韧皮部

例句：

1. 1. The tree's trunk is the vascular systemof the plant.
   树的树干是植物的维管系统。
2. 2. The roots are thevascular system of the plant.
   根是植物的维管系统。
3. 3. Thebark is the outer layerof the tree, protecting thewood from damage.
   树皮是树的外层，保护木材免受损害。