The "citrons" that are shipped from Palestine to Ireland are one of the original citrus fruits, ancestors of modern-day lemons, limes, oranges, grapefruits, and other products of hybridization. They play an important role in the Jewish Sukkot ritual, as Bloom thinks when he remembers Moisel saying, "Must be without a flaw."

JH 2017

Citron fruits on the tree. Source: Wikimedia Commons.

The lulav, a silver box for carrying the etrog, and the fruit itself. Source: Wikimedia Commons.