Seed bank

Last updated
Seedbank at the USDA Western Regional Plant Introduction Station Seedbank.jpg
Seedbank at the USDA Western Regional Plant Introduction Station

A seed bank (also seed banks or seeds bank) stores seeds to preserve genetic diversity; hence it is a type of gene bank. [1] There are many reasons to store seeds. One is to preserve the genes that plant breeders need to increase yield, disease resistance, drought tolerance, nutritional quality, taste, etc. of crops. Another is to forestall loss of genetic diversity in rare or imperiled plant species in an effort to conserve biodiversity ex situ. Many plants that were used centuries ago by humans are used less frequently now; seed banks offer a way to preserve that historical and cultural value. Collections of seeds stored at constant low temperature and low moisture are guarded against loss of genetic resources that are otherwise maintained in situ or in field collections.[ citation needed ] These alternative "living" collections can be damaged by natural disasters, outbreaks of disease, or war. Seed banks are considered seed libraries, containing valuable information about evolved strategies to combat plant stress, and can be used to create genetically modified versions of existing seeds. The work of seed banks often span decades and even centuries. Most seed banks are publicly funded and seeds are usually available for research that benefits the public.[ citation needed ]

Contents

Storage conditions and regeneration

Seeds are living plants and keeping them viable over the long term requires adjusting storage moisture and temperature appropriately. As they mature on the mother plant, many seeds attain an innate ability to survive drying. Survival of these so-called 'orthodox' seeds can be extended by dry, low temperature storage. The level of dryness and coldness depends mostly on the longevity that is required and the investment in infrastructure that is affordable. Practical guidelines from a US scientist in the 1950s and 1960s, James Harrington, are known as 'Thumb Rules'. The 'Hundreds Rule' guides that the sum of relative humidity and temperature (in Fahrenheit) should be less than 100 for the sample to survive five years. Another rule is that reduction of water content by 1% or temperature by 10 °F (5.6 °C) will double the seed life span. Research from the 1990s showed that there is a limit to the beneficial effect of drying or cooling, so it must not be overdone.[ citation needed ]

Understanding the effect of water content and temperature on seed longevity, the Food and Agriculture division of the United Nations and a consultancy group called Bioversity International developed a set of standards for international seed banks [2] to preserve seed longevity. The document advocates drying seeds to about 20% relative humidity, sealing seeds in high quality moisture-proof containers, and storing seeds at −20 °C (−4 °F). These conditions are frequently referred to as 'conventional' storage protocols. Seeds from our most important species – corn, wheat, rice, soybean, pea, tomato, broccoli, melon, sunflower, etc. – can be stored in this way. However, there are many species that produce seeds that do not survive the drying or low temperature of conventional storage protocols. These species must be stored cryogenically. Seeds of citrus fruits, coffee, avocado, cocoa, coconut, papaya, oak, walnut and willow are a few examples of species that should be preserved cryogenically.[ citation needed ]

Like everything, seeds eventually degrade with time. It is hard to predict when seeds lose viability and so most reputable seed banks monitor germination potential during storage. [3] When seed germination percentage decreases below a prescribed amount, the seeds need to be replanted and fresh seeds collected for another round of long-term storage. [4]

Seeds banks may operate in much more primitive conditions if the aim is only to maintain year-by-year seed supplies and lower costs for farmers in a particular area. [5]

Challenges

One of the greatest challenges for seed banks is selection. Collections must be relevant and that means they must provide useful genetic diversity that is accessible to the public. Collections must also be efficient and that means they mustn't duplicate materials already in collections.[ citation needed ]

Keeping seeds alive for hundreds of years is the next biggest challenge. Orthodox seeds are amenable to 'conventional' storage protocols but there are many seed types that must be stored using nonconventional methods. Technology for these methods is rapidly advancing; local institutional infrastructure may be lacking.[ citation needed ]

Some seeds cannot be kept alive in storage and must be regenerated – planted to produce a new quantity of seeds to be stored for another length of time. [6] [7] Parzies et al. 2000 found that this reduced the effective population size and alleles were lost. [6] [7] Parzies' finding has since been taken seriously by banks around the world and has sparked further verification – regeneration is widely recognized to not preserve diversity perfectly. [6] [7]

Alternatives

In-situ conservation of seed-producing plant species is another conservation strategy. In-situ conservation involves the creation of National Parks, National Forests, and National Wildlife Refuges as a way of preserving the natural habitat of the targeted seed-producing organisms. In-situ conservation of agricultural resources is performed on-farm. This also allows the plants to continue to evolve with their environment through natural selection.[ citation needed ]

An arboretum stores trees by planting them at a protected site.[ citation needed ]

A less expensive, community-supported seed library can save local genetic material. [8]

The phenomenon of seeds remaining dormant within the soil is well known and documented (Hills and Morris 1992). [9] Detailed information on the role of such "soil seed banks" in northern Ontario, however, is extremely limited, and research is required to determine the species and abundance of seeds in the soil across a range of forest types, as well as to determine the function of the seed bank in post-disturbance vegetation dynamics. Comparison tables of seed density and diversity are presented for the boreal and deciduous forest types and the research that has been conducted is discussed. This review includes detailed discussions of: (1) seed bank dynamics, (2) physiology of seeds in a seed bank, (3) boreal and deciduous forest seed banks, (4) seed bank dynamics and succession, and (5) recommendations for initiating a seed bank study in northern Ontario.[ citation needed ]

Longevity

Seeds may be viable for hundreds and even thousands of years. The oldest carbon-14-dated seed that has grown into a viable plant was a Judean date palm seed about 2,000 years old, recovered from excavations at the palace of Herod the Great in Israel. [10]

In February 2012, Russian scientists announced they had regenerated a narrow leaf campion ( Silene stenophylla ) from a 32,000-year-old seed. The seed was found in a burrow 124 feet (38 m) under Siberian permafrost along with 800,000 other seeds. Seed tissue was grown in test tubes until it could be transplanted to soil. This exemplifies the long-term viability of DNA under proper conditions. [11]

Climate change

Conservation efforts such as seed banks are expected to play a greater role as climate change progresses. [12] Seed banks offer communities a source of climate-resilient seeds to withstand changing local climates. [13] As challenges arise from climate change, community based seed banks can improve access to a diverse selection of locally adapted crops while also enhancing indigenous understandings of plant management such as seed selection, treatment, storage, and distribution. [14]

Facilities

Plant tissue cultures being grown at a USDA seed bank, the National Center for Genetic Resources Preservation Plant tissue cultures, National Center for Genetic Resources Preservation, USDA.jpg
Plant tissue cultures being grown at a USDA seed bank, the National Center for Genetic Resources Preservation

There are about 6 million accessions, or samples of a particular population, stored as seeds in about 1,300 genebanks throughout the world as of 2006. [15] This amount represents a small fraction of the world's biodiversity, and many regions of the world have not been fully explored.

Seed banks classification

Seed banks can be classified in three main profiles: assitentialist, productivist or preservationist. n practice, many seed banks have a combination of these three main types, and they may have different priorities depending on the context and goals of the seed bank. [29]

  1. Assistentialist seed banks: These seed banks primarily aim to support the needs of local communities and small-scale farmers. They focus on providing seed samples that are well-suited to local conditions and are easy to grow and maintain. They prioritize seed samples that have high yield potential, are pest and disease resistant, and can be grown with minimal inputs.
  2. Productivist seed banks: These seed banks primarily aim to support large-scale agricultural production and commercial farming. They focus on providing seed samples that have high yield potential, are pest and disease resistant, and can be grown with minimal inputs. They prioritize seed samples that are well-suited to large-scale mechanized farming and can be grown in large quantities.
  3. Preservationist seed banks: These seed banks primarily aim to conserve the genetic diversity of wild and domesticated plant species. They focus on preserving the genetic diversity of plant species, and make seed samples available for research and breeding programs. They prioritize seed samples that are rare, endangered, or have unique genetic characteristics.
Seed banks classification by profile
ProfileAssitentialistProductivistPreservationist
ObjectiveConserve varieties of seeds in case they need to be used in coming harvestsConserve varieties of seeds to contribute to the improvement of current crops by crossing them with those seedsPreserve varieties of seeds in case they are destroyed by either man or natural events.
FunctioningThe bank provides seeds to farmers who lack themThe bank makes its seeds available to produce new crops of agricultural interest from these seedsThe bank does not offer its seeds but it safeguards them

Early concepts

In Zoroastrian mythology, Ahura Mazda instructed Yima, a legendary king of ancient Persia, to build an underground structure called a Vara to store two seeds from every kind of plant in the known world. The seeds had to come from plant specimens that were free of defects, and the structure itself had to withstand a 300-year apocalyptic winter. [30] Some scholars have suggested that the Norse equivalent of this myth is the underground garden Odainsaker, which was intended to withstand the three-year fimbul winter preceding Ragnarok, to protect the people (and seemingly the plants) that would repopulate the world after this event. [31]

See also

Related Research Articles

<i>Ex situ</i> conservation Preservation of plants or animals outside their natural habitats

Ex situ conservation is the process of protecting an endangered species, variety or breed, of plant or animal outside its natural habitat. For example, by removing part of the population from a threatened habitat and placing it in a new location, an artificial environment which is similar to the natural habitat of the respective animal and within the care of humans, such as a zoological park or wildlife sanctuary. The degree to which humans control or modify the natural dynamics of the managed population varies widely, and this may include alteration of living environments, reproductive patterns, access to resources, and protection from predation and mortality.

<span class="mw-page-title-main">Agricultural biodiversity</span> Agricultural concept

Agricultural biodiversity or agrobiodiversity is a subset of general biodiversity pertaining to agriculture. It can be defined as "the variety and variability of animals, plants and micro-organisms at the genetic, species and ecosystem levels that sustain the ecosystem structures, functions and processes in and around production systems, and that provide food and non-food agricultural products.” It is managed by farmers, pastoralists, fishers and forest dwellers, agrobiodiversity provides stability, adaptability and resilience and constitutes a key element of the livelihood strategies of rural communities throughout the world. Agrobiodiversity is central to sustainable food systems and sustainable diets. The use of agricultural biodiversity can contribute to food security, nutrition security, and livelihood security, and it is critical for climate adaptation and climate mitigation.

<span class="mw-page-title-main">Germplasm</span> Genetic material of an organism

Germplasm refers to genetic resources such as seeds, tissues, and DNA sequences that are maintained for the purpose of animal and plant breeding, conservation efforts, agriculture, and other research uses. These resources may take the form of seed collections stored in seed banks, trees growing in nurseries, animal breeding lines maintained in animal breeding programs or gene banks. Germplasm collections can range from collections of wild species to elite, domesticated breeding lines that have undergone extensive human selection. Germplasm collection is important for the maintenance of biological diversity, food security, and conservation efforts.

<span class="mw-page-title-main">Svalbard Global Seed Vault</span> Globally accessible seed bank on Spitsbergen, Svalbard, Norway

The Svalbard Global Seed Vault is a secure backup facility for the world's crop diversity on the Norwegian island of Spitsbergen in the remote Arctic Svalbard archipelago. The Seed Vault provides long-term storage of duplicates of seeds conserved in genebanks around the world. This provides security of the world's food supply against the loss of seeds in genebanks due to mismanagement, accident, equipment failures, funding cuts, war, sabotage, disease and natural disasters. The Seed Vault is managed under terms spelled out in a tripartite agreement among the Norwegian government, the Crop Trust, and the Nordic Genetic Resource Center (NordGen).

<span class="mw-page-title-main">Gene bank</span> Facility that preserves genetic material

Gene banks are a type of biorepository that preserves genetic material. For plants, this is done by in vitro storage, freezing cuttings from the plant, or stocking the seeds. For animals, this is done by the freezing of sperm and eggs in zoological freezers until further need. With corals, fragments are taken and stored in water tanks under controlled conditions. Genetic material in a 'gene bank' is preserved in a variety of ways, such as freezing at -196 °C in liquid nitrogen, being placed in artificial ecosystems, or put in controlled nutrient media.

<span class="mw-page-title-main">Crop Trust</span>

The Crop Trust, officially known as the Global Crop Diversity Trust, is an international nonprofit organization with a secretariat in Bonn, Germany. Its mission is to conserve and make available the world's crop diversity for food security.

Seed Savers Exchange, or SSE, is a non-profit organization based near Decorah, Iowa, that preserves heirloom plant varieties through regeneration, distribution and seed exchange. It is one of the largest nongovernmental seedbanks in the United States. The mission of SSE is to preserve the world’s diverse but endangered garden heritage for future generations by building a network of people committed to collecting, conserving, and sharing heirloom seeds and plants, and educating people about the value of genetic and cultural diversity. Since 1975, Seed Savers has produced an annual yearbook of members’ seed offerings, as well as multiple editions of The Garden Seed Inventory, and The Fruit, Nut and Berry Inventory. SSE also publishes Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners. The nonprofit has sold seeds to about 600 retail stores in the United States and Canada.

<span class="mw-page-title-main">Cary Fowler</span> American agriculturalist

Morgan Carrington "Cary" Fowler Jr. is an American agriculturalist and the former executive director of the Crop Trust, currently serving as U.S. Special Envoy for Global Food Security.

<span class="mw-page-title-main">Millennium Seed Bank Partnership</span>

The Millennium Seed Bank Partnership, formerly known as the Millennium Seed Bank Project, is the largest ex situ plant conservation programme in the world coordinated by the Royal Botanic Gardens, Kew. After being awarded a Millennium Commission grant in 1995, the project commenced in 1996, and is now housed in the Wellcome Trust Millennium Building situated in the grounds of Wakehurst Place, West Sussex. Its purpose is to provide an "insurance policy" against the extinction of plants in the wild by storing seeds for future use. The storage facilities consist of large underground frozen vaults preserving the world's largest wild-plant seedbank or collection of seeds from wild species. The project had been started by Dr Peter Thompson and run by Paul Smith after the departure of Roger Smith. Roger Smith was awarded the OBE in 2000 in the Queen's New Year Honours for services to the Project.

<span class="mw-page-title-main">Crop wild relative</span> Wild plant closely related to a domesticated plant

A crop wild relative (CWR) is a wild plant closely related to a domesticated plant. It may be a wild ancestor of the domesticated (cultivated) plant or another closely related taxon.

Crop diversity or crop biodiversity is the variety and variability of crops, plants used in agriculture, including their genetic and phenotypic characteristics. It is a subset of a specific element of agricultural biodiversity. Over the past 50 years, there has been a major decline in two components of crop diversity; genetic diversity within each crop and the number of species commonly grown.

Forest genetic resources or foresttree genetic resources are genetic resources of forest shrub and tree species. Forest genetic resources are essential for forest-depending communities who rely for a substantial part of their livelihoods on timber and non-timber forest products for food security, domestic use and income generation. These resources are also the basis for large-scale wood production in planted forests to satisfy the worldwide need for timber and paper. Genetic resources of several important timber, fruit and other non-timber tree species are conserved ex situ in genebanks or maintained in field collections. Nevertheless, in situ conservation in forests and on farms is in the case of most tree species the most important measure to protect their genetic resources.

The U.S. National Plant Germplasm System (NPGS) is a network of institutions and agencies led by the Agricultural Research Service (ARS) of the U.S. Department of Agriculture in the effort to conserve and facilitate the use of the genetic diversity of agriculturally important plants and their wild relatives.

Sally Norton is an Australian plant scientist and national Leader of the Australian Grains Genebank, Agriculture Victoria, in Horsham. Norton has over 20 years' experience in the collection, characterisation and management of plant genetic resources in seedbanks, specialising in crop wild relatives. She is working to establish the Australian Grains Genebank as the national focal point for access to grains germplasm for use in Australia's research and grain crop breeding programs.

<span class="mw-page-title-main">Agriculture in Svalbard</span> Svalbards agriculture

Agriculture in Svalbard – the archipelago containing the world's northernmost permanently inhabited settlements – has a short history, and remains a minor economic factor, but has nonetheless had a culturally and socially significant role, as well as an ecologic impact. Svalbard is home to the Global Seed Vault, which serves to protect the world's biological and agricultural diversity. Polar Permaculture Solutions, AS was formed in January 2015. Polar Permaculture has been focused on producing locally grown food in town, and also with composting food waste.

The Nordic Genetic Resource Center is a plant, farm animal and forest conservation, gene resource guardian, and sustainable use organization under and primarily financed by the Nordic Council of Ministers, and is headquartered in Alnarp, near Malmö, in southern Sweden. NordGen's primary mission is "securing the broad diversity of genetic resources linked to food and agriculture" through "conservation and sustainable use, solid documentation and information work and international agreements".

The National Centre for Plant Genetic Resources: Polish Genebank (NCPGR) is a research unit in the Plant Breeding and Acclimatization Institute – National Research Institute. NCPGR is the coordinator and implementer of the National Crop Plant Genetic Resources Protection Programme. The Programme aims to protect the biodiversity of crop plants endangered by genetic erosion in Poland, and is funded by the Ministry of Agriculture. The main tasks include collection of crop and wild plant populations and varieties threatened by genetic erosion, description and evaluation of collected materials, and preservation of their viability and genetic purity. The Programme is an implementation of provisions laid down in international treaties ratified by Poland:

The Australian Grains Genebank (AGG) is a national center for storing genetic material for plant breeding and research. The Genebank is in a collaboration with the Australian Seed Bank Partnership on an Australian Crop Wild Relatives project. It is located at Grains Innovation Park, in Horsham, Victoria, Australia.

<span class="mw-page-title-main">Plant genetic resources</span>

Plant genetic resources describe the variability within plants that comes from human and natural selection over millennia. Their intrinsic value mainly concerns agricultural crops.

Genetic resources means genetic material of actual or potential value where genetic material means any material of plant, animal, microbial or other origin containing functional units of heredity... Genetic resources thus refer to the part of genetic diversity that has or could have practical use, such as in plant breeding. The term was introduced by Otto Frankel and Erna Bennett for a technical conference on the exploration, utilization and conservation of plant genetic resources, organized by the Food and Agriculture Organisation (FAO) and the International Biological Program (IBP), held in Rome, Italy, 18–26 September 1967.

References

  1. Breman, Elinor; Ballesteros, Daniel; Castillo-Lorenzo, Elena; Cockel, Christopher; Dickie, John; Faruk, Aisyah; O’Donnell, Katherine; Offord, Catherine A.; Pironon, Samuel; Sharrock, Suzanne; Ulian, Tiziana (2021-11-03). "Plant Diversity Conservation Challenges and Prospects—The Perspective of Botanic Gardens and the Millennium Seed Bank". Plants. 10 (11): 2371. doi: 10.3390/plants10112371 . ISSN   2223-7747. PMC   8623176 . PMID   34834734.
  2. "Genebank Standards for Plant Genetic Resources for Food and Agriculture" (PDF). FAO. Rome. 2014. Retrieved 7 June 2023.
  3. Waldhardt, R.; Fuhr-Bossdorf, K.; Otte, A. (2001-11-29). "The significance of the seed bank as a potential for the reestablishment of arable-land vegetation in a marginal cultivated landscape". Web Ecology. 2 (1): 83–87. doi: 10.5194/we-2-83-2001 . ISSN   2193-3081.
  4. Hong, T.D. and R.H. Ellis. 1996. A protocol to determine seed storage behaviour. IPGRI Technical Bulletin No. 1. (J.M.M. Engels and J. Toll, vol. eds.) International Plant Genetic Resources Institute, Rome, Italy. ISBN   92-9043-279-9
  5. "The gatekeepers of Mozambique's community seed banks". UN FAO (Food and Agriculture Organization of the United Nations). Retrieved 2021-09-14.
  6. 1 2 3 van de Wouw, Mark; Kik, Chris; van Hintum, Theo; van Treuren, Rob; Visser, Bert (2009-10-19). "Genetic erosion in crops: concept, research results and challenges". Plant Genetic Resources . 8 (1). NIAB (National Institute of Agricultural Botany) (CUP): 1–15. doi:10.1017/s1479262109990062. ISSN   1479-2621. S2CID   54496219.
  7. 1 2 3 Spooner, David; Treuren, Rob van; Vicente, M. C. de (2005). Molecular markers for genebank management. Rome, Italy: International Plant Genetic Resources Institute (IPGRI). pp. viii+126. hdl:10113/11672. ISBN   978-92-9043-684-3. OCLC   136956590. S2CID   83426985. NADLC# 11672. AGRIS id QJ2007000031. Bioversity PDF. CGIAR hdl : 10568/104976 .
  8. "Nurturing plant legacies: Two groups lend seeds and plants to gardeners". 23 March 2012.
  9. Hills, S.C.; Morris, D.M. 1992. The function of seed banks in northern forest ecosystems: a literature review. Ont. Min. Nat. Resour., Ont. For. Res. Instit., Sault Ste. Marie ON, For. Res. Inf. Pap., No. 107. 25 p.
  10. National Geographic
  11. Frier, Sarah (2012-02-20). "32,000-Year-Old Plant Reborn From Ancient Fruit Found in Siberian Ice". Bloomberg.
  12. Griffiths, Kate (April 2015). "Maximizing the phylogenetic diversity of seed banks". Conservation Biology. 29 (2): 370–81. Bibcode:2015ConBi..29..370G. doi:10.1111/cobi.12390. PMID   25196170. S2CID   20537959.
  13. Maharjan, Shree (February 2018). "Roles and contributions of community seed banks in climate adaptation in Nepa". Development in Practice. 28 (2): 292–302. doi:10.1080/09614524.2018.1418838. S2CID   158910274.
  14. Vernooy, Ronnie (April 2017). "The roles of community seed banks in climate change adaption" (PDF). Development in Practice. 27 (3): 316–327. doi: 10.1080/09614524.2017.1294653 . S2CID   157455756.
  15. Rajasekharan, P. E. (2015-01-01). "Gene Banking for Ex Situ Conservation of Plant Genetic Resources". In Bahadur, Bir; Rajam, Manchikatla Venkat; Sahijram, Leela; Krishnamurthy, K. V. (eds.). Plant Biology and Biotechnology. Springer India. pp. 445–459. doi:10.1007/978-81-322-2283-5_23. ISBN   9788132222828.
  16. "Work starts on Arctic seed vault - CNN.com". www.cnn.com. Archived from the original on 11 February 2007. Retrieved 12 January 2022.
  17. 1 2 3 4 Drori, Jonathan (May 2009). "Why we're storing billions of seeds". TED2009. TED (conference). Archived from the original on 2011-12-08. Retrieved 2011-12-11.
  18. "Banking the world's seeds | Kew". www.kew.org. Archived from the original on 6 July 2008. Retrieved 7 June 2023.
  19. "About the NSW Seedbank - Royal Botanic Gardens & Domain Trust - Sydney, Australia". Archived from the original on 2013-06-01. Retrieved 2012-10-02.
  20. "SCIENTISTS DIED GUARDING SEEDS DURING WWII". May 13, 1992.
  21. David Ehrlich (July 27, 2022). "'One Man Dies a Million Times' Review: A Haunting Portrait of Preservation at the End of the World". Indiewire . Retrieved August 2, 2022.
  22. Save the Seeds Movement of the Uttarakhand Himalayas, India Archived June 30, 2015, at the Wayback Machine
  23. "National Center for Genetic Resources Preservatio". Archived from the original on 12 November 2011. Retrieved 7 June 2023.
  24. "Desert Legume Program (DELEP) | Home". 24 January 2019.
  25. "National Center for Plant Genetic Resources of Ukraine - Інститут рослинництва ім. В. Я. Юр'єва НААН". yuriev.com.ua. Retrieved 2022-05-18.
  26. "Військові рф повністю знищили єдиний в Україні генетичний банк рослин". www.ukrinform.ua (in Ukrainian). 16 May 2022. Retrieved 2022-05-18.
  27. "Ukraine's agricultural research is threatened by the war". The Economist. Retrieved 2022-05-18.
  28. Salinier, Jérémy; Lefebvre, Véronique; Besombes, Didier; Burck, Hélène; Causse, Mathilde; Daunay, Marie-Christine; Dogimont, Catherine; Goussopoulos, Juliette; Gros, Christophe; Maisonneuve, Brigitte; McLeod, Louis (2022-01-27). "The INRAE Centre for Vegetable Germplasm: Geographically and Phenotypically Diverse Collections and Their Use in Genetics and Plant Breeding". Plants. 11 (3): 347. doi: 10.3390/plants11030347 . ISSN   2223-7747. PMC   8838894 . PMID   35161327.
  29. Pellegrini, Pablo A.; Balatti, Galo E. (2016-12-01). "Noah's arks in the XXI century. A typology of seed banks". Biodiversity and Conservation. 25 (13): 2753–2769. Bibcode:2016BiCon..25.2753P. doi:10.1007/s10531-016-1201-z. hdl: 11336/46868 . ISSN   1572-9710. S2CID   2545366.
  30. Avesta, Vendidad, Fargard 2:24-28
  31. Teutonic Mythology by Viktor Rydberg (1906), v. 1, p. 307-43; v. 2, p. 380-89

Further reading