From: Rabbi Mordechai Leib Winkler
To: Rabbi Avraham Tzvi Klein
The responsum clarifies Rashi's statement in Avodah Zarah 74a regarding pomegranates of Dan and nuts of Perech, where what is fit for kil'ei hakerem is considered kil'ei hakerem, and questions how kil'ei hakerem applies to trees.
Source: Yoreh Deah I §199