A discussion about ma'aser in the context of perforated pots - where the perforation is in the land of Israel, but the pot is outside the land. What gives plants their primary nourishment - ground or air? We might have resolved the science of this by today, but they were figuring it all out, still. It becomes a real puzzle when to tithe, but the focus is definitely on the land of Israel. Also, the injunction against writing a divorce on a substance that invites forgery. Which brings us to 3 different stages of tanning animal hides, and each is measured to line up with carrying on Shabbat, and its measures.