Kilayim, Chapter Five, Mishnah Five
Our mishnah begins to discuss what happens if seeds are planted in a vineyard. Deuteronomy 22:9 reads, You shall not sow your vineyard with a second kind of seed (kilayim), else the cropfrom the seed you have sownand the yield of the vineyard may not be used (pen tikdash). The rabbis understand the words pen tikdash to mean that one cannot derive any benefit at all from these crops. Furthermore, this prohibition is not just for one who plants kilayim, but also from one who allows kilayim that have already grown to remain in a vineyard.
Our mishnah teaches how much of the vineyard becomes forbidden if kilayim are planted or even found there. The general principle is that the seeds cause all vines within a eight cubit radius (half of what the mishnah refers to as a 16 cubit diameter) to become prohibited.
1) One who plants a vegetable or leaves it to remain in a vineyard, he renders prohibited [as kilayim] forty-five vines.
a) When is this so? When they were planted with either four or five [cubits between rows].
2) If they were planted with either six or seven [cubits between rows] he renders prohibited as kilayim [the vines within an area of] sixteen cubits in every direction, in the form of a circle, not of a square.
Section one: Picture a vineyard where the rows are separated by four cubits. If there are seeds in the middle of such rows and you draw a circle whose radius is 8 cubits around this point, it will turn out that 45 vines are within this radius (Im sorry, but I dont think I can draw this one). Therefore, all 45 vines are prohibited. If there are five cubits between each row, then only 37 vines will be within the circle. However, the mishnah still rules that 45 vines are prohibited because a person might make an error between four and five cubits.
Section two: However, if there are more than four or five cubits between the rows, lets say that there are six or seven cubits, then we simply draw a circle whose radius is 8 cubits around the seeds and any vine which falls in this radius is prohibited.