| Answer | As plants are fixed to the ground, they cannot move bodily
but their protoplasm is sensitive to certain external
factors act as stimuli such as heat, light, gravity,
chemicals, electricity etc.
Movements may be classified into two main groups.
1. Autonomic or Spontaneous.
2. Paratonic or Induced.
Spontaneous Movements. It is the movements of creation
organs of plants without the influence of any external
stimuli e.g. movement of protoplasm and cilia, brisk
movement of many desmids movement of protoplasm and cilia,
brisk movement of many desmids etc..
This type of movements may be of two kinds.
(a)Movement of variation:- These movement are due to
variation in turgity of cell. This movement is exhibited by
pulsation.
This kind of movement is seen in Indian telegraph plant.
(b)Movement of growth:- This si movement of growing regions
die to unequal growth of organs on different sides. This
kind is seen in some creepers and trailers and this type of
movement is very slow.
Induced Movement:-This is movement of plant organ are
induced by some external stimuls. These induced movements
are of following kinds
(a)taxes
(b)tropisms
(c)nasties
(a)Taxes:-Taxic movements are the movements of free organs
or entire free organism induced by external sources at
temperature light and chemical substance. Cillated bodies as
Zoospores and antherozoids show this kind of movement. These
bodies either show positive or negative movement by the
stimulus.
(b)Tropism:- In this type of movement the organ concerned
moves either towards the source of the stimulus or away from
it. These movements are also influenced by external stimulus
as contact gravity and moisture. These movements are of
following kinds according to nature of stimulus.
(c)Haptotropism:-This moment is induced by contact with
foreign body. Climbers, Tendils and twinning stems show
this kind of movement, when climbers or tendrils some in
contact with any support, the opposite side of contact
continues to grow while the growth of contacted side is
checked. This opposite side continues to grow while the
growth of contacted side is checked. This opposite side
continue to grow until it coil around the object. Some
climbers climb clockwise some move anticlockwise.
(d)Phototropism:- These movements of plant organs are due to
influence of light. Some organs of plants are attracted by
light and grow towards it as shoots. These are positively
heliotropic or positively phototropic but some orgems e.g.
roots grow away form light are known to be negatively
phototropic or negatively heliotropic. Dorsiventral leaves
are said to be Diaheliotropic these grow at tight angles
to the direction of light so their upper surface is only
exposed to light.
(e) Geotropism:-This kind of plant movement is due to
influence of forced gravity. The roots shows positive
geotropism but stem show negative geotropism.
(f)Moisture:-This movement of plant organs is due to
moisture and is known as hydrotropism. Roots show a great
tendency to grow towards the source of moisture and these
are therefore known as positively hydrotropism.
(g)Nasties or Nastic Movements:- Nasties or nastic movements
are movements dorsiventral or like petals, leaves induced by
external stimuli as contact light, and temperature. These
movements not like tropic movements, as in these directions
of movements is not determined by direction of stimulus.
Two the of movements are found under these which are as follows
(h)Scismonasty:-This type of movement is so called as this
is brought about by some mechanical stimuli as contact with
a foreign body; drops of rain etc.
Examples of plants which show this kind of movements are
sensitive plant, Neptunia
Nyctinasty:-This type of movement is due to alternation of
day and night i.e. light and darkness. Leaves are mostly
affected by this kind of movement. Lequminous plants show
this kind of movements..
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