Sugarbeet is a long day plant. It is because in this plant flowering takes place when the plants are exposed to day length longer than a critical photoperiod.

(i) Photoperiodism
(ii) Phototropism
(iii) Photosynthesis

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.

The rice seedlings infected with fungus Gibberella fujikuroi is called foolish seedlings because these seedlings grow foolishly. i.e. there is abnormal increase in internodal area of rice and ultimately.so tall that they ultimately, fall on ground and result into death of plants.

Meristematic cells are actively dividing cells which show mitotic divisions, ie.each chromosome is split lengthwise into two homologous chromatids, which pass equally into daughter cells. These possess thin cell wasll and a dense cytoplasm.
Mature cells are incapable of divisions becauses inthese cells differentiation has take place. Also mature cells do not possess thin cell wall in and a dense cytoplasm.

Hence, shoot would develop first from the callus.

2,4-D is selective her bicide (weed killer), spray of 2, 4-D is used to kill plants with broad leaved weeds.

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.

Ranuculus flabellaris.

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

(i) Some plants require a periodic exposure to alternate light and dark period for its flowering response and this phenomenon is called photoperiodism.
(ii) The requirement of light exposure is critical. the SDP plants when exposed to light period in excess of critical period fail to flower.
(iii) Those plants, which require exposure to light period at critical or more than critical period for its flowering response are called long-day plants.
(iv) Nicotiana tobacum fails to flower if exposed to more than the critical period of light because it is a short-day plant.

Difference between florigen and other plant growth hormones are

Plants growth is a unique phenomenon because plants retain the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at certain locations in their body. The cells of meristems have the capacity to divide and self-perpetuate.
The cells thus produced, however, soon loses the capacity to divide and such cells make up the plant body. This form of growth wherein new cells are always being added to the plant body by the activity of the meristem is called the open form of growth. Yes,this statement holds true for sponges also.

Anyone parameter is not good enough to demonstrate grown throughout the life of a flowering plant because the plants exhibit different types of growth during different stages of their life cycle.
In the seedling stage, they are in state of active mitotic cell divisions, then they undergo active cell enlargement stage during growing stage. After the formation of various organs, they undergo cell differentiation or get matured. Finally in the reproductive or flowering stage of their life cycle, they exhibit reductional divisions.

(a) Arithmetic Growth. In arithmetic growth, following mitotic cell division, only one daughter cell continues to divide while the other differentiates and matures. The simplest expression of arithmetic growth is exemplified by a root elongating at a constant rate.
Mathematically, it is expressed as
L_t = L₀ + rt
L_t = length at time 't'
L₀= length at time 'zero'
r = growth rate/elongation per unit time

(b) Geometric Growth. In most systems, the initial growth is slow (lag phase), and it increases rapidly thereafter - at an exponential rate (log or exponential phase). Here, both the progeny cells following mitotic cell division retain the ability to divide and continue to do so. However, with limited nutrient supply, the growth slows down leading to a stationary phase. If we plot the parameter of growth against time, we get a typical sigmoid or S-curve. A sigmoid curve is a characteristic of living organism growing in a natural environment. It is typical for all cells, tissues and organs of a plant.

The exponential growth can be expressed as
W₁ = W_o ert
W₁ = final size (weight, height, number etc.)
W₀= initial size at the beginning of the period
r = growth rate
t = time of growth
e = base of natural logarithms
Here, r is the relative growth rate and is also the measure of the ability of the plant to produce new plant material, referred to as efficiency index. Hence, the
final size of WI depends on the initial size, W₀.
Quantitative comparisons between the growth of living system can also be made in two ways:
(i) measurement and the comparison of total growth per unit time is called the absolute growth rate.
(ii) The growth of the given system per unit time expressed on a common basis,
e.g., per unit initial parameter is called the relative growth rate.
(c) Sigmoid growth curve
The growth of living organisms in their natural environment is characterised by an S-shaped curve called sigmoid growth curve. This curve is divided into three phases – lag phase, log phase or exponential phase of rapid growth, and stationary phase. 
  
Exponential growth can be expressed as:
W₁ = W₀eⁿ
Where,
W₁ = Final size
W₀ = Initial size
r = Growth rate
t = Time of growth
e = Base of natural logarithms
(d) Absolute and Relative growth rates:
1. Absolute growth rate is total growth per unit time. In the given representation, the absolute growth rate for both leaves is 5 square centimeters per given time.
2. Relative growth is the rate of growth with respect to the initial size. Here, the relative growth rate for leaf A is higher as its surface area increased by 100% while the surface area of leaf B increased by only 10%.

Growth. Growth can be defined as an irreversible permanent increase in size of an organ or its parts or even of an individual cell. Generally, growth is accompanied by metabolic processes (both anabolic and catabolic), that occur at the expense of energy.
Differentiation. The cells derived from root apical and shoot-apical meristems and cambium differentiate and mature to perform specific functions. This act leading to maturation is termed as differentiation. During differentiation, cells undergo few to major structural changes both in their cell walls and protoplasm. For example, to form a tracheary element, the cells would lose their protoplasm. They also develops a very strong, elastic, lignocellulosic secondary cell walls, to carry water to long distances even under extreme tension.
Development. Development is a term that includes all changes that an organism goes through during its life cycle from germination of the seed to senescence.
Dedifferentiation. The living differentiated cells, that by now have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation. For example, formation of meristems - interfascicular cambium and cork cambium from fully differentiated parenchyma cells.
Redifferentiation. While undergoing dedifferentiation plant cells once again lose their capacity to divide and become mature. This process is called redifferentiation.
Determinate Growth. Although growth in most of the plant parts is unlimited. Certain parts grow up to a certain level and then stop growing. This kind of growth is called determinate growth.
Growth Rate. The increased growth per unit time is termed as growth rate. Thus, rate of growth can be expressed, mathematically. An organism, or a part of the organism can produce more cells in a variety of ways. The growth rate shows an increase that may be arithmetic or geometrical. Quantitative comparisons between the growth of living system can also be made in two ways:
(i) measurement and the comparison of total growth per unit time is called the absolute growth rate.
(ii) The growth of the given system per unit time expressed on a common basis,
e.g., per unit initial parameter is called the relative growth rate.

Growth is defined as a permanent or irreversible increase in dry weight, mass or volume of cell, organ or organisms.
Plant growth takes place in three steps or phase-cell division, cell elongation and cell maturation.
(i) Cell Division Phase
It is also called formative phase.
(i) New cells are produced by mitotic divisions of the pre-existing cells.
(ii) The meristematic cells have thin cellulose walls with abundant plasmodesmata connections, dense protoplasm and conspicuous nuclei.
(iii) In higher plants, cell division occurs in meristems or growing points.
(iv) As the formation of new cells requires intense biosynthetic activity, the rate of respiration in the cells of formation phase is very high.
(ii) Cell Enlargement Phase
(i) It is also called phase of cell elongation.
(ii) This phase lies just behind the growing points and is mainly responsible for growth of plant parts.
(iii) The newly formed cells, produced in formative phase undergo enlargement.
(iv) The cell walls of the enlarging of cell show plastic extension through, enzymatic loosening of microfibrils and deposition of new materials.
(v) The enlarging cell also develops a central vacuole, rate of respiration is high but less than that of the cells in the formative phase.
(v) Thus, this phase is characterised by cell enlargement, new cellwall deposition and increased vacuolation
(iii) Cell Maturation Phase
(i) This phase occurs just behind the phase of elongation.
(ii) The enlarged cells develop into particular type of cells by undergoing structural and physiological differentiation.
(iii) Hence, at this phase all the diverse tissue types observed in root or stem.

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.