Kilayim, Chapter 6, Mishnah 3. Our Mishnah deals with training a vine, that is, attaching it to a structure or a tree so that it will take hold and continue to grow along it. The question is the status of the area beneath that structure at a time when the vine has not yet spread across all of it.
"HaMadleh es hagefen al miktzas apifiyros": - one who trains a vine over part of a trellis.
An apifiyros is a latticework frame, designed from the outset for vines to grow within it and spread along its length. The Mishnah discusses someone who trained his vine over only part of the trellis, and rules: "Lo yavi zera el tachas hamutar" - he may not bring seed beneath the remaining portion, even in the area where the vine is not yet found. The reason: since the entire frame is set aside and designated for the vine to grow upon it, sowing is forbidden beneath all of it.
"Im heivi - lo kidesh": - if he did bring seed there, he has not rendered it forbidden.
Even though it is forbidden to do this at the outset, if he actually sowed there, "lo kidesh" - the seeds are not forbidden and this is not kilei hakerem. The prohibition to sow is only a warning against doing so at the outset, since at that stage there is no actual vine above that part of the frame.
However, "im halach hachadash - asar" - once the new growth of the vine spreads and grows above the area where the seeds were sown, they become forbidden as kilei hakerem, for now there is an actual vine growing above them.
"Vechen hamadleh al miktzas ilan srak": - and so too one who trains a vine over part of a barren tree.
This law is not limited to a trellis structure; it applies as well to someone who trained his vine over part of a barren tree, a tree that does not produce fruit. The distinction between the two cases:
A barren tree: its status is like that of a trellis, because a person is not particular about a tree that bears no fruit, and it is even convenient for him that the vine should spread and grow along it.
A fruit tree: a person does not allow a vine to grow upon it, and therefore its status is not like that of a trellis, as we will see in the next Mishnah.
In summary: one who trains a vine over part of a trellis may not sow even beneath the empty portion, since the whole of it is designated for the vine's growth; and if he did sow, he has not rendered the seeds forbidden, so long as there is no vine above them. Once the new growth of the vine has spread above them, it renders them forbidden. This law applies as well to a barren tree, upon which a person is not particular about the vine's growth, but not to a fruit tree.
In the next Mishnah we will deal with the law of one who trains a vine over part of a fruit tree, and with the difference between a barren tree and a tree that produces fruit.