xiàngxìng / shì / zhíwù / duì / wàijiè / cìjī / chǎnshēng / de / dìngxiàng / shēngzhǎng / xiànxiàng向性是植物对外界刺激产生的定向生长现象。Tropism is a directional growth phenomenon produced by plants in response to external stimuli.