anther sac

例句：

1. 1.The pollen grains are enclosed in the anther sac.
   花粉粒被花托囊包裹。
2. 2. During flowering, the anther sac expands to release the pollen.
   开花时，花托囊膨胀释放花粉。
3. 3. The anther sac is a protective structure that helps to prevent the pollen from being washed away by rain.
   花托囊是一种保护结构，有助于防止花粉被雨水冲走。