In the absence of muscle cells, how do plant cells show movements?

Even though plants do not have muscle cells or nervous control, yet they show two types of movements:
(a) Movement in response to stimulus i.e., Nastic movement.
(b) Movement due to growth i.e., Tropic movement. Nastic movements are quick, in response to certain stimulus, for example ‘touch’ in ‘Touch me- not’ plant, reversible, not affected by the direction of the stimulus. Tropic movements on the other hand ate slow, growth related, irreversible and towards or away from the direction of the stimulus, for example, growth of roots towards the earth and growth of shoot towards sun.