seminal root system种子根系
lateral seminal root次生胚根
first seminal root主胚根
The diameter of later xylem vessel of the seminal root and first pair of primary roots were greater than these of second and third pairs.
2．种子根和第一对主根的后生导管直径大于第二对、第三对主根。
参考来源 - 小麦苗期根的分枝规律与解剖结构