Peah, Chapter 3, Mishnah 4. This mishnah deals with onions left in the ground in order to produce seed, and with beds of onions growing among other vegetables.
"Habetzalim shehinicham lezera" - the onions that he left for seed:
A person harvested the onions in his field and left some of them in the ground to supply seed. Although the onions that were harvested at the outset were intended for eating and were fully fit for it, those onions left for seed are barely edible. Are they obligated in peah?
Tanna Kamma - "chayavin bepeah" - they are obligated in peah. They can still be eaten, and the first onions taken out of the ground were completely fit for eating.
Rabbi Yosei - "poter" - he exempts them. Since these are not fully fit for eating, and people do not normally eat them, they are not obligated in peah.
"Malbenos habetzalim shebein hayarak" - the beds of onions that are among the vegetables:
The second case: rectangular plots of onions growing in a field, situated among the other vegetables. Is the vegetable growth between them considered an interruption, making each plot a field in its own right?
Rabbi Yosei says: "peah mikol echad ve'echad" - peah from each and every one. The vegetables between the plots interrupt them, and each plot of onions is considered a separate field, so peah must be separated from each one individually.
And the Sages say: "me'echad al hakol" - from one for all of them. The vegetables between them are not considered an interruption, and it is enough to separate one peah from the whole.
Some explain the reasoning of the Sages: the vegetables themselves are not obligated in peah. As has been explained, one of the conditions for the obligation of peah is that the crop be "machniso lekiyum" - something that can be put into storage, and leafy vegetables cannot be stored. Since these vegetables are exempt from peah, we view them as though they do not exist at all, and there is nothing interrupting between the onion plots. Therefore all the plots are considered one field, and one peah is separated from them.
In summary: in this mishnah there is a dispute about onions left for seed - the Tanna Kamma obligates them in peah and Rabbi Yosei exempts them; and about the onion plots among the vegetables - Rabbi Yosei views the vegetables as an interruption and requires peah from each and every plot, while the Sages do not view them as an interruption and require one peah from the whole.