主根,直根
Taproot \Tap"root`\, n. (Bot.) The root of a plant which penetrates the earth directly downward to a considerable depth without dividing.
taproot
n 1: (botany) main root of a plant growing straight downward from
the stem
2: something that provides an important central source for
growth or development; "the taproot of his resentment";
"genius and insanity spring from the same taproot"