Long Day Plant (LDP) Some plants require the exposure light for a longer period exceeding a well defined critical duration of light. Among the above given plant LDP are for flowering henbane, Bryophyllum and spinach.

Short Day Plants (SDP) Some plants flower when and these can blossom throughout the year. expos to light for a period less than well defined critical duration of light. e.g., of SDP are. e.g., Xanthium, rice, strawberry.

Day Neutral Plants (DNP) The exposure to light does not affect the flowering in certain plants, e.g., DNP, are sunflower, tomato, maize.

Ethylene is also responsible to play a major roll in determining the sex of monoecious flowers and is associated with the promotions of femaleness in plants thus the farmer must spray ethylene hormone on this cucumber crop to produce female flowers and to increase the yield (number of fruits produced).

(a) IAA Indole acetic acid is the chemical name of auxin. It is synthesised at the growing apices of the plant, e.g., shoot tip, leaf primordia and developing seeds.

(b) Gibberellins It plays an important role in seed germination of plants and is synthesised in the apical shoot buds, young leaves, root tips and developing seeds.

(c) Cytokinins This plays an important role in actively dividing cells and are synthesised mainly in roots, but syntheses also occurs in endosperm of seeds growing embryo and seeds etc.

The apical buds present in tea and other plants prevents the growth of lateral buds in them, by releasing auxin hormone. This phenomenon is called apical dominance, Trimming of tea garden and botanical garden removes the apical bud and allowing the lateral buds to grow laterally and give plants a dense bushy appearance. The scientific explanation for this trimming method is that apical bud is removed thus results in the removal of auxin and phenomenon an of apical dominance is overcomed.

(i) Photosynthesis It is a totally light dependent process. Both quality and quantity affect the rate of the process resulting into total biomass accumulation by plants.

(ii) Transpiration It is loss of water by plant surface. Presence of light increases the temperature, thus affecting the rate of transpiration in plants.

(iii) Flowering The duration of light on plants effects the growth and development of plants, e.g., particularly flowering and this phenomenon is known as photo periodism. On the basis of photoperiodic response day flowering plants are categorised as long day, shert day and day neutral plants.