Demai, Chapter Six, Mishnah Nine
In this mishnah two brothers inherit property from their father. The father was an am haaretz, meaning he did not tithe, nor did he preserve the purity of his produce. One of the brothers is a chaver one who tithes and is cautious about the laws of property, while the other is an am haaretz, as was his father. Our mishnah instructs them in how they can split the inheritance. The situation is similar to that in yesterdays mishnah, with regard to the issue of tithes. The added issue here is the matter of purity.
1) A chaver (rabbinic associate) and an am haaretz who inherited [the property of] their father who was an am haaretz, he (the chaver) may say to him (the am haaretz): You take the wheat which is in this place and I will take the wheat which is in that place. Or, You take the wine which is in this place and I will take the wine which is in that place.
2) But he may not say to him: You take the wheat and I will take the barley, or, You take the wine and I will take the oil, or: You take the moist produce and I will take the dry produce.
Section one: This is the same exact rule that we found in yesterdays mishnah. The two can split the produce of the field and we look at it as if each side is getting the portion of the field that he actually inherited. It is not as if the chaver is giving produce to his am haaretz brother.
Section two: In this case, as in yesterdays mishnah, since everyone inherited both wheat and barley, he cant swap one type of grain for another. This type of agreement is treated as if the chaver is giving his portion to his am haaretz brother and it is forbidden to give untithed produce to an am haaretz, because it is known that he will not tithe. We furthermore learn here that swapping the moist produce, produce which has already become susceptible to impurities and is probably impure, with the dry produce which could not have become impure is impossible, because this is considered to be like swapping one species of grain for another. In other words, dry grain and wet grain are treated the same way as are wheat and barley.