What makes the movement of plants is discussed in this chapter.
Conditions necessary for Plant Movements
1. Water : Proper water supply is essential for certain kind of movements.
2. Temperature : Movement of plants can take place within a certain range of temperature only.
3. Oxygen : The energy produced during respiration due to oxygen, makes the plants move.
4. Hormones : Plant hormones like auxins, specially indole acetic acid (IAA), are responsible for certain kind of movements like phototropism, geotropism, etc.
(a) With the help of cilia: e.g. Volvox, Chlamydomonas.
(b) Movement of Protoplasm : It is of three kinds of movements; such as, cyclosis, amoeboid and ciliary.
Rotation : The movement of protoplasm within the cell without changing its direction is called rotation. Examples—This type of movement is seen in the leaves of Vallisneria, Chara, etc.
Circulation : The irregular movement of protoplasm within the cell changing its direction is called circulation. Examples—It is seen in the stamen hairs of Rheo, Tradescantia, etc.
Examples—This type of movement of protoplast is also common in Myxomycetes.
Examples—The zoospores of certain thallophytes (algae and fungi) and the antherozoids of moss, fern, etc. show ciliary movement.
Example—Movement of algae, bacteria, etc. towards weak light.
Example—In mosses cane sugar is secreted by the archegonium to induce movement of the antherozoids toward it and in ferns malic acid is secreted similarly to attract the antherozoids.
Examples—Movement of protoplasm at a higher rate within the cell due to rise in temperature (upto a certain limit) only.
The shoots grow towards the source of light and they are said to be positively phototropic, while the roots grow away from it and are called negatively phototropic. Whereas the leaves remain at right angles to the source of light and are said to be transversely phtotropic. Evidence : A plant kept near an open window bends towards the source of light.
Examples—Flowers like water-lily, sunflower, poppy, etc. open at sunrise and close at sunset and are positively photonastic. Flowers of night queen (Cestrum nocturnum) open at night and are called negatively photonastic. These movements occur due to change in turgidity. The most striking photonastic movement is the sleep movement of leaves exhibited by Oxalis, Cloves, etc. During the day time the leaves of those plants expand horizontally. It starts dropping and closing towards the evening and do not regain its normal condition until the next morning.
Examples—Flowers like Tulip, Crocus, open at higher temperature but close as the temperature falls. Such a movement is also caused by change in turgidity.
Example—Movement of tendril away from chloroform and curving of tentacles of Sundew (insectivorous plant) in response to soluble proteins when placed at the centre of the leaf.
Example—Leave of Acacia, Bauhinia, Marsilea, etc. The leaves of Oxalis open during day but closes at night. The opening and closing of cactus, tobacco flowers are also induced by both light intensity and temperature.
Example—When the leaflets of the sensitive plant touch me not or mimosa pudica is touched, they droop down. The mechanism of movement is based on changes in turgor pressure.
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