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1. The Gemara discusses the source for the limitations on Sechach, such as the requirements that it cannot become Tamei and that it must grow from the ground.
2. The Gemara says that one may not use bundles of branches for Sechach.
3. The Gemara discusses the reasoning of "Gezeiras Otzar," "the decree of the storehouse."
4. The Gemara discusses the teaching, "Ta'aseh v'Lo Min ha'Asuy."
5. There is a dispute about whether one may use various items that grow from the ground as Sechach.
A BIT MORE
1. For example, Rav Chisda derives this requirement from the verse in Ezra that instructs Bnei Yisrael to make Sukos from the leaves (and branches) of different plants.
2. However, if the bundles are untied, then their contents may be used as Sechach. The bundles also may be used as walls without untying them.
3. A person might place a bundle of wood on top of his Sukah to store it there and end up sleeping under it. Since the wood was not placed there for the purpose of Sechach (to create shade below), the Sukah is invalid and he does not fulfill the Mitzvah.
4. This means that Sechach must be specifically made to create shade, and one must perform an action with this intent when he places the Sechach on the Sukah. Accordingly, if a person burrows through a haystack and creates a space valid for the area of a Sukah, the Sukah is invalid since he did not do a positive action to make the Sechach (rather, it came about passively).
5. For example, Rav Yehudah says that one may use a certain growth used as animal food called "Shivtzeri" as Sechach. Abaye says that one may not use it as Sechach because its putrid smell will cause a person to leave the Sukah.
Next Daf Index to Revach for Maseches Sukah