Physiological effect:
1) Cytokinin promotes cell division in the presence of auxin (IAA).
2) Induces cell enlargement associated with IAA and gibberellins
3) Cytokinin can break the dormancy of certain light-sensitive seeds like tobacco and induces seed germination.
4) Cytokinin promotes the growth of lateral bud in the presence of apical bud.
5) Application of cytokinin delays the process of aging by nutrient mobilization.
6) It is known as Richmond Lang effect.
7) Cytokinin
(i) increases rate protein synthesis
(ii) induces the formation of inter-fascicular cambium
(iii) overcomes apical dominance
(iv) induces formation of new leaves, chloroplast and lateral shoots.
8) Plants accumulate solutes very actively with the help of cytokinins.

Chemical warfare (CW) involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from nuclear warfare, biological warfare and radiological warfare, which together make up CBRN, the military acronym for chemical, biological, radiological, and nuclear (warfare or weapons), all of which are considered "weapons of mass destruction" (WMDS), a term that contrasts with conventional weapons.

old age is called" senescence 'in plants,  senescence refers to all col1ective, progressive and deteriorative processes which ultimately lead to complete loss of organization and 'function.'
Four types of senescence:
I) Overall senescence
2) Top senescence
3) Deciduous senescence ,
4) Progressive senescence
Overall senescencer This kind of senescence occurs in annual plants when entire plant get 'affected and dies . Eg: Wheat and Soybean. It also occurs in few perennials also'. Eg: Agave and Bamboo.
Top senescence: It occurs in aerial parts of plants. It 'is common in perennials, underground and root system remains viable. Eg: Banana and Gladiolus.
Deciduous senescence: It is common in deciduous plants and occurs only in leaves of plants, bulk of the stein and root system remains alive. Eg: Elm and Maple.
Progressive senescence: This kind of senescence is gradual. First it occurs in old leaves followed by new leaves then stem and' finally root system. It is common in annuals.
Physiology of Senescence:
1) Cells undergo changes in structure.
2) Vacuole of the cell acts as lysosome and secretes hydrolytic enzymes.
3) The starch content is decreased in the cells.
4) Photosynthesis is reduced due to loss of chlorophyll accompanied by synthesis and accumulation of anthocyanin pigments therefore the leaf becomes red .
5) There is a marked decrease in protein content in the senescing organ.
6) RNA content of the leaf particularly rRNAlevel is decreased in the cells due to increased activity of the enzyme RNA ase.
7) DNA molecules in senescencing leaves degenerate by the increased activity of enzyme DNA ase. 
Factors affecting Senescence:
1) ABA and ethylene accelerate senescence while auxin and cytokinin retard senescence.
2) Nitrogen deficiency increases . senescence whereas nitrogen supply retards senescence.
3) High temperature. accelerates senescence but low temperature retards senescence.'
4) Senescence is rapid in dark'than iti light.
5) Water stress 'leads to accumulation of ABA leading to senescence.
Programned cell death:
Senescence is controlled by plants own genetic programme. Death of the plant or plant part consequent to senescence is called programmed cell Death. In short senescence of an individual cell is called PCD.

(i) Senescence is controlled by plants own genetic programme and death of the plant or plant part consequent to senescence is called Programmed Cell Death.
(ii) In short senescence of an individual cell is called PCD.
(iii) The proteolytic enzymes involving PCD in plants are phytaspases and in animals are caspases.
(iv) The nutrients and other substrates from senescing cells and tissues are remobilized and reallocated to other parts of the plant that survives.
(v) The protoplasts of developing xylem vessels and tracheids die and disappear at maturity to make them functionally efficient to conduct water for transport.
(vi) In aquatic plants, aerenchyma is normally formed in different parts of the plant such as roots and stems which encloses large air spaces that are created through PCD.
(vii) In the development of unisexual flowers, male and female flowers are present in earlier stages, but only one of these two completes its development while other aborts through PCD.

Photoperiodic induction
1) An appropriate photoperiod in 24 hours cycle constitutes one inductive cycle. Plants may require one or more inductive cycles for flowering.
2) The phenomenon of conversion of leaf primordia into flower primordia under the influence of suitable inductive cycles is called photoperiodic induction.
Example: Xanthium (SDP) - 1 inductive cycle and Plantago (LDP)- 25 inductive cycles.
Site of Photoinductive perception
1) Photoperiodic stimulus is perceived by the leaves.
2) Floral hormone is synthesised in leaves and translocated to the apical tip to promote flowering.
3) This can be explained by a simple experiment on Cocklebur (Xanthium pensylvanicum), a short day plant.
4) Usually Xanthium will flower under short day conditions. If the plant is defoliated and kept under short day conditions it will not flower.
5) Flowering will occur even when all the leaves are removed except one leaf.
6) If a cocklebur plant is defoliated and kept under long day conditions, it will not flower.
7) If one of its leaves is exposed to short day condition and rest are in long day condition, flowering will occur.