Demai, Chapter One, Mishnah One
As I explained in the introduction, when one purchases produce from an am haaretz, one must suspect that he did not separate tithes. This produce is called demai. Our mishnah teaches that with regard to certain types of produce the rules of demai dont apply. This is because these things are not important items and are usually left out in the fields for anyone to take. They are ownerless or hefker and anything that is ownerless is exempt from the laws of terumah and tithes in the first place. Therefore, we assume that the am haaretz gathered this produce from ownerless property and hence it was never liable to be tithed.
1) The [following] are treated leniently in regard to [the rules of] demai: unripe figs, wild jujuba, azarolus, wild white figs, young sycamore figs, fallen dates, fennel and capers.
2) In Judea also sumac, Judean vinegar, and coriander.
3) Rabbi Judah says: all unripe figs are exempt, except for those from a tree that bears fruit twice a year. All wild jujuba are exempt, except the wild jujuba of Shikmonah. All young sycamore figs are exempt, except those that have been scarified.
Sections one and two: This is a list of things that are usually left ownerless, as I explained in the introduction above. One who purchases one of these things from an am haaretz need not separate tithes from them. I must confess, I do not know exactly what all these things are.
Section three: Rabbi Judah limits the list found in section one. Unripe figs that come from a tree that bears fruit twice a year are subject to the laws of demai. Evidently, these figs are good, and are not left ownerless. So too the wild jujuba of Shikmonah, a place near Haifa, is good. Finally, young sycamore figs that have been scarified to hasten their ripening are good figs and are not left ownerless.