Challah, Chapter 1, Mishnah 2. This mishnah continues the discussion of the five species of grain - wheat, barley, spelt, oats and rye - this time with regard to additional laws beyond the laws of challah.
The laws of matzah and chametz on Pesach:
"Ha'ochel meihem k'zayis matzah b'Pesach - yatza y'dei chovaso" - one who eats a k'zayis of matzah made from one of these five species has fulfilled his obligation to eat matzah. The source of this law is the juxtaposition of the passages in the book of Devarim, where the prohibition of eating chametz is placed alongside the mitzvah of eating matzah. From here we learn that the species that can become chametz are the species with which one can fulfill the mitzvah of matzah. These five species are the only ones that become leavened, whereas the other kinds of produce do not become leavened at all but merely rot.
"K'zayis chametz - chayav b'kareis" - one who eats a k'zayis of chametz from one of these five species is liable to kareis, which is the punishment for eating chametz on Pesach.
"Eirav echad meihem b'chol haminim - harei zeh over b'Pesach" - if one of the five species of grain that became chametz was mixed into the other species, two explanations were offered for the expression "over b'Pesach" (transgresses on Pesach):
Some explain that one who keeps a mixture containing chametz transgresses "bal yeira'eh" and "bal yimatzei" (it shall not be seen and it shall not be found).
Others explain that the mishnah means that there is an obligation to destroy the mixture and eliminate it from the world.
Either way, such a mixture is forbidden on Pesach.
The laws of vows:
"Hanoder min hapas umin hatevuah - asur bahem, divrei Rabbi Meir" - one who vows not to eat bread or produce is forbidden to eat these five species. According to Rabbi Meir, these species are what constitute the category of tevuah, grain. However, the term "dagan" in the Hebrew language may include even species beyond the five species of grain, since it includes anything that is piled into a heap.
"V'chachamim omrim: hanoder min hadagan eino asur ela meihen" - the Sages disagree and hold that even one who vows using the term "dagan" is forbidden only in the five species. All the other species - rice, corn and the like - are not considered dagan.
Challah and tithes:
"V'chayavim b'challah uv'maasros" - the five species are obligated in the separation of challah and in the separation of tithes. The obligation of challah was already mentioned above, and the obligation of tithes was mentioned at the beginning of the first mishnah, and the repetition here serves as an introduction to the next mishnah, which will discuss which items are obligated in challah but possibly not obligated in tithes.
In summary: in this mishnah we learned the laws of the five species of grain beyond challah: one fulfills the obligation of matzah on Pesach with them, and one is liable to kareis for eating a k'zayis of chametz from them; a mixture containing them is forbidden on Pesach, whether because of "bal yeira'eh and bal yimatzei" or because of the obligation to destroy it; with regard to vows, Rabbi Meir and the Sages disagree about the scope of the term "dagan"; and finally we learned that these species are obligated in challah and in tithes, as an introduction to the discussion in the next mishnah.