If a short day plant is artificially given long and uninterrupted dark period, it flowers even under long day conditions. Similarly, if a long day plant is artificially given long photoperiods, it flowers even under short day conditions.
Thus, it is possible that a short day plant and a long-day plant growing in the same day of the year by providing suitable photoperiodic conditions artificially.

It is the continuous duration of light, which must not exceeded in short day plants/should be exceeded in long day plants for flowering.

The plants which show no response to light for flowering are called day neutral plants or DNPs.

Leaves are mainly responsible for perception of light intensity in plants. The pigment that receives this stimulates is called phytochrome.

The compound, which can be converted into auxin are called auxin precursors. The compounds, which inhibit the actions of auxins, are termed anti-auxins. The auxins, which can easily be extracted, are called free auxins. And auxins, which are hard to extract and need the use of organic solvents, are reffered to as bound auxins.

Spraying of sugar plants with gibberellin can increases the length of internodes and increased or lengthy internodes will produce more sugar. Thus,gibberelins can increase sugar yield.

Growth in plants is indefinite because they have the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at certain locations. This type of growth is exhibited by roots, stem and their branches and is called an open form of growth.

Plant growth is unique, as plant retain the capacity to grow throughout their life. This ability is due to the presence of meristems. The cells of meristematic tissue have the capacity to divide and self-perpetuate. This form of growth, where new cells are continuously added to the plant body by the activity of meristems, is called open form of growth.

Auxin is required for flowering in pineapple while ethylene is required to initiate flowering and for production of synchronised fruit set in pineapple. Thus, auxin and ethylene can be applied to artificially induce flowering in pineapple plants throughout the year to increase yield.

Zeatin is the growth regulator isolated from endosperm. It controls cell division (cytokinesis) even in non-meristematic tissues

If meristematic cells cease to divide, the growth of the plant will be hindered and will undergo a period of dormancy depending upon the seasonal changes in the climate.

Internal factors that control development in plants are
(i) Genetic factors (intracellular)
(ii) Plant growth regulators (intracellular).

Meristems are the actively dividing cells present in the higher plants like gymnosperms and angiosperms.
These are found in atively growing,regions(like root and shoot of the plant and are responsible for horizontal and vertical growth of the plant.

The symptoms that reflect the occurrence of growth are
(i) permanent increase in size (length and volume).
(ii) increase in fresh weight.

The phenonenon is called apical dominance. Auxin is the phytohormone involved in promoting this phenomenon.

The term short-day plants is actually a misnomer. When photoperiodism was discovered, the duration of the light period was thought to be critical for flowering. However, subsequently researchers found that when the long night period was interrupted in short-day plants, by a brief exposure to light, they failed to flower. In other words, the requirement is actually for a long night or a critical dark period rather than for a short day length. Thus, a short-day plant is more appropriately called as a long-night plant.
Common examples of short-day plants are Xanthium and Chrysanthemum.

Difference between florigen and other plant growth hormones are

Meristems are tissues present in the growing regions of plants.
Primary growth refers to the elongation of stems and roots. All plants exhibit primary growth. Root apical meristem and shoot apical meristem are responsible for the primary growth of the plants and principally contribute to the elongation of the plants along their axis.
The growth that makes plants thicker is called secondary growth.  For example, in dicotyledonous plant and gymnosperms, the lateral meristems, vascular cambium and cork cambium appears later in life. These are the meristems. Their activity in plants to grow in girth (diameter).

Gibberellins are useful in agriculture in the following ways
(i) Application of gibberellins increases the length of the stem and increases the yield of sugar in sugarcane.
(ii) Gibberellins delay senescence and prevent the premature fruits drop.
(iii) It can cause fruits like apple to elongate and improve in shape.

The cell which are derived from root apical meristem and shoot and other meristems undergo certain changes to attain maturity to perform specific functions. This process which leads to maturation of cells is termed as differentiation. During this, the cells undergo a few major structural changes both in their cell walls and protoplasm to perform some specific functions throughout their life.
(i) In plants, some living differentiated cells, e.g. parenchyma can regain the capacity to divided mitotically under certain conditions. A dedifferentiated tissue can act as merisstem, e.g. interfascicular vascular cambium,cork cambium and wound meristem.
(ii) The product of dedifferentiated cells or tissues which lose the ability to divide is called redifferentiated cells and the term is known as redifferentiation. Secondary xylem and secondary phloem from interfascicular vascular cambium, secondary cortex are the examples of tissues.

Plant growth regulators are the chemical molecules secreted by plants affecting the physiological attributes of a plant. There are five main plant growth regulators. These are: Auxins, Gibberellic acid, Cytokinins, Ethylene and Abscisic acid
(i) Auxins
Discovery:
1. The first observations regarding the effects of auxins were made by Charles Darwin and Francis Darwin wherein they saw the coleoptiles of canary gross bending toward a unilateral source of light.
2. It was concluded after a series of experiments that some substance produced at the tip of coleoptiles was responsible for the bending. Finally, this substance was extracted as auxins from the tips of coleoptiles in oat seedlings.
Physiological functions:
1. They control plant cell-growth.
2. They cause the phenomenon of apical dominance.
3. They control division in the vascular cambium and xylem differentiation. - They induce parthenocarpy and prevent abscission of leaves and fruits.
Horticultural applications:
1. They are used as the rooting hormones in stem cuttings.
2. 2-4 D is used weedicide to kill broadleaf, dicotyledonous weeds.
3. They induce parthenocarpy in tomatoes.
4. They promote flowering in pineapple and litchi.
(ii) Gibberellic acid 
Discovery: Bakane or the “foolish rice seedling” disease was first observed by Japanese farmers. In this disease, rice seedlings appear to grow taller than natural plants and become slender and pale green. Later, after several experiments, it was found that this condition was caused by the infection from a certain fungus Gibberella fujikuroi. The active substance was isolated and identified as gibberellic acid.
Physiological functions:
1. It causes elongation of internodes.
2. It promotes bolting in rosette plants.
3. It helps in inducing seed germination by breaking seed dormancy and initiating the synthesis of hydrolases enzymes for digesting reserve food.
Horticultural applications:
1. It helps in increasing the sugar content in sugarcane by increasing the length of the internodes.
2. It increases the length of grape stalks.
3. It improves the shape of an apple.
4. It delays senescence.
5. It hastens maturity and induces seed-production in juvenile conifers.
(iii) Cytokinins
Discovery: Through their experimental observations, F. Skoog and his co-workers found that the tobacco callus differentiated when extracts of vascular tissues, yeast extract, coconut milk, or DNA were added to the culture medium. This led to the discovery of cytokinins.
Physiological functions:
1. They promote the growth of lateral branches by inhibiting apical dominance.
2. They help in the production of new leaves, chloroplasts, and adventitious shoots.
3. They help in delaying senescence by promoting nutrient mobilisation.
Horticultural applications:
1. They are used for preventing apical dominance.
2. They are used for delaying senescence in leaves.
(iv) Ethylene 
Discovery: It was observed that unripe bananas ripened faster when stored with ripe bananas. Later, the substance promoting the ripening was found to be ethylene.
Physiological functions:
1. It helps in breaking seed and bud dormancy.
2. It promotes rapid internode-elongation in deep-water rice plants.
3. It promotes root-growth and formation of root hairs.
4. It promotes senescence and abscission of leaves and flowers.
5. It hastens the respiration rate in fruits and enhances fruit ripening.
Horticultural applications:
1. It is used to initiate flowering and synchronising the fruit set in pineapples.
2. It induces flowering in mango.
3. Ethephon is used to ripen the fruits in tomatoes and apples, and accelerate the abscission of flowers and leaves in cotton, cherry, and walnut.
4. It promotes the number of female flowers in cucumbers.
(v) Abscisic acid 
Discovery: During the mid-1960s, inhibitor-B, abscission II, and dormin were discovered by three independent researchers. These were later on found to be chemically similar and were thereafter called ABA (Abscisic acid).
Physiological functions: 
1. It acts as an inhibitor to plant metabolism.
2. It stimulates stomatal closure during water stress.
3. It induces seed dormancy.
4. It induces abscission of leaves, fruits, and flowers.
Horticultural application: It induces seed dormancy in stored seeds.

The factor which prove the phytohormones act synergistically or antagonsitically are
(i) Cell division is promoted by both auxins and cytokinins acting synergistically.
(ii) Auxins and cytokinins act antagonistically in controlling apical dominance. Auxins cause apical dominance, while cytokinins promotes shoot bud formation.
(iii) Auxins and cytokinins act antagonistically in controlling apical dominance. Auxins cause apical dominance, while cytokinins overcome same.
(iv) Senescence is prevented by auxins and cytokinins,while it is stimulated by absciscis acid.
(v) The activity of cambium and fruit growth seems to be promoted by auxins, gibberellins and cytokinnins, the same is inhibited by abscisic acid.
(vi) The dormancy of seeds and buds is mostly due to abscisic acid and the same is broken by gibberellins.
(vii) Cytokinins cause opening of stomata, while abscisic acid results in their closure.

Plant growth regulators are small, simple molecules secreted in minute quantities, that influence various physiological functions in plants. They are of diverse chemical composition.
(i) Indole compounds [such as-indole-3-Acetic Acid (IAA)]
(ii) Adenine derivatives[such as kinetin, 6-furfuryl amino purine]
(iii) Derivatives of carotenoids {such as Abscisic Acid (ABA)]
(iv) Terpenes[such as gibberellic acids]