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Chapter: 11 th 12th std standard Bio Botany plant tree Biology Higher secondary school College Notes

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Factors necessary for seed gamination

A number of factors are required for the process f germination . They are of two types-external and internal.

Factors necessaryf for seed gamination

 

A number of factors are required for the process f germination . They are of two types-external and internal.

 

External factors.

 

1. Water

 

Seeds are generally highlly dehydrated with only 6-15% of water content in their cells.Therefore they have low physiological activity. Water provides sufficent hydration to the concentrated protoplasm of the transport gases, a cause hydrolysis of reserve food nd its trnansport and allow embryo cells to grow in size.

 

2. Oxygen

 

Oxygen is essential for aerobic respiration to release energy for the metabolic activities. Therefore, with the exception of the few plants. (eg. rice, Typha etc) seeds usually require oxygen or good aeration for their germination.

 

3. Temperature

 

Seeds require a definite temperature range withinwhich they germinate. Commonly seeds germinate within temperature range of 50C to 400C. However, the optimum temperature or seed germination lies between 25-300C for most of the species.

 

4. Light

 

Light is not an essential factor for the germination of most of the seeds. However some are light sensitive and their germination is influenced by the presence or absence of light.

 

Internal factor

 

1. Maturity of embryo: The seeds of some plants, when shed, contain immature embryo. Such seeds germinate only after maturation of their embryo.

 

2. After ripening: The freshly shed seeds of some plants may not possessthe required hormones for the growth of embryo, such seeds germinate only after the maturation of their embryo.

 

3. Viability:Usually seeds remain viable or living only for a particular period. The viability of seeds range from a few days (eg. Oxalis) to more than one hundred years. (eg. Trifolium). Maximum viability (i.e., 1000 years) has been recorded in lotus seeds. Seeds germinate only within the period of viablity.


4. Dormancy: Seeds of many plants are dormant at the time of shedding. Seed dormancy may be due to various reasons like impermeability, toughness of seed coats, presence of growth inhibitors etc. Such seeds germinate only after natural breakage of dormancy.


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