What is cardamom? It is a perennial plant that blooms in late spring and early summer. At first, the tender leaves are rolled, the leaves are gradually unfolded and the flowers are gradually opened. February is the budding period, which is often used to describe the innocent and dreamy age of girls in literary works. This sentence is from Du Mu's poem "Farewell": "Cardamom blooms more than thirteen times, and cardamom blooms in early February. It is better to roll up the bead curtain when the spring breeze is ten miles along Yangzhou Road. " When Du Mu was in his thirties, he was "down and out in Yangzhou". Sometimes he traveled and was bored. He wrote this poem as a gift to a young prostitute. The "thirteen wonders" in the poem are clearly identified as girls of thirteen or fourteen, just like cardamom in bud. This metaphor is very accurate and vivid.