It is thought to act like a valve, sealing the pit when the pressure on the two sides is unequal, e.g. when an adjacent tracheid is damaged.

• 它的作用相当于一个瓣膜，当纹孔两侧的压力不相同时，可以封闭纹孔。例如：当邻近的管胞被破坏就会出现压力相异的情况。