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How can a hard seed coat prevent germination?
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seed
Fruit and seeds of the southern magnolia (Magnolia grandiflora). The fruit is an aggregate of follicles, and each follicle bears a single red seed.
A hard testa, or seed coat, can prevent germination through three primary mechanisms:
- Mechanical Restriction: The hard coat may physically prevent the embryo from expanding as it begins to grow.12
- Water Impermeability: The coat may block the entrance of water, which is essential for the metabolic processes required for germination.12
- Gas Exchange Impediment: The coat may restrict the passage of gases, specifically preventing the embryo from obtaining the oxygen necessary for respiration.12
In nature, these barriers are often overcome over time through weathering, microbial attack, or passage through an animal's digestive tract. In horticulture and agriculture, humans use a process called scarification to artificially weaken or damage the seed coat. This can be achieved through mechanical means, such as abrasion, or chemical treatments, such as exposure to sulfuric acid or hot water, to restore permeability to water and gases.13