1. It is found in protoxylem and first metaxylem tracheids and vessels.
可在原生木质部和初始后生木质部的管胞和导管中见到。
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2. Protoxylem the PRIMARY xylem elements that are formed from the procambium first.
初生木质部的成分，最早由原形成层形成。
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3. 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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4. The degree of lignification varies from slight in protoxylem to heavy in sclerenchyma and some xylem vessels, but values of 25-30% lignin and 50% cellulose are average.
5. The degree of lignification varies from slight in protoxylem to heavy in sclerenchyma and some xylem vessels, but values of 25-30% lignin and 50% cellulose are average.
