On the bottom of 12a Rav Ashi asked how R' Yochanan knew our mishnah was discussing gezeiras otzar and not the issur d'orisah of taaseh v'lo min heh'asoy. The Gemarrah answers that R' Yochanan knew it from the loshon of the mishnah which stated Ein Mesachechin that it was discussing a Rabbinic decree - gezeiras otzar and not a D'orisah level issur.
But, the mishnah on 11a also used Ein Mesachechin and it was discussing there D'orisah issurim.
Avraham Sacks, Ramat Beit Shemesh
Avraham, you are asking Tosfos' question (12b, DH Ein)!
Tosfos answers that the Tana is exacting in his words only when a doubt seems to exist, and therefore the Mishnah is extra careful in his words (like in our Mishnah), but when the reason is clear (like in the Mishnah of 11a) the Mishnah can and will use terms without worrying that it will be misunderstood.
All the best,
Reuven Weiner
Thank you very much for your help and time.
Since the Gemarra asks for the source of not using something that can mikabel tumah and grows from the ground, how is the reason in the Mishnah on 11a clear?
Thank you again for all of your help,
It seems that the Gemara knows that the source is a Pasuk, but is trying to find which Pasuk.
All the best,
Reuven Weiner