Annular thickening rings of thickening laid down on the inner wall of protoxylem vessels and tracheids.

环状加厚：原生木质部导管和管胞的内层环状増厚。

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Annular thickening rings of thickening laid down on the inner wall of protoxylem vessels and tracheids.

环状加厚：原生木质部导管和管胞的内层环状増厚。

youdao