(Mishnah): One who is Mavrich a vine (reinserts the attached branch of a vine into the ground to then protrude elsewhere with renewed growth) - if there aren't three Tefachim of earth on top of it, he shouldn't introduce there another seed, even inside a (hollowed out) gourd or in a pipe.

If he was Mavrich it into a rock, even if there are only three fingerbreadths on top of it, it is permitted to bring another seed.

A bent vine in a vineyard is measured from the second root (since it appears to be planted from there).

(Gemara): The Mishnah taught, "...he shouldn't introduce there another seed'' - but from the side is permitted.

What's the case? If the problem is that the seed roots enter into the place of the vine roots, why talk specifically about a vine? If it's because he's planting within the work access area of a vine, let it teach 6 Tefachim?

Rather, it follows R. Akiva, who said that only 3 Tefachim must be distanced from a single vine.

Rebuttal: If so, it should be prohibited even from the side and it should just teach three Tefachim (without mentioning 'on top of it')?

Answer (R. Yirmiyah citing R. Chiya bar Abba): (It's not because of work access; rather) it's prohibited because roots of seeds may not be planted on top of a vine.

(Mishnah in Maseches Bava Basra): One must distance seeds, a plow and urine three Tefachim from a (neighbor's) wall (as they damage it).

Question: Our Mishnah implies that seed roots do not spread out sideways and the Mishnah there says that they do?

Answer (R. Yosi): The concern of that Mishnah is that the roots cause the soil to become crumbly thereby weakening the wall. This is certainly true as urine itself doesn't move sideways.

Question (R. Yosi bei R. Bun): (Perhaps one could think that urine could spray sideways) but the Mishnah also taught about a plow - could one suggest that a plow itself moves sideways? So the concern of the Mishnah must be the crumbling of the soil.