(i) Auxin fails to cause growth of intact plants because the required amount of auxin is already present in such plants and they do not need external supply of auxins.
(ii) Vitamins have no specific influence on growth of plants. They are essential dietary factors needed by an organism in small amounts. They influence on growth and metabolism through direct nutritive effects.
(iii) Short day plants need long and uninterrupted dark period for flowering. Therefore, it is appropriate to call a short-day plant, a long-night plant.
(iv) Plants belonging to halophytes and growing in marshy lands face a great difficulty in seed germination due to presence of high concentration of salt in water. These plants solve this problem by vivipary.
(v) Gibberellins require the presence of meristematic cells to cause elongation growth. Therefore,
they do not enhance growth of isolated plant parts if meristematic cells are absent.