Dormancy breaking often involves changes in membranes, initiated by dormancy-breaking signals. In some seeds physiological dormancy is indicated when scarification increases germination. Germination of the seeds involves pretreatment to remove dormancy arising from the thick pericarp. Gibberellins are involved in the natural process of breaking dormancy and other aspects of germination. Botanists can use the term "seed hibernation" to refer to a form of seed dormancy. For hibernating species, weight gain is important as it provides nourishment during winter dormancy. Typically, temperate woody perennial plants require chilling temperatures to overcome winter dormancy (rest). The endosperm of some species is responsible for seed dormancy. Not all seeds undergo a period of dormancy. ABA also prevents loss of seed dormancy. After a period of dormancy, they reactivate and produce merozoites. However, the Geysir in Iceland has had periods of activity and dormancy. However, this method is only plausible for plants with seed dormancy. During winter dormancy, the fetus attaches to the uterine wall. A dormancy and/or latency period may be entered.