Peah, Chapter 6, Mishnah 9. In the previous mishnayos, Mishnah 6 and Mishnah 7, we learned that a sheaf containing two se'ah, and likewise standing grain containing two se'ah, do not become shichechah even if they were forgotten. A quantity that large, whether in a sheaf or in standing grain, is not subject to the law of shichechah.
Our mishnah deals with a case in which two halves of that quantity come together: one se'ah is still attached to the ground, while the other has already been uprooted and harvested. Do these two combine to form the two se'ah measure?
The text of the mishnah:
"Se'ah tevuah akurah u'se'ah she'einah akurah" - one se'ah of grain that has already been harvested and is no longer standing, and an additional se'ah that is still standing and attached. Even though together there is a quantity of two se'ah here, they do not combine: combining standing grain with grain that is not standing is of no effect, and it becomes shichechah.
The same law applies to the other species:
"V'chein ba'ilan" - so too with fruit of a tree, when two of them were forgotten, one attached and one not attached.
"V'hashum v'habetzalim" - garlic and onions follow the same rule.
Regarding all of these the mishnah rules: "Einam mitztarfin lise'asayim" - they do not combine to form the quantity that removes them from the law of shichechah, "ela shel aniyim hein" - and they are therefore shichechah and belong to the poor.
The precise reading of the Rishonim in the name of the Yerushalmi:
The Rishonim raise an important point in the name of the Yerushalmi, based on what we already learned in the previous mishnah, Mishnah 8: standing grain saves. That is, attached grain that was not forgotten has the power to save what was forgotten from becoming shichechah. Therefore, in the case before us - one se'ah attached and one se'ah not attached - the order in which they were forgotten is decisive: if the uprooted grain was forgotten first, it can never become shichechah, since the attached se'ah, which has not yet been forgotten, saves it.
It follows that our mishnah is speaking specifically about one of two situations:
That he forgot both of them at the same time.
That he first forgot the standing grain, and only afterward the uprooted grain. Standing grain saves only when it has not been forgotten, but once it has been forgotten first it no longer has the power to save, and both become shichechah.
In these situations the ruling of the mishnah applies, that the two se'ah are not combined to form the two se'ah measure.
The view of Rabbi Yosei:
The mishnah concludes with a condition added by Rabbi Yosei: the ruling that a sheaf of standing grain is not combined with a sheaf of uprooted grain to form the two se'ah measure applies specifically when there is something belonging to the poor between them - a bit of leket, shichechah or peah separating them. In that case they do not combine, and they are shichechah belonging to the poor. But if there is nothing belonging to the poor between them, they do combine with one another, they are considered a quantity too large to be shichechah, and they remain in the possession of the owner.
In summary: in this mishnah we learned that a se'ah of uprooted grain and a se'ah that is not uprooted do not combine to form the two se'ah measure that removes them from the law of shichechah, and the same applies to a tree, to garlic and to onions - and they belong to the poor. The Rishonim, in the name of the Yerushalmi, understood precisely that this ruling applies specifically when he forgot both of them together, or when he forgot the standing grain first, for otherwise the standing grain would have saved it. And Rabbi Yosei added that they are considered separate only when something belonging to the poor separates between them.