Kilayim, Chapter 7, Mishnah 8. This mishnah discusses the status of a pot in which something is growing when it stands in a vineyard, and the distinction between a perforated pot and one that is not perforated.
A perforated pot and an unperforated pot:
"Atzitz nakuv mekadesh ba'kerem" - a pot with a hole in its bottom, filled with earth and with grain growing in it, can bring about a prohibition in the vineyard: whether it is set down in the vineyard itself, or whether it stands within the four amos of vineyard workspace that surround the vineyard. The reason: once it has a hole, it is considered attached to the ground.
"Ve'she'eino nakuv eino mekadesh" - a pot with no hole does not bring about a prohibition, since what grows in it is not considered planted in the vineyard, but rather a separate unit standing on its own.
The view of Rabbi Shimon:
Rabbi Shimon disagrees and holds that there is no difference between the two: whether the pot has a hole or does not have a hole, one may not plant in it at the outset while it stands in a vineyard. Nevertheless, even the perforated pot does not create an actual prohibition, and what grows inside it is not forbidden, even though it has a hole.
Carrying a perforated pot through a vineyard:
The mishnah concludes with a person who carries a perforated pot with a plant growing in it through a vineyard: if the plant in the pot grew by more than one two-hundredth - "Im hosif b'masayim - assur". The vines themselves, however, are not forbidden, since he did not set the pot down on the ground but only carried it through the air.
The words of the Tosafos Yom Tov:
The Tosafos Yom Tov holds that even the prohibition of the grain growing inside the pot, when it grew by more than one two-hundredth, is not a genuine matter of law, but rather a rabbinic enactment imposed as a fine and a penalty. The Sages did not want a person to treat kilei ha'kerem lightly; rather, he should treat it stringently. They therefore said that even carrying the perforated pot through the air creates a prohibition - but again, this is only a fine and a penalty, and not a prohibition by the letter of the law.
In summary: in this mishnah we learned that a perforated pot brings about a prohibition in the vineyard, because it is considered attached to the ground, whereas an unperforated pot is a separate unit and does not bring about a prohibition; Rabbi Shimon holds that in both cases one may not plant at the outset, and that even the perforated pot does not actually forbid; one who carries a perforated pot through a vineyard - the plant becomes forbidden if it grew by more than one two-hundredth, but the vines are not forbidden; and according to the Tosafos Yom Tov, even this prohibition is not a matter of law but a fine instituted by the Sages, so that a person should not come to treat kilei ha'kerem lightly.