留美老师带你每日说英文 第1063期:为何香草那么珍贵（在线收听）

 　　Vanilla vines take two to four years to fully mature, and their flowers only bloom for one day of the year. In order for the plants to produce beans, they have to be pollinated that day. In most places where vanilla is grown, it isn't a native plant, and there aren't bugs or birds capable of pollinating the flowers.