Demai, Chapter Five, Mishnah Ten
This mishnah deals with giving terumah and tithes for produce grown in two different kinds of pots: perforated and non-perforated. The question is: is the pot considered to be like land?
1) A perforated pot is considered like land.
2) If one gave terumah from [produce grown in] the soil for [produce grown in] a perforated pot, or from [produce grown in] a perforated pot for [produce grown in] the soil, his terumah is terumah.
3) [If he gave terumah] from [produce grown in] a pot that was not perforated for [produce grown in] a pot that was perforated, [it is] terumah, but he must go back and give terumah again.
4) [If he gave terumah] from [produce grown in] a perforated pot for [produce grown in] a pot which was not perforated, [it is] terumah, but it may not be eaten until he first gives terumah and tithes for it.
Section one: A plant that grows in a perforated pot is considered as if it grew directly from the land. Since the pot is resting on land and through the hole in its bottom the plant can send its roots out to the ground, it is considered as land. The halakhic consequence of this is that the produce that grows in it is obligated from the Torah for terumah and tithes. In contrast, one is only obligated derabbanan (from rabbinic law) to separate terumah and tithes from produce grown in a non-perforated pot. This principle guides the following three clauses.
Section two: Since plants grown in perforated pots are treated as if they grew directly from the land, if one gave terumah for something that grows in such a pot in order to exempt other produce that grows directly from the land or vice versa, that which he separates is terumah. This is effective means to exempt the produce from being liable for terumah. In other words, this is perfectly fine.
Section three: In this case he gave terumah from a non-perforated pot (only liable for terumah from rabbinic law) for produce grown in a pot that was not perforated (liable from toraitic law). The produce that he called terumah is terumah because once someone calls something terumah it generally cannot go back to being non-sacred produce. However, he has not yet successfully separated tithes from the produce that grew from the perforated pot. Before he eats this produce, he must go back and separate terumah again.
Section four: This is the opposite scenariohe separates terumah from a perforated pot for produce from a non-perforated pot. Again, that which he calls terumah is terumah. However, this terumah cannot be eaten until tithes and terumah have been separated for it. The reason is that this terumah was taken from something liable in order to exempt something not liable (the non-perforated pot) and not to exempt that which was in the perforated pot. That which he calls terumah is therefore, technically still untithed produce (tevel), which no one, including priests, can eat until terumah and tithes have been separated.