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Glossary

• Cold stratification
   i.e. a moist cold treatment. Type of pretreatment most effective in removing physiological dormancy. It approximates to the conditions of overwintering in nature.
• Cotyledon
  Modified leaf or leaves of the embryo or seedling, which may contain the stored food reserves of the seed (= seed leaf). They are formed at the first node or at the upper end of the hypocotyl.
• Dormancy

  The term “dormancy” refers to a condition in a viable seed which prevents it from germinating when supplied with the factors normally considered adequate for germination - suitable temperature, moisture and gaseous environment.

  A physiological state in which a seed predisposed to germinate does not, even in the presence of favourable environmental conditions. 

• Embryo
  The non-self-supporting immature organism formed from the zygote by cell division and differentiation; the rudimentary plant within the seed.
• Exogenous Dormancy
  Seeds with hard, cutinised seedcoats that completely prevent the imbibition of water. Without imbibition renewal of embryo growth and germination are impossible. Pretreatment to overcome physical seedcoat dormancy includes physical and biological methods, dry heating and soaking in water or chemical solutions. Commonly called scarification.
• Germination

  Germination transform the embryo within the seed into the independent seedling. For the purpose of laboratory testing, germination is defined as the emergence and development from the seed embryo of those essential structures which are indicative of the seed's capacity to produce a normal plant under favourable conditions (Justice 1972).

  In general, resumption of active growth in the embryo of a seed as demonstrated by the protrusion of the radicle. In seed testing (ISTA definition), resumption of active growth in an embryo which results in its emergence from the seed and development of those structures essential to normal plant development. 

  JUSTICE, O.L. (1972): Essentials of seed testing. In Seed Biology Vol. 3 (Ed. T.T. Kozlowski). Academic Press New York and London, 301–370. 

• Hard seeds
  Seeds which remain hard and ungerminated at the end of a prescribed test, because they have not absorbed water due to an impermeable seedcoat.
• Imbibition
  The mechanism of initial water uptake by seeds; the taking up of fluid by a colloidal system.
• Longevity
  The period for which seed can be stored, i.e. the period for which the germination and viability of the seed remain on acceptable levels.
• Orthodox seeds

  Seeds which can be dried down to a low MC of around 5% (wet basis) and successfully stored at low or sub-freezing temperatures for long periods. We can distinguish two main types of orthodox seeds: hard-coated orthodox seeds and orthodox seeds without hard seedcoats.

  Term used to describe species of which the seeds can be dried down to a low moisture content of around 5% and successfully stored at low or sub-freezing temperatures for long periods. 

• Recalcitrant seeds

  Seeds which cannot survive drying below a relatively high moisture content (often in the range 20–50% wet basis) and which cannot be successfully stored for long periods.

  Term used to decribe species of which the seeds cannot survive drying below a relatively high moisture content and cannot be successfully stored for long periods. 

• Scarification

  Any treatment which destroys or reduces seedcoat impermeability (Bonner 1984 a). It includes physical and biological methods, dry heating and soaking in water or chemical solutions. 

  Disruption of seed coats, usually by mechanical abrasion or by brief chemical treatment in a strong acid, to increase their permeability to water and gases, or to lower their mechanical resistance. 

  BONNER, F.T. (1984 a): Glossary of seed germination terms for tree seed workers. USDA Forest Service. Gen. Tech. Rep. SO-49, Southern Forest Experiment Station. 

• Seed
  A fertilized and mature ovule which contains an embryo and nutritive tissue and is enclosed in protective layers of tissue (seed coat).
• Stratification
  Practice of burying seeds in moist medium, often in alternate layers to overcome dormancy; commonly applied to any technique which keeps seeds in a cold and moist environment.