A blossom opens up in sunshine but closes in dark skies and rain, why is this not an example of tropism?

Question

A blossom opens up in sunshine but closes in dark skies and rain, why is this not an example of tropism?

Answer 1

This is a form of nastic movement.  It is a response to external stimuli (light, temp.) but not directed toward the stimuli.  Nastic responses are much faster than tropic usually. Nastic movements like this are reversible and repeatable.

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