Maseches Demai, Chapter 6, Mishnah 1. This mishnah discusses two types of tenant farmers, and the question of whether the tenant, at the time he gives the landowner his share, is obligated to separate Terumah and maaser from what he hands over.
The two types of arrangements:
Mekabel - one who takes on the field as a tenant and agrees with the landowner to give him a percentage of the produce and the crop. This is ordinary tenant farming, based on a division by percentages.
Choker - one who makes an arrangement that is not based on percentages, but on a fixed payment set in advance: a specified number of se'ah that he commits to give the landowner.
"HaMekabel sadeh miYisrael, min ha'oved kochavim umin haKuti - yachalok lifneihem":
The mishnah opens with the case of a mekabel, that is, tenancy based on percentages, whether he received the field from a Jew, from a non-Jew, or from a Kuti. In all of these, "yachalok lifneihem" - he may divide the produce in their presence and give them their share without separating maaser beforehand, and it is they who will need to separate the maaser.
It is worth noting that the commentators disagree about the status of the Terumah. We will follow the view of the Chiddushei Maharich, who holds that even in the first case in the mishnah there is an obligation to separate Terumah. The reason: with Terumah, from the moment they begin to break open the pile of grain and thresh it, the Terumah must be separated at that very moment, and there is no option to postpone the separation to a later time. The Terumah is therefore separated immediately when the grain pile is opened up, whereas the obligation to separate maaser does not rest upon him.
By strict law it should have been the case that even before paying the landowner, and even from the percentage due to him, the tenant would separate maaser, since anything that leaves a person's possession and is handed to someone else - including the landowner - requires that maaser be separated first. However, the Sages established an exception here for the sake of settling Eretz Yisrael: they wanted to ensure that Eretz Yisrael would be settled, and they were concerned that people would refrain from working fields as tenants so as not to have to deal with separating maaser and giving it. So that people would be willing to enter into arrangements of this kind, the Sages permitted the maaser to be separated by the landowner rather than by the tenant.
"HaChoker sadeh miYisrael - torem venosen lo":
From here the mishnah moves to the law of the choker, who gives the owner of the field a fixed payment of a set number of se'ah determined in advance, not according to percentages. Regarding one who rents a field from a Jew - "torem venosen lo": he must separate the Terumah, as we mentioned in the first clause according to the Chiddushei Maharich, but he is not obligated to separate maaser. This law stands in contrast to the law of the next mishnah, where we will see that one who rents a field from a non-Jew is obligated to separate maaser as well.
The words of Rabbi Yehudah:
On this Rabbi Yehudah says: "Eimasai? Bizman shenasan lo me'osah hasadeh ume'oso hamin" - the exemption from maaser applies specifically when he pays from the field about which the arrangement was made and from the type of produce about which the arrangement was made. "Aval im nasan lo misadeh acheres o mimin acher - me'aser venosen lo" - if he comes to pay his debt with produce from a different field or of a different type, he must separate maaser first, before he gives it to him.
The reason for the distinction: when he pays with produce that is not from the field and the type that were stipulated, he is relating to the produce as cash, and anyone who uses produce as cash to pay off his debt must separate maaser before it leaves his hands. Only when he gives him from the very produce that he rented the field to grow, from the items to which the landowner has an actual claim, is he not required to separate the maaser in advance, and he may leave it to the landowner to separate it.
In summary: in this mishnah we learned the distinction between a mekabel and a choker. The mekabel, who works the land for a percentage, "yachalok lifneihem" - and he is not obligated to separate maaser, because of the enactment of the Sages for the sake of settling Eretz Yisrael, while the Terumah is separated immediately when the grain pile is opened up. The choker who rents from a Jew "torem venosen lo" and is exempt from maaser, and Rabbi Yehudah defines that this exemption applies specifically when he pays from that same field and that same type of produce, but when he pays from a different field or a different type, this is like paying off his debt in cash, and he separates maaser and then gives it to him.
In the next mishnah we will deal with the law of one who rents a field from a non-Jew, and we will see that there the obligation to separate maaser does apply.