acorn tube

例句：

1. 1.The acorn tube is a unique structure found in some species of trees.
   松果管是某些树种中特有的结构。
2. 2.The acorn tube is used to transport seeds from the tree to the ground.
   松果管用于将种子从树上运输到地面。
3. 3.The acorn tube is an important part of the plant's life cycle.
   松果管是植物生命周期中的重要部分。