http://www.cls.zju.edu.cn/sub/fulab/plant_Antomy/plant/vtphloem/conifer3/01n.html

http://sols.unlv.edu/Schulte/Anatomy/Stems/PinusStemHi.jpg

http://sols.unlv.edu/Schulte/Anatomy/Secondary/Secondary.html

http://www2.puc.edu/Faculty/Gilbert_Muth/botglosx.htm

http://botit.botany.wisc.edu/Anatomy/Glossary/Xylem.html

http://www.doctortee.com/dsu/tiftickjian/plant-anat/xylem.html

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