杨树木材主要指次生木质部，是主要的产品器官。
The poplar timber points the secondary xylem mainly, is a main products organ.
次生木质部由孔纹导管、 薄壁组织及射线所组成。
Secondary xylem consists of pitted vessels, parenchyma fibers and rays.
块根的次生木质部发达，导管周围存在额外形成层。
The secondary xylem of root is well developed, and there is supernumerary cambium around the vessels.
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