Vicia faba
Scientists have known that the roots’ receptors for most stimulus are housed in cells of the root cap since Darwin’s 1880 publication of “The power of movement of plants” in which he described his gravitropism experiments. Darwin’s experiments studied "Vicia faba" seedlings. Seedlings were secured in place with pins, the root caps were cauterized, and their growth was observed. Darwin noted that the cauterized root caps did not grow towards any stimulus.