Secondary xylem consists of pitted vessels, parenchyma fibers and rays.

　　次生木質(zhì)部由孔紋導(dǎo)管、薄壁組織及射線所組成。

　　The xylem of ferns and conifers contains only tracheids.

　　蕨類植物和針葉樹的木質(zhì)部僅含有管胞。

　　Large proportion of xylem benefit to the water transfer.

　　葉脈中木質(zhì)部比重越大，越有利于水分的傳輸。

　　A merry Xmas to all our readers!

　　祝廣大讀者圣誕快樂！

　　Merry Xmas!

　　圣誕快樂！