这样的加厚允许木质部在环间沿展，当周围组织生长时，不会破裂。
Such thickening allows extension of the XYLEM between the rings so that it is not ruptured as the surrounding tissues grow.
结果表明，不同杨树品系间韧皮部单宁含量差异极显著，木质部单宁含量差异不显著；杨树各品系的单宁含量与杨树的被害株率关系不紧密。
Results showed that a significant difference in tannin content was found in phloem of different poplar strains, while the difference in xylem was not obvious.
木质部aba与土壤干旱胁迫间的关系类似于根系aba的变化，但低氮与高氮处理木质部aba含量的差异没有根系aba的显著。
Similar trend was showed with the xylem SAP ABA, but no difference was observed in xylem ABA in response to soil drying between different nitrogen treatments.
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