Leopold (1961) has recognised four types of senescence:
1. Overall senescence
2. Top senescence
3. Deciduous senescence
4. Progressive senescence

1. Vernalization shortens the vegetative period and induces the plant to flower earlier.
2. It increases the cold resistance of the plants.
3. It increases the resistance of plants to fungal disease.
4.  Plant breeding can be accelerated.

Factors causing dormancy of seeds:
1. Hard though seed coat causes barrier effect as impermeability of water, gas and restriction of the expansion of embryo prevents seed germination.
2. Many species of seeds produce imperfectly developed embryos called rudimentary embryos which promotes dormancy.
3. Lack of specific light requirement leads to seed dormancy.

1) In most of the plants" there is sharp rise in respiration rate near·the end of the development of fruit, called climacteric rise.
2) Such fruits are called climacteric fruits. The ripening on demand can be induced in these fruits by using ethylene.
Eg: Tomato, Apples, Banana, Mango, etc.,

Five major groups of hormones viz., auxins, gibberellins, cytokinins, ethylene and abscisic acid are presently known to coordinate and regulate growth and development in plants.