisture content before germination can begin . If the seeds remain moist after dispersal, germination can be delayed for many months or even years . Many herbaceous plants from temperate climate zones have physiological dormancy that disappears with drying of the seeds . Other species will germinate after dispersal only under very narrow temperature ranges, but as the seeds dry, they are able to germinate over a wider temperature range . </Li> </Ul> </Li> <Ul> <Li> Drying, in some plants, including a number of grasses and those from seasonally arid regions, is needed before they will germinate . The seeds are released, but need to have a lower moisture content before germination can begin . If the seeds remain moist after dispersal, germination can be delayed for many months or even years . Many herbaceous plants from temperate climate zones have physiological dormancy that disappears with drying of the seeds . Other species will germinate after dispersal only under very narrow temperature ranges, but as the seeds dry, they are able to germinate over a wider temperature range . </Li> </Ul>

What is the function of the seed in a plant