葉落知秋　

◎ 葉落知秋 yèluò-zhīqiū

[the falling leaves announce the approach of autumn—revealing signs foretell things to come]見樹葉紛紛落下,就知道秋天到了。比喻從事物發(fā)展的微小變化可以預(yù)測(cè)事物的發(fā)展

落葉知秋,舉一明三。——宋· 普濟(jì)《五燈會(huì)元》