形成层细胞阶段和伸展生长阶段，POD主要分布在径壁上，尤其是细胞壁角隅处和初生纹孔场附近的细胞壁。
POD was mainly distributed in the radial walls of the cambial cells and expanding xylem cell , especially at the corner of cell wall and cell wall close to the primary pit field .
初生纹孔场