Scarification (botany)
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Scarification in
botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek w ...
involves weakening, opening, or otherwise altering the coat of a
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
to encourage
germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...
. Scarification is often done mechanically, thermally, and chemically. The seeds of many plant species are often impervious to water and gases, thus preventing or delaying germination. Any process designed to make the testa (seed coat) more permeable to water and gases is known as scarification. Scarification, regardless of type, works by speeding up the natural processes which normally make seed coats permeable to water and air. For
drupe In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part (exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or '' pyrena'') of hardened endocarp with a seed (''kernel'') ...
s (stone fruits), scarification also extends to weakening or removal of the hard
endocarp Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. They are found in three main anatomical categories: aggregate fruits, multiple fruits, and simple fruits. Agg ...
shell around the seed.


Types

Regardless of the method, scarified seeds do not store well and need to be planted quickly, lest the seeds become unviable.


Mechanical

The most common type of scarification is mechanical scarification. In mechanical scarification, the testa is physically opened to allow moisture and air in. Seed coats may be filed with a metal file, rubbed with sandpaper, nicked with a knife, cracked gently with a hammer, or weakened or opened in any other way.


Heat


Hot water

The
imbibition Imbibition is a special type of diffusion that takes place when liquid is absorbed by solids-colloids causing an increase in volume. Water surface potential movement takes place along a concentration gradient; some dry materials absorb water. A ...
of water through seed shell membrane is affected by water temperature. Species that can withstand hot water will sprout faster under that condition than from cold tap water. The
North Carolina State University North Carolina State University (NC State) is a public land-grant research university in Raleigh, North Carolina. Founded in 1887 and part of the University of North Carolina system, it is the largest university in the Carolinas. The universit ...
recommends placing the seeds in boiling water and letting them soak while the water cools to room temperature, and then remove the seeds from the water and sow. The
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
of floating seeds must be compensated with
gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
to submerge them, this can be achieved with an
infuser A tea infuser is a device in which loose, dried tea leaves are placed for steeping or brewing, in a mug or a teapot full of hot water; it is often called a teaball or tea maker, and sometimes a tea egg. The tea infuser gained popularity in the ...
. Hot water scarification can be combined with chemical scarification, but might require protective equipment against formed gases. Hot water treatment is also used for removal of pathogens. Placing seeds in 90 °C for 90 seconds followed by dip in cold water for 30 seconds kills the human pathogens ''
Escherichia coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' O157:H7 and ''
Salmonella ''Salmonella'' is a genus of rod-shaped (bacillus) Gram-negative bacteria of the family Enterobacteriaceae. The two species of ''Salmonella'' are ''Salmonella enterica'' and ''Salmonella bongori''. ''S. enterica'' is the type species and is fur ...
''. A variety of plant pathogens are also be killed by hot water treatment.


Thermal

In some
chaparral Chaparral ( ) is a shrubland plant community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranean c ...
plant communities, some species' seeds require fire and/or smoke to achieve germination. An exception to that phenomenon is
western poison oak ''Toxicodendron diversilobum'' (syn. ''Rhus diversiloba''), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family, Anacardiaceae. It is widely distributed in western North America, inhabiting coni ...
, whose thick seed coatings provide a time delayed effect for germination, but do not require fire scarification.


Chemical

Chemical scarification involves the use of one or more chemicals to promote germination. It can involve imbibing or soaking seeds in precisely concentrated acidic or basic solutions for varying amounts of time. Chemicals such as
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
or even household chemicals can be used to affect this process. Chemical scarification can also be achieved through the use of nutrient salts such as
potassium nitrate Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitrat ...
. Common chemicals that don't require special permission in solution form: *
Acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
s: ** 25-75%
phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
solution. 25% phosphoric acid is commonly sold by
grow shop A grow shop or growshop is a retail store that sells equipment and supplies for growing plants indoors. Types include stores selling hydroponic systems for horticulture, and those devoted to cannabis cultivation. History In the 1950s, marijuan ...
s. 75% phosphoric acid is commonly sold by
homebrewing Homebrewing is the brewing of beer or other alcoholic beverages on a small scale for personal, non-commercial purposes. Supplies, such as kits and fermentation tanks, can be purchased locally at specialty stores or online. Beer was brewed dom ...
shops. ** 15%
sulphuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
swimming pool sanitation Swimming pool sanitation is the process of ensuring healthy conditions in swimming pools. Proper sanitation is needed to maintain the visual clarity of water and to prevent the transmission of infectious waterborne diseases. Methods Two distinct ...
chemical. Also a drain cleaner. * Bases **
Sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...
household chemical Household chemicals are non-food chemicals that are commonly found and used in and around the average household. They are a type of consumer goods, designed particularly to assist cleaning, house and yard maintenance, cooking, pest control and ge ...
for drain cleaning. * Other ** 3%
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%†...
– common skin disinfectant. Pure forms of the chemicals listed above is unnecessary and often require special permission to obtain.


Common uses

Because scarified seeds tend to germinate more often and in less time than unaltered seeds, scarification finds use not just in industry but on the small scale. In home gardens, for example, the seeds of plants which are otherwise difficult to grow from seed may be made viable through scarification. The thawing and freezing of water, fire and smoke and chemical reactions in nature are what allow seeds to germinate but the process can be sped up by using the various methods described thus far. The common objective is opening the testa and allow air and water into the seed. In horticulture, scarification is often used to facilitate the controlled and uniform germination of seed lots.


Research

A paper was published by the New Zealand Journal of Experimental Agriculture and stated that the seeds they examined in their study germinated only 30% under the preferred conditions, yet when they were treated chemically with concentrated
sulphuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
or mechanically scarified, the germination rate increased to more than 80%. Another study was done on four different types of
Great Basin The Great Basin is the largest area of contiguous endorheic basin, endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California ...
lupine species to see the effect different methods of scarification would have on said seeds. The longspur lupine, silvery lupine, hairy bigleaf lupin, and silky lupine were the four species experimented on throughout the study. To summarize the experiment produced various results, due to the difference in species. The Silky lupine's highest germination rate was achieved via mechanical scarification at 66.4%, opposed to its 22% germination rate found in the control group. Using thermal and chemical scarification, germination increased to 48.8% and 44% respectively. Interestingly enough 68% of the Longspur lupine seeds germinated in the control group and all scarification methods decreased the success rate of germination. The silvery lupine had 52% of its control group germinate but through mechanical scarification it rose to 85.2%. Finally the hairy bigleaf lupine's control group germination rate was 32% yet when treated with sulfuric acid it rose to 76.8% showing the varying results of the experiment.


See also

*
Stratification (seeds) In horticulture, stratification is a process of treating seeds to simulate natural conditions that the seeds must experience before germination can occur. Many seed species have an embryonic dormancy phase, and generally will not sprout until this ...


References

{{DEFAULTSORT:Scarification (Botany) Horticulture