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The answer is (a) Borthwick and Hendricks

Ethaphone (2-Chloro ethyl phosphoric acid).

The answer is (a) Auxin

The total time period during which maximum growth takes place for completing all the phases of growth is called a grand period of growth

The answer is (b) Florigen

The answer is (d) 2 – 4D

The answer is (a) Auxin

1. Gibberellins: 

• Gibberellins were discovered in Japan and the discovery is related to a disease in Rice (Paddy) plant.
• In 1890 a disease occurred in the Rice fields in japan where some Rice plants grew extraordinary tall and remained flowerless.
• This disease was named as “Bakanae disease” (In Japanese language Bakanae means foolish) Hori (1898) Studied this disease in detail and found that these plants were infected with a fungus Gibberella fuji-Kuro (perfect state of an imperfect fungus Fusarium moniliform).
• The infected seedlings grew extra tall, and thin and do not bear flowers, fruits and seeds. So these were called “foolish seedling” and the disease as a foolish seedling disease.
• Kurosawa (1926) proved that secretion by the fungus sprayed on the healthy plant results in this disease.
• Yobuta and Hayashi (1939), isolated the substance in pure crystalline form from the culture filtrate of Gibberella fuji-Kuro and named it Gibberellin.
• Brian et. al (1954) isolated pure form of single gibberellin and named if Gibberellic acid.
• About 100 different gibberellins have been obtained from different fungi and higher plants. These are known as GA₁, GA₂, GA₃, G₄……… GA100. Among this GA3 is the first discovered and commonly found gibberellin. 

2. Cytokinins: 

• G Haberland (1913) First observed that in the phloem of some plants, some substances are found which stimulate cell division. 
• J. Van Overbeek (1941) showed that there are certain substances in coconut milk which promote cell division. 
• Skoog and Miller (1955) isolated a very useful substance from DNA of yeast which promotes cell division and named it as kinetin. 
• Letham (1963) named Kinetin as Cytokinin. 
• Letham and Miller (1964) isolated a substance, similar to cytokinin, from the endosperm, of maize and called it Zeatin.
  Zeatin is the first naturally occurring cytokinin. 

3. Growth inhibitor substance: 

• Those hormones or substances which inhibit the rate of growth are called growth inhibitors. 
• These substances are required for controlling and balancing growth and development. 
• Abscisic acid is the most important growth-inhibiting hormone.

4. Abscisic Acid (ABA): 

• This is the most important naturally occurring growth inhibitor found in plants.
• It helps the plant to successfully survive adverse environmental conditions.
• Hence it is also called stress hormone.
• Wareing (1963) isolated one growth-inhibiting substance from the leaves of Acer plant and named it as Dormin.
• Addicott et. al. (1963) isolated one substance from the floral buds of cotton and named it as Abscisin.
• Later on, it was proved that domain and abscision are the same substance and these were named as Abscisic Acid (ABA).

5. Abscission: 

• Shedding of leaves, flowers and fruits from the mother plant by a natural process is called abscission.
• It is a biological process which is initiated due to changes in the cells of the basal portion of the parts which fall off. 
• The middle lamella and the cell wall of the cells in the basal portion are digested by pectinase and cellulase enzymes. 
• As a result of breaking of middle lamella and cell-wall, cells in a definite region begin to separate from each other. 
• The tissues in this area become weak and soft and a layer is formed which is called an abscission layer. 
• The cells situated just below the abscission layer become meristematic and form cork cells.
• This cork forms a protective layer or abscission zone.
• Due to strong wind or rain, the plant part separates from the region of abscission and fall off. 
• Abscission is due to a change in the hormonal balance. Abscisic acid plays a major role in the process of abscission. 

6 Vernalization:

• In the majority of plants, besides photoperiod temperature also has an important role in growth and development. 
• The response of plants towards temperature relating to growth and development was first observed by a Russian scientist Lysenko (1928) while working on winter and spring varieties of rice. 
• In annual plants, light has a major effect on flowering and the effect of temperature is secondary. 
• In biennial plants the situation is different. In these plants, there is only vegetative growth in the first year and flowering is completed in the second year. 
• Before flowering cold temperature exposure of winter is necessary for these plants, and in absence of cold treatment reproductive stage does not begin and they remain in the vegetative stage. 
• The method of inducing flowering by chilling (cold) treatment is called vernalization. 
• According to Choird (1960), vernalization can be defined as “Inducing ability of flowering by chilling treatment artificially is called vernalization”

Auxin word originated from the Greek word Auxin which means “To grow” or increase in growth. Presently auxin term represents the group of plant hormones which promote the growth of stem or coleoptile. Indole Acetic Acid (IAA) and those naturally occurring and artificially synthesized products which have some properties as IAA are termed as Auxins. 

Physiological Effects of Auxins on Plant growth are as follows: 

1. Apical dominance. 

2. Cell elongation. 

3. Root initiation. 

4. Parthenocarpy. 

5. Prevention of lodging. 

6. Control of dormancy. 

7. Thinning of flowers. 

8. Effect on abscission. 

9. Eradication of weeds.

10. Shortening of Internodes.

11. Tissue Culture. 

1. Apical Dominance:

• It is commonly observed that if the apical bud remains intact and growing, the lateral buds remain suppressed. This is called apical dominance. 
• Removal of apical bud causes fast growth of lateral buds, and the plant becomes bush-like. 
• It is because of this the hedge is regularly cut and trimmed to remove apical buds so that it becomes dense. 

2.Cell Elongation: 

• The main function of auxin is to induce elongation of the cells which are formed by division of cells of the apical meristem. 
• The high concentration of auxin in apical region promotes cell elongation.
• Because of this, the shoot apex is negatively geotropic and positively phototropic. 

3. Root Initiation: 

• Auxins promote the initiation of adventitious roots from the nodes or basal region of stem. 
• Plant growers use BA and NAA to induce root formation in the stem
• Auxins promote root growth at extremely low concentration (i.e. 10–7 to 10–13 M concentration).
• If the lower end of stem cutting is dipped in auxin and then planted, roots are rapidly developed. Example: Rose, Bougainvillea, Citrus, etc. 

4. Parthenocarpy: 

• The process of development of ovary into the fruit without fertilization is called parthenocarpy. 
• Fruits formed by parthenocarpy are called parthenocarpic or seedless fruits. 
• For inducing parthenocarpy, the stamens are removed in the bud stage and auxin is sprayed on the stigma
• Seedless fruits are developed by external application of auxin in tomatoes, apples, cucumbers, orange, lemon, brinjal and grapes etc.

5. Prevention of Lodging: 

• In many crop plants such as wheat, the thin and weak stem bends near the base due to strong winds and falls on the ground. This is called lodging.
• If the solution of auxin is sprayed on small young plants, the basal portion of the plants become strong and chances of falling in the strong wind are reduced.
• Hence use of auxin prevents lodging.

 6. Control of Dormancy: 

• Auxin maintains dormancy in seed and vegetative propagules (Rhizome etc.).
• Auxin prevents germination of seeds and sprouting of buds so that these can be stored for a long duration.
• Potato tubers sprayed with NAA can be stored for about three (3) years.

• In some plants, growth of lateral and axillary buds remain suppressed partially or completely under the influence of the apical bud. This effect of apical bud is called as apical dominance.
• In such cases, when the apical bud is removed the lateral and the axillary buds become active and begin to grow and the plant becomes bushy

The answer is (b) Auxin

By cutting of apical bud, the lateral and axillary buds become active and on account of this, the bush becomes dense. Hence to discourage apical growth and promote the growth of lateral buds, the top of the hedge is trimmed.

Kinetin is 6- furfuryl amino purine.

• NAA (Naphthalene Acetic Acid).
• IBA (Indole -3 Butyric Acid).