Tosefta su Pe'ah 4:12

The gleanings and the forgotten sheaves and the peah [taken from the field] of a Gentile are liable in tithes (see Peah 4:9, "unless he declared them ownerless"). When is this? At a time that the Gentile protests [his produce being deemed ownerless, thus rendering it liable for tithes (see Kulp at Peah 4:9)], but if the Gentile does not protest [and consents to his property being deemed ownerless], the ownerless property of a Gentile is [indeed] ownerless, and exempt from tithes.

An ear of grain that is among the standing grain, behold, it belongs to the homeowner. [An ear of grain] that is among the harvested [grain], behold, it belongs to the poor. [If] half is among the standing grain, and half is among the harvested [grain], he takes it and throws it behind him, because [in a case of] doubt [as to what is considered] gleanings, [the doubt is resolved in favor of its status being] gleanings (see also Peah 6:4 re: forgotten sheaves).

[With respect to grain found in] ant holes (see Peah 4:11), it is forbidden [to the poor] under [the laws of] stealing, but if the homeowner declared them ownerless, they are permitted [under the laws of] stealing [and thus, the poor may take them]. Rabbi Shimon ben Elazar says, "If they were [intentionally] stored there, they are forbidden under [the laws of] stealing."

One who declares his orchard ownerless (see Peah 4:9), the rich people [may] take away the grapefruits and the grapes, [and] the poor people [may] take away the grapefruits and the grapes with defective clusters (olelot). What are defective clusters? Any [cluster] that lacks a "shoulder" or a "pendant." If it has a shoulder but not a pendant, or has a pendant but lacks a shoulder, behold, it belongs to the property owner, and if not, behold, it belongs to the poor people. What is a "shoulder"? Growths joined to each other at the stem, each one next to the other (and see Bartenura to Peah 7:4). What is a "pendant"?Grapes joined to the stem that drop down (and see ibid.).

[In the case of] one who gives his field for [for purposes of] being sharecropped by a Samaritan or a Gentile (following Erfurt, but see GR"A, striking "or a Gentile"), or to someone who is not trustworthy as to tithes, even though he is not permitted to do so, even though [the produce is still premature and] not yet subject to tithes (see Peah 4:8), he needs to tithe it himself when it [ripens and] becomes subject to tithes. [In the case of] one who gives his field for [purposes of] being sharecropped by an am ha'aretz, until the time that [the produce] becomes subject to tithes, he needs to (but see GR"A, "he does not need to") tithe it himself, [and] when it does become subject to tithes, there is no need for him to (but see GR"A, "he needs to") tithe it himself. How [does he do this]? He stands on the threshing floor, and takes [the tithes]. And we are not concerned that someone may have eaten [some of the produce before it reached the threshing floor], as we are not responsible for deceivers.