Uktzin, Chapter 2, Mishnah 10. This mishnah continues the discussion of produce growing in planters, and teaches that some vessels are treated as porous even when no hole was ever made in them.
The Background: Two Kinds of Planter
A brief reminder of a principle we know from earlier masechtos. An atzitz nakuv, a planter with holes, is regarded as joined to the earth, so whatever grows in it is mechubar lakarka and cannot receive tumah. An atzitz she'eino nakuv, a planter with no holes, is talush, detached, and produce inside it can indeed become tamei.
Vessels That Are Porous by Nature
The Mishnah opens: "Klei gelalim", vessels formed from hardened animal dung, "uchlei adamah", and vessels of earth that were never fired in a hot kiln, "shehashorashim yecholin latzeis bahen", in which roots are able to make their way out through the walls. Anyone who plants in such a container sees it: the roots begin to work their way through the sides.
Of such vessels the Mishnah rules: "einam machshirin es hazera'im", they do not bring the seeds planted in them to the state of hechsher. And this holds true even if, in this particular case, no root has actually broken through the wall. The very fact that a root could pass through demonstrates that the vessel is porous, and a porous vessel has the standing of an atzitz nakuv. Whatever grows in it is therefore considered attached to the ground.
The Pot With a Hole
The Mishnah continues: "atzitz nakuv eino machshir es hazera'im", a planter with a hole does not enable the seeds growing in it to become tamei. Since the pot is treated as one with the earth beneath it, what grows there is attached to the ground, and attached produce is beyond the reach of tumah.
Water in Such a Pot
One more matter deserves attention here, and it concerns the water. When water is still bound up with the earth and has not been detached from it, talush min hakarka, as with water that has collected in a hollow dug into the ground, it has no power as machshir zera'im: it will not make produce liable to tumah. Water sitting inside an atzitz nakuv is judged the same way. Since the pierced planter itself carries the status of the earth, whatever water stands in it is no different from water lying in a hole in the field, and it likewise fails to function as machshir zera'im.
The lesson of the mishnah, then, is that the halachah looks at what a vessel truly is. A dung vessel or an unfired earthen vessel may show no hole to the eye, yet because roots pass through it freely, it belongs together with the pierced planter and its produce remains bound to the ground.