What is the meaning of Jalap?

The tubers of the Mexican plant Ipomoea purga (or Exogonium purga), a climber much like the morning-glory. The abstract, extract, and powder, prepared from the tubers, are well known purgative medicines. Other species of Ipomoea yield several inferior kinds of jalap, as the I. Orizabensis, and I. tuberosa.

Source: Webster’s Revised Unabridged Dictionary (1913), via OPTED