(Mishnah): If one sees a vegetable growing in a vineyard and he says, "When I get there I will pick it" - it is permitted. If he said, "When I will return, I will pick it" - if while he was away it grew 1/200th, it is prohibited.

(Gemara) (R. Yosi bar Chanina): The Mishnah was referring to a worker (but the land owner who was not working must uproot it immediately). (However) if the land owner was working there, he is (also) like a (hired) worker.

If a land owner allowed vegetables to grow in his vineyard, both the vines and the vegetables become prohibited to all.

If a worker allowed vegetables to grow in a vineyard, they are forbidden to him but permitted to everyone else.

Question: If they are forbidden to him they should be forbidden to all; and if they are permitted to everyone else, they should be permitted to him?

Rather, it follows R. Shimon who said that a person cannot prohibit something that is not his. Even though R. Shimon says this, he agrees here that the worker prohibits for himself if he saw it and didn't pick it and then another person picked it; but if he later picked it himself, it is forbidden to all.

The Mishnah taught that if it grew 1/200th it is prohibited. R. Yannai explained that they evaluate it using a Yirvuzah plant. How is it done? R. Baybei said from R. Chanina - he picks one Yirvuzah and leaves another one in the ground and later compares them.