额外根的英文

• extraneous root
• supernumerary root

• 额外:    extra; additional; added
• 根:    root
• 外根鞘:    external root sheach; external root sheath; outer root sheath; outer root-sheath
• 额外:    (超出规定数量或范围的) extra; additional; added 做额外工作 do extra work; 旅馆每个房间都有电视机作为额外优待。 television is available in each of the hotel rooms as an extra
• 毛外根鞘:    external root sheath