Question: We have only learned that rows of Mukshos must be distanced 8 Amos when they are planted densely in the row - but what about when single ones are planted at a distance from each other?

Answer: Just as for a vineyard, there's no difference whether the vines are dense or at a distance from each other, so too here.

(R. Yannai): (The Mishnah taught (above in Menachos 51(b)) that if there's one row of squash, one row of pumpkin, one row of Egyptian bean and then another row of squash - R. Eliezer permits it and the Chachamim prohibit it.) They (also) disagree over (the middle case of the Mishnah, where there are 3 single rows of different species) - whether two species can combine to save (themselves) but don't combine to prohibit a third species.

(Rav disagrees): All agree in the middle case that just as two species combine to save, so too they combine to prohibit a third species.

Question (Our Mishnah against R. Yannai): (In the third case) R. Eliezer permits (which implies that he does not disagree and permit the second case)...?

Question (Our Mishnah against Rav): (The third case taught that) if there's one row of squash, one row of pumpkin, one row of Egyptian bean and then another row of squash (R. Eliezer permits it). (How could R. Eliezer permit it if) before the fourth row was planted it had already become prohibited?

Answer: All four were planted at the same time.

The last case of the Mishnah taught that a person may plant squash (and gourd in the same hole, as long as each one bends in its own direction). A Baraisa taught that a person may make a small pit in his field a Tefach deep, plant four types of seeds in it and turn them each in a different direction.

(R. Abba bar Kahana/ Shimon Grashaya citing R. Shimon ben Lakish): They must be turned towards an empty area.

Question (R. Mana): If so, it should permit planting eight different species - one in each corner (facing diagonally away) and one in the middle of each side. (The Gemara leaves this question unanswered.)