germination

1 the process whereby seeds or spores sprout and begin to grow [syn: sprouting]

2 the origin of some development; "the germination of their discontent"

English

Pronunciation

• Rhymes: -eɪʃǝn

Noun

1. The process of germinating; the beginning of vegetation or growth in a seed or plant; the first development of germs, either animal or vegetable.

Germination is the process whereby growth emerges from a period of dormancy. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However, the growth of a sporeling from a spore, for example the growth of hyphae from fungal spores, is also germination. In a more general sense, germination can imply anything expanding into greater being from a small existence or germ.

Seed germination

Germination is the growth of an embryonic plant contained within a seed, it results in the formation of the seedling. The seed of a higher plant is a small package produced in a fruit or cone after the union of male and female sex cells. Most seeds go through a period of quiescences where there is no active growth, during this time the seed can be safely transported to a new location and/or survive adverse climate conditions until it is favorable for growth. The seed contains an embryo and in most plants stored food reserves wrapped in a seed coat. Under favorable conditions, the seed begins to germinate, and the embryonic tissues resume growth, developing towards a seedling.

Requirements for seed germination

The germination of seeds is dependent on both internal and external conditions. The most important external factors include: temperature, water, oxygen and sometimes light or darkness. If the soil is waterlogged or the seed is buried within the soil, it might be cut off from the necessary oxygen it needs. Oxygen is used in aerobic respiration, the main source of the seedling's energy until it has leaves, which can photosynthesize its energy requirements.

Epigeous

In epigeous (or epigeal) germination, the hypocotyl elongates and forms a hook, pulling rather than pushing the cotyledons and apical meristem through the soil. Once it reaches the surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlings into the air. Beans, tamarind, and papaya are examples of plant that germinate this way.

During germination, the tube cell elongates into a pollen tube. In the flower, the pollen tube then grows towards the ovule where it discharges the sperm produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants.

Spore germination

Germination can also refer to the emergence of cells from resting spores and the growth of sporeling hyphae or thalli from spores in fungi, algae, and some plants.

Conidia are the asexual reproductive spores of fungi, which germinate under specific conditions. From the germinating conidia different cells are formed. The most common one is the germ tube. The germ tube will grow and developed into the hyphae. During germination, conidial may produce conidial anastomosis tubes, those are different from conidial anastomosis tubes because they are thinner, shorter, lack branches, exhibit determinate growth, and home toward each other. Both cells have a tubular shape, but the conidial anastomosis form a bridge that allows fusion between conidia.

Resting spores

In resting spores, germination involves cracking the thick cell wall of the dormant spore. For example, in zygomycetes the thick-walled zygosporangium cracks open and the zygospore inside gives rise to the emerging sporangiophore. In slime molds, germination refers to the emergence of amoeboid cells from the hardened spore. After cracking the spore coat, further development involves cell division, but not necessarily the development of a multicellular organism (for example in the free-living amoebas of slime molds).

Zoospores

In motile zoospores, germination frequently means a lack of motility and changes in cell shape, which allow the organism to become sessile.

Ferns and mosses

In plants such as bryophytes, ferns, and a few others, spores germinate into independent gametophytes. In the bryophytes (e.g. mosses and liverworts), spores germinate into protonemata, similar to fungal hyphae, from which the gametophyte grows. In ferns, the gametophytes are small, heart-shaped prothalli that can often be found underneath a spore-shedding adult plant.

See also

• Lily Seed Germination Types
• Seedling
• Sprouting

References

External links

• Sowing Seeds A survey of seed sowing techniques.
• Seed Germination: Theory and Practice, Norman C. Deno, 139 Lenor Dr., State College PA 16801, USA. An extensive study of the germination rates of a huge variety of seeds under different experimental conditions, including temperature variation and chemical environment.