Daf Yomi - Sukkah 13 - Colonel Stalks

The Gemara cites one opinion that maintains that if one cuts grain with the intention that it should be used for s’chach, there is a Halacha of yados, i.e. that the grain does have handles, and the stalks can transmit tumah to the kernels. The rationale for this is that there is some benefit from the kernels being attached to the straw, as in this way the kernels will not be scattered and go to waste. Rashi maintains that since the stalks are attached to the kernels, the kernels will not go to waste. Tosfos maintains that the kernels will weigh down the stalks and this will keep the stalks from scattering. The Gemara states further that if one used this grain for s’chach and there is more stalks than kernels, it is valid. Marcheshes raises a difficulty with the opinion of Tosfos, because if the reasoning that the s’chach is valid is because the kernels weigh down the stalks, the s’chach should be invalid as the kernels are susceptible to tumah and the Gemara further on Daf 21b invalidates s’chach that is placed in such a manner. Marcheshes answers that since the stalks are covering the Sukkah without the assistance of the kernels, the s’chach is deemed to be valid. The kernels are merely placed there to ensure that the stalks do not scatter. Thus, we do not deem the s’chach to be held up by the kernels. It is possible that for this reason people are not concerned with inserting screws or nails into the boards that are subsequently attached to the walls of the Sukkah, although in this manner the s’chach is supported by the screws. The reason this would be permitted is because it is the boards that are supporting the s’chach and the screws merely function as a safeguard so the boards do not move from their position.