tro·pism
noun/ˈtrəʊpɪzəm/, /ˈtrɒpɪzəm/
/ˈtrəʊpɪzəm/
[uncountable] (biology)- the action of a living thing turning all or part of itself in a particular direction, towards or away from something such as a source of light
（生物的）向性 Word Originlate 19th cent.: from Greek tropos ‘turning’ (from trepein ‘to turn’) + -ism.