Short answers, pulled from the story.
The sharp flavor of a radish is created by allyl isothiocyanates, which form when glucosinolate and the enzyme myrosinase combine after the plant tissue is damaged. This reaction occurs when a person bites into a raw radish, triggering a complex chemical defense mechanism originally designed to deter insects and herbivores.
Scientists have tentatively located the birthplace of the radish in Southeast Asia, the only region where truly wild forms of the plant have been discovered. The plant entered the historical record in ancient times, with Greek and Roman agriculturalists of the first century documenting small, large, round, long, mild, and sharp varieties.
Radish seeds germinate in three to four days in moist conditions with soil temperatures between 45 and 85 degrees Fahrenheit. Under average conditions, the crop matures in three to four weeks, but in colder weather, six to seven weeks may be required.
Radish root skin color ranges from white through pink, red, purple, yellow, and green to black, with the flesh usually being white. Smaller types have round roots up to 3 inches in diameter, while longer forms like oriental radishes and daikon grow up to 24 inches long.
Citizens of Oaxaca, Mexico, celebrate the Night of the Radishes on December 23 as a part of Christmas celebrations. This folk art competition uses a large type of radish up to 12 inches long and weighing up to 5 pounds to carve religious and popular figures.
Radishes can be useful as companion plants because their pungent odor deters insect pests such as aphids, cucumber beetles, tomato hornworms, squash bugs, and ants. They can also function as a trap crop, luring insect pests away from the main crop while cucumbers and radishes thrive when grown in close association.