Demai, Chapter 6, Mishnah 4. This mishnah deals with the question of who owns the Terumah and tithes in a field received as a sharecropping arrangement when the owner of the field is a kohen or a Levi, and also with the law of Maaser Sheni in a field received from a Jerusalemite householder.
A Yisrael who received a field from a kohen or a Levi:
An ordinary Yisrael who receives a field as a sharecropper for a percentage from a kohen or a Levi - "HaMaasros LaBealim" - the tithes belong to the owner of the field. Unlike the previous mishnah, where the owner of the field was an ordinary Yisrael and the Tannaim disagreed about the case where the kohen or the Levi was the sharecropper, here, where the owner of the field is a kohen or a Levi, everyone agrees that all the Terumah and tithes - even the percentage belonging to the sharecropper - go to the owner of the field. The reason: since I am the owner of the field, I expected all the tithes to be given to me, and that expectation was part of the understanding of the deal.
The dispute between Rabbi Shemayah and the Sages regarding Maaser Sheni:
Rabbi Shemayah comes to teach a new law in an additional case, concerning Maaser Sheni, which is eaten in Jerusalem. He says: "HaKartani SheKibel Sadeh MiYerushalmi - Maaser Sheni Shelo LaYerushalmi" - a villager who received a field from a Jerusalemite gives his Maaser Sheni to the Jerusalemite. A "kartani" is someone who lives in a town or village outside Jerusalem, that is, someone who is not a resident of Jerusalem. If a villager sharecropper received a field for a percentage from a Jerusalemite householder, all the Maaser Sheni of that field is handed over to the Jerusalemite householder, including the sharecropper's own portion, for since the owner lives in Jerusalem, that is the understanding between the parties.
The Sages disagree and say: "Rashai Hu HaKartani LaAlos VeLeEchol BiYerushalayim" - the villager is entitled to go up and eat in Jerusalem. In their view there is no special distinction or special status for someone who lives in Jerusalem; it simply happens that he lives there, and perhaps it is more convenient for him. The villager who lives outside Jerusalem can just as well go up and eat those same foods in Jerusalem, and the Jerusalemite is not like a kohen or a Levi who have rights in the matter. Therefore, with Maaser Sheni each one receives his own portion:
The percentage of the Maaser Sheni produce that belongs to the householder - goes to the householder.
The percentage that belongs to the sharecropper - goes to the sharecropper.
And each of them can eat his portion in Jerusalem.
In summary: in this mishnah we learned two laws. First: a Yisrael who received a field as a sharecropper from a kohen or a Levi - all the tithes go to the owner of the field, and about this there is no dispute, since that was the understanding of the deal. Second: the dispute between Rabbi Shemayah and the Sages about a villager who received a field from a Jerusalemite - according to Rabbi Shemayah all the Maaser Sheni goes to the Jerusalemite, while according to the Sages a resident of Jerusalem has no special status, and the villager is entitled to go up and eat his own portion in Jerusalem.