Developing mature of vascular bundle about 20 days after fertilization.The cells nucleus disappear in this period, secondary wall extended toward the inside.Sieve element formed network.

• 子叶维管束发育成熟约在受精后的20d，成熟时细胞核消失，次生壁向内延伸，筛管分子的细胞壁形成网纹结构。