'HANDS' OF TUMAH (Yerushalmi Halachah 6 Daf 6a)
חיננא בר שלמיה בשם רב קצר לסכך אין להן ידות
Chinana bar Shalmei quoting Rav: If one cut wheat for Schach, it does not have 'hands'. (If a Tameh item touched the straw, the straw is not a 'hand' and therefore it does not transfer the Tumah onto the seeds.)
קצר לסכך וחישב עליהן למאכל בא במחשבה
If one cut wheat for Schach and later decided to use it as food, his decision causes it to be able to contract Tumah (i.e. the straw becomes a 'hand').
קצר למאכל וחישב עליהן לסכך אחרי' אומר[ים] עד שיהא הקש רבה על האוכל ועל היד
If one cut wheat for food and later decided to use it as Schach - Acheyrim say that the straw (valid Schach) must outnumber the food and the 'hand' (as they are both invalid Schach).
רב כהדא דאחרים
Rav can even follow Acheyrim (even though Rav holds that thought caused these 'hands' to become susceptible to Tumah and Acheyrim hold that thought cannot remove the Tumah status from 'hands').....
מה אנן קיימין קצר לסכך והוכשרו ואמר לכשיעשו מצותן אחזירם לגורן
What is the case? He cut the wheat as Schach and it became Huchshar; he then said, "once their Mitzvah has been done, I will return them to the threshing floor (to be used as food)".
צריכין הכשר פעם שנייה או כבר הכשירן בידם
Query: Would they need to get wet again after he returned them to the threshing floor, since at the time of Hechsher they were not susceptible to Tumah; or do we say that since at the time of their original Hechsher he had been planning on returning them to the threshing floor, so they do not need to get wet again? (This question remains unanswered.)
רבי יסא בשם רבי חמא בר חנינה (שמות מ) וסכת על הארן את הפרוכת. מיכן שהדופן קרוי סכך
R. Yasa quoting R. Chama bar Chanina: The Pasuk states (Shemos 40, 3), "(Vesachosa) And you shall screen the Aron with the curtain" - we learn from here that a wall can be referred to as Schach; so why may the walls be constructed from materials that are susceptible to Tumah?
מיכן שעושין דפנות בדבר שהוא מקבל טומאה
Answer: If we are learning from the curtain in the Mishkan, since we find that the curtain was susceptible to Tumah, the walls of a Sukah may also be susceptible to Tumah. (Note: This entry follows the explanation of the Pnei Moshe.)