Pesachim, Chapter 2, Mishnah 6. This mishnah deals with the types of vegetables with which one can fulfill the obligation of maror.
"V'eilu yerakos she'adam yotzei bahen y'dei chovaso baPesach" - these are the vegetables with which a person can fulfill his obligation on Pesach, meaning the mitzvah of maror.
The species valid for maror:
It should be noted at the outset that the precise translation of the species listed here is not clear for all of them:
"Bachazeres" - a type of lettuce.
"Uv'ulshin" - endives, according to most understandings.
"Uv'samcha" - some identify this with what is known today as horseradish.
"Uv'charchavina" - a type of thorny plant.
"Uv'maror" - a type of coriander seed.
What all of these species have in common is some form of bitterness.
The condition of the vegetable - what is valid and what is not:
"Yotz'in bahen bein lach uvein yeveshin" - one can fulfill the obligation with them whether they are moist or dry. But there are conditions that disqualify the vegetable:
"Aval lo kevushin" - when they have been soaked in an acidic substance or the like.
"Aval lo shelukin" - sheliкah is, as most commentators understand it, an extreme form of cooking.
"V'lo vishulin" - and not even with ordinary cooking.
In any of these conditions - pickling, over-boiling or cooking - one does not fulfill the obligation with them; whereas when they are moist, and even when they are dry, one can fulfill the mitzvah.
Combining the species, and the stalk:
"U'mitztarfin bik'zayis" - the various types of maror can be combined with one another to make up a kezayis, which is the amount that must be eaten to fulfill the mitzvah.
"V'yotz'in b'kelach shelahen" - not only with the leafy part of these plants, but even with the stalks, the stems, one fulfills the obligation.
The laws of terumos and maasros:
As was taught in the previous mishnah regarding matzah, here too the mishnah lists situations in which one can fulfill the mitzvah:
"Uv'demai" - even with produce purchased from an am ha'aretz from which maasros were not separated, since a poor person is permitted to eat demai.
"U'maaser rishon shenitlah terumaso" - maaser rishon from which terumas maaser was separated. "Aval lo Terumah gedolah" - this refers to a case where it had not yet become obligated in Terumah gedolah.
"U'maaser sheni v'hekdesh shenifdu" - maaser sheni and hekdesh that were redeemed: even if the fifth was not added to them, the redemption is valid and one can fulfill the obligation with them after their redemption, even though they were not redeemed in the complete and proper manner.
It should be added that the Gemara concludes that the words of the mishnah "bein lach uvein yeveshin", according to which one can fulfill the obligation with these types of maror even when they are dry, are said only with regard to the stalk - the stem that the mishnah mentions later - and not with regard to the leaves. Once the leaves have dried out, they are no longer valid as a form of maror, and one does not fulfill the obligation with them.