germination

from Wikipedia, the free encyclopedia
Sunflower seedlings , three days after (Epigeic) germination

In botany, germination is both the first stage of ontogenesis in seeds and the sprouting of the perennial organs such as rhizomes , tubers , bulbs , brood buds (bulbils) or in pollen and spores . The hallmark is the end of dormancy or dormancy ; Unwanted germination of grain is called outgrowth .

In a narrower sense, however, the beginning of the development of the seed of the seed plants ( spermatophyta ) is called germination. It encompasses the process of growth of the embryo in the fertile seed from the emergence of the radicle to the complete development of the seedling .

Types of germination

Depending on the species, a distinction is made between an epigeic or hypogean germination type .

Epigeic germination

Epigeic germination

During epigean (epi, Greek: over / on; gae, Greek: earth) germination, the hypocotyl (young section between the root and cotyledons ) stretches . It forms a typical Hypokotylhaken, which breaks through the surface and thereby the seed leaves ( cotyledons ) raises. The cotyledons are photosynthetically active until the primary leaves (= first subsequent leaves) are formed and later die off. Examples of epigeic germination are radishes , beech , castor , potatoes , rapeseed and sunflower .

Hypogean germination

Hypogean germination

During the hypogean (hypo, gr .: under; gae, gr .: earth) germination, the epicotyl stretches so that the cotyledons remain in the soil. The first photosynthetically active leaves are the primary leaves. Examples of hypogean germination are pea , fire bean , oak, and date palm .

Requirements for germination

For the germination of seeds water , warmth and oxygen are necessary, sometimes also light ( light germs ) or darkness ( dark germs ). Different types of seeds need different germination conditions, especially the right temperature is important to the dormancy overcome. Some seeds can even germinate after frost or forest fires. The seed is often very dry and must first absorb a large amount of water so that its metabolism can start. For the first growth processes, the nutrients in the seed, e.g. B. oil or proteins , used as food. Hydrolases break down these nutrients and enable the embryo to move towards the light by growing the stem and leaves . If these substances are used up and the light is sufficient, it gains the necessary energy from photosynthesis.

Germ release

Seeds are stored in a cool, airy and dry place to preserve germination. By sowing in the earth, the seeds come into contact with moisture from all sides, which leads to further development of the embryo after a while. As a rule, seeds for cultivated and garden plants are brought underground at the beginning of the warm season, i.e. in spring, in order to trigger their germination. The terms 'warm germs' (also 'normal germs ' ) and ' dark germs ' are therefore rarely used for such seeds.

Other seeds, on the other hand, require special conditions in order for them to germinate, which are emphasized again by terms such as 'cold germs', 'light germs', 'fire germs' or the indication that such seeds have to be 'pre-soaked' or 'stratified' .

The exact information on pretreatment, application depth, temperatures and times for the best germination are defined in the culture and cultivation instructions for the respective seeds.

Pre-swelling

When sown directly, particularly hard kernels very slowly absorb the moisture from the soil. In order to accelerate water absorption and thus germination, the seeds are placed in a water bath for a few hours before they are sown. Examples: lupins , sweet peas .

Sometimes the water uptake of the seeds in the soil is referred to as 'pre-swelling', if the seeds are cold germs and these should first absorb water over a certain period of time before being activated by cold of below 0 ° C at a higher temperature.

Light germination

The light germs need brightness in order to germinate. The seeds are not covered with soil when sowing. They are only lightly pressed into the earth. This gives them good contact with the damp earth. The seeds need light, but not direct sunlight. Examples: thyme , basil , lettuce , celery , poppy seeds , lavender , forget-me-nots , columbines .

Dark germination

The seeds of the dark germinators begin to germinate in the absence of light. To do this, the seeds are completely covered with earth. The seeds are sown in holes or grooves or spread over an area. Then it is covered with a layer of earth. The thickness of the layer depends on the size of the seeds. Finally, the earth is pressed lightly. If the seed is too tightly coated, it will be harder to breathe. 23

Cold germination

As Kaltkeimer , formerly Frost germinate called, refers to plants whose seeds a cold or frost must have gone through before germination is triggered. In the garden planting area, these are mostly alpine perennials from colder areas that have thicker and harder seed coats than usual.

After the seeds are swollen or germinated by moisture, low temperatures of −5 to +5 degrees Celsius after 4 to 8 weeks ensure that the ratio of germ-inhibiting and germ-promoting substances in the seed shifts in favor of germ-promoting substances and the seed sprouts. Frost germs are therefore sown in September to November, some varieties only in late winter.

Cold germs which are sown too late and cannot go through a sufficiently long cold period will only germinate after the next winter.

If the seeds are exposed to artificial cold, e.g. B. in a refrigerator, this is called stratification . 24

Some cold germs need different temperatures in different development phases in order to germinate. The absorption of water from the surrounding soil is the first phase, the initialization for germination is the second phase and the third phase until the leaves are formed.

Typical cold germs and temperatures required for germination

  • Winter wheat ( Triticum sp) 0 to 1 ° C; 2 to 4 ° C slows germination
  • Hemp ( Cannabis sp) 0 to 1 ° C
  • Rye ( Secale cereale ) 0 to 1 ° C
  • Poppy seeds ( Papaver sp) 1 to 5 ° C
  • Spinach ( Spinacia oleracea ) 1 to 5 ° C
  • Sugar beet ( Beta vulgaris subsp. Vulgaris ) 1 to 5 ° C
  • Cloudberry ( Rubus chamaemorus ) above 1 ° C for 13 weeks; germinate at over 18 ° C after 270 days of stratification
  • Wild garlic ( Allium ursinum ) 1st phase: 15 to 20 ° C, 2nd phase: −4 to 2 ° C for 4 to 6 weeks, 3rd phase: 10 to 12 ° C
  • Real cowslip (Primula veris) 3 to 7 ° C for 2 to 3 weeks
  • Pasque Flower ( Pulsatilla vulgaris )
  • Christmas rose ( Helleborus niger ) 1st phase: 10 to 15 ° C for 1 week, 2nd phase: 0 to 5 ° C for 1 week, 3rd phase: above 15 ° C

Warm germinator

Warm germs can be frost-resistant, but also cannot withstand frost. To activate germination, they need temperatures of +5 ° C and more for one to several weeks. Frost-resistant species can be sown in thawed soil as early as February, such as B. Field beans. Species that are not frost-resistant are only sown in May or planted out as small plants that have already been grown in greenhouses, e.g. B. Corn.

Typical warm germs and their germination temperatures

  • Bean , i. e. S. broad bean ( Vicia faba ) 5 to 11 ° C; 10 ° C for 5 to 10 days
  • Corn ( Zea mays ) 5 to 11 ° C
  • Tobacco ( Nicotiana sp) 11 to 16 ° C
  • Tomato ( Solanum lycopersicum ) Outdoor: 11 to 16 ° C
  • Pumpkin ( Cucurbita maxima ) 11 to 16 ° C, ( Cucurbita pepo ) 15 to 20 ° C for 8 to 12 days
  • Cucumber ( Cucumis sp) Outdoor: above 16 ° C; Greenhouse: above 25 ° C
  • Melon depending on the type: over 16 ° C; 20 to 25 ° C for 10 to 14 days
  • Basil ( Ocimum basilicum ) depending on the variety over 16 ° C to over 25 ° C

Fire Bucket

Fire germs such as the Australian cylinder cleaner or the real acacia are plants whose seeds can only germinate through a fire. The fire incidents necessary for this are divided into forest fires, pasture fires (grassland) or bush fires, which in turn are divided into ground fires (soil / humus layer, <100 ° C over a long period), surface fires (vegetation without treetops, approx. 500 ° C) and crown fires (Vegetation with treetops,> = 1000 ° C) can be distinguished.

In a narrower sense, fire germs are those plants whose seeds break their dormancy due to the heat event , for example plants from the legume families ( Fabaceae ) and the rockrose plants ( Cistaceae ). The seeds may have been formed by a plant decades ago or (estimated) more than a hundred years ago, e.g. B. Bohemian cranesbill Geranium bohemicum , L. and Geranium bohemicum subsp. depraehensum E.G. Almq. 1916.

In a broader sense, however, those plants are also counted among the fire germs, the seeds of which are only stimulated to germinate by substances generated by the fire , for example smoke or coal.

Most of the time, fire buckets are easily flammable themselves . They can burn off almost completely, which means better light conditions and faster growth for the seedlings and young plants. Stored essential oils and resins , so-called secondary ingredients, improve the flammability and lower the flash point .

Some plants are known to produce two different seeds. One seed variant experiences the condition for germ release once in the course of the year, while the second seed variant begins to germinate immediately after a fire, for example species of the genus Rockrose Cistus .

Artificial germ release

The artificial triggering of the germination of cold germs by cold treatment of the seeds is called stratification .

However, this does not include vernalization , also known as Jarowization, which is defined differently , which makes it possible to grow cold germs such as winter cereals even in areas with a short vegetation period (long winters) and winter soil temperatures below −20 ° C, where even such plants or theirs Seeds irreversibly lose their ability to germinate.

In a broader sense, the renewal of vegetation by controlled, deliberately set fires, e.g. B. to maintain a phrygana carried out every 10 years, referred to as artificial germ release.

Finally, to accelerate germination, some seeds are also treated with gibberellic acid , which may trigger immediate germination.

Picture gallery

Biochemical processes

During germination, u. a. the following biochemical processes:

  • Absorption of water
  • Swelling of the seed coat, making it soft and / or tearing open
  • Formation of starch- and protein-degrading enzymes in the seedling and in the seed coat
  • Degradation of storage substances such as fats, starches or proteins in the endosperm [in angiosperms (bedecktsamern) ] or in the perisperm [in gymnosperms (naked samers) ], especially of
    • Fats, e.g. B. oils, in carbohydrates
    • Carbohydrates, e.g. B. starch or cellulose, in soluble dextrin and simple sugars
    • solid protein, e.g. B. Aleuron , in soluble albuminates
  • Metabolism of the degraded storage substances, accompanied by heat development and breathing
  • Formation of new cells , for example the cotyledon , which becomes visible above ground (in the case of epigeous germination) and absorbs oxygen, as well as the radicles
  • Formation of the first true leaves
  • Providing the new plant with water and nutrients through the roots and with oxygen through the leaves

See also

Wiktionary: germination  - explanations of meanings, word origins, synonyms, translations

proof

  • Gerhard Wagenitz : Dictionary of botany. The terms in their historical context . 2nd expanded edition. Spectrum Academic Publishing House, Heidelberg / Berlin 2003, ISBN 3-8274-1398-2 , p. 167-168 .

Individual evidence

  1. a b c d e f g h i Bertelsmann Volkslexikon. Bertelsmann Verlag (ed.), Gütersloh, October 1956, 24th edition, column 933.
  2. K. Martini, Das Saatgut. In: Haniel GmbH (ed.), Haniel's garden books (brochure series), brochure no. 7 of 28 'Summer flowers in the garden', p. 9, Mannheim undated (date of printing of the enclosed order form: December 1963).
  3. a b c d e f counselor. Gardening practice. Questions and answers. Medien Kommunikation Unna (ed.), Komet Verlag, Cologne, undated (approx. 2006), ISBN 978-3-89836-539-0 , p. 44.
  4. a b Christiane Breder: Cold, warm, light or dark. How seeds can best germinate. Gartenfreunde.de, accessed on April 11, 2014 .
  5. a b c d e Gartenland Aschersleben (Ed.): Good to know! In: GartenMagazin 2013 (magazine), Essen 2013, p. 24. Flash version online , accessed April 11, 2014.
  6. a b Benary (ed.): Christmas rose. Helleborus niger. (Culture instructions on seed package N 3350), Ernst Benary Samenzucht, Hann. Münden 2013.
  7. a b c d e f g h i j Sperli (Ed.): On your marks , get set - sowing! (Leaflet), Everswinkel o. J. (approx. 2013), p. 3. PDF version online , accessed April 11, 2014.
  8. a b Gartenland-Aschersleben (Ed.): Sowing tips. (Cultivation instructions on seed package No. 20914), 2013.
  9. a b c d e f g h i j k l m n o p q r s t Lexicon in two volumes. AZ. In: 'Verlag - Lexikon AZ current reliable' Porz am Rhein (licensee), Stauffacher Verlag AG, Zurich 1970, column 2030.
  10. ^ Rubus chamaemorus. hortipedia, October 30, 2013, accessed April 11, 2014 (description of the species).
  11. Carol C. Baskin, Jerry M. Baskin: Propagation protocol for production of container Rubus chamaemorus L. plants. University of Kentucky, Lexington Kent. In: Native Plant Network. University of Idaho, College of Natural Resources, Forest Research Nursery. Moscow ID 2002. Synopsis ( Memento of September 27, 2007 in the Internet Archive ), ISSN  1522-8339 .
  12. Sperli (Ed.): Real cowslip . (Culture instructions on seed package No. 86369), Everswinkel 2013. Image file ( Memento from April 13, 2014 in the Internet Archive )
  13. a b c d e Gartenland Aschersleben (Hrsg.): Sowing calendar. Vegetables, herbs, flowers. In: GartenMagazin 2013 (magazine), Essen 2013, pp. 22–23. Flash version online , accessed April 11, 2014.
  14. Dimitrios S. Kailidis, Stephanos Markalas: forest, bush and pasture fires in Greece. In: AFZ - Allgemeine Forstzeitschrift für Waldwirtschaft und Umweltvorsorge, Volume 44, 1989, Issue 4, pp. 96-97, BLV Verl.-Ges., Munich 1989, ISSN  0936-1294 .
  15. a b David Bösch: Adaptation of Mediterranean Plants to Fire. In: Corsica 2006, Institute for Botany, University of Innsbruck, 2006. PDF version online ( Memento from March 4, 2016 in the Internet Archive ), accessed April 22, 2014.
  16. a b Stefanie König: The dwarf shrub societies. Seminar contribution in the module "Terrestrial Ecosystems" (2101–232), Botanical Institute (210), University of Hohenheim, Stuttgart January 10, 2013, panels 09.5 and 09.8. PDF version online ( memento of August 8, 2014 in the Internet Archive ), accessed April 22, 2014.
  17. KV Ossian Dahlgren: Geranium bohemicum L. × G. bohemicum deprehensum Erik Almq. A green-white-marbled bastard. With summary in English. In: Mendelska sallskapet i Lund (Ed.), Hereditas, Volume 4, Issue 1–2, February 1923, ISSN  0018-0661 , pp. 239–250, doi : 10.1111 / j.1601-5223.1923.tb02962.x , access April 22, 2014.
  18. ^ A b Alfred Thomas Grove, Oliver Rackham: The nature of Mediterranean Europe. An ecological history . 2nd corrected edition. Yale University Press, New Haven, Conn./London 2003, ISBN 0-300-10055-8 , Chapter 13. Fire: Misfortune or adaptation ?, pp. 217-241 (English).