The Four Species ארבעת המינים

"And you shall take for yourselves on the first day the fruit of a splendid tree, branches of palms, a bough of a leafy tree and willows of the brook"—the Torah does not name the species; the oral tradition identified them: the etrog, the lulav, the myrtle and the willow. They are bound together, and on each day of Sukkot taken up with a blessing—and waved to the four winds, upward and downward: to Him to whom all directions belong (Sukkah 37b).

The Midrash reads the four species as four kinds of people—with taste and fragrance and without—bound into one bundle: the people is whole only when all are in it. Fortunes have been paid for a beautiful etrog in every age. The laws—what renders each unfit—are in tractate Sukkah.