Kilayim, Chapter Four, Mishnah Three
In todays mishnah Rabbi Judah disagrees with the definition of a mehol found in yesterdays mishnah.
1) Rabbi Judah says: this is nothing but the fence of the vineyard fence.
2) What then is a mehol of a vineyard? [A space] between two vineyards.
3) What is considered a fence? One that is ten handbreadths high.
4) And what is considered a trench? One ten handbreadths deep and four wide.
Section one: Rabbi Judah says that the empty space between a fence and a vineyard is not a mehol but is rather considered an extension of the fence. In such an area it is prohibited to sow seeds, even if the area is more than twelve cubits by twelve cubits.
Section two: According to Rabbi Judah a mehol is the empty space between two vineyards. If there are twelve cubits of such space, they leave four cubits on each side in which to work the vineyard and there will be four cubits left in the middle in which he can plant seed.
Section three: For a fence to legally separate two different entities it must be ten handbreadths high. Note that this was the same height as the eruv and the sukkah. Anything under ten handbreadths is too small to be considered.
Section four: Similarly, when areas are separated by trenches, the trenches must be ten handbreadths deep in order to function as legal separators (this was already taught above in 2:8).