““In his phototropism experiment, he showed that the tip of a shoot sees the light and transfers this information to its midsection to tell it to bend toward the light. Here, Darwin and his son showed that the tip of the root feels the gravity, even though the bending occurs farther up the root. From this Darwin further hypothesized that the root tip somehow sent a signal up the rest of the root to tell it to grow down with the gravity vector.””
