Soil seed bank  The soil seed bank is the natural storage of seeds, often dormant, within the soil of most ecosystems. The study of soil seed banks started in 1859 when Charles Darwin observed the emergence of seedlings using soil samples from the bottom of a lake. The first scientific paper on the subject was published in 1882 and reported on the occurrence of seeds at different soil depths. Weed seed banks have been studied intensely in agricultural science because of their important economic impacts; other fields interested in soil seed banks include forest regeneration and restoration ecology. Many taxa have been classified according to the longevity of their seeds in the soil seed bank. Seeds of "transient" species remain viable in the soil seed bank only to the next opportunity to germinate, while seeds of "persistent" species can survive longer than the next opportunity—often much longer than one year. Species with seeds that remain viable in the soil longer than five years form the "long-term" persistent seed bank, while species whose seeds generally germinate or die within one to five years are called "short-term" persistent. A typical long-term persistent species is "Chenopodium album" (Lambsquarters); its seeds commonly remain viable in the soil for up to 40 years and in rare situations perhaps as long as 1,600 years. A species forming no soil seed bank at all (except the dry season between ripening and the first autumnal rains) is "Agrostemma githago" (Corncockle), which was formerly a widespread cereal weed. Longevity of seeds is very variable and depends on many factors; few species exceed 100 years. In typical soils the longevity of seeds can range from nearly zero (germinating immediately when reaching the soil or even before) to several hundred years. Some of the oldest still-viable seeds were those of Lotus ("Nelumbo nucifera") found buried in the soil of a pond; these seeds were estimated by carbon dating to be around 1,200 years old. One of the longest-running soil seed viability trials was started in Michigan in 1879 by James Beal. The experiment involved the burying of 20 bottles holding 50 seeds from 21 species. Every five years, a bottle from every species was retrieved and germinated on a tray of sterilized soil which was kept in a growth chamber. Later, after responsibility for managing the experiment was delegated to caretakers, the period between retrievals became longer. In 1980, more than 100 years after the trial was started, seeds of only three species were observed to germinate: moth mullein ("Verbascum blattaria"), common mullein ("Verbascum thapsus") and common mallow ("Malva neglecta").