Before us is Mishnah 4 in the second chapter of Maseches Challah, which deals with the joining together of separate batches of dough and loaves of bread to make up the measure that obligates one to separate challah.
"Oseh isaso kabbim":
This speaks of a person who makes his dough in small quantities, one kav at a time. As we learned in the previous Mishnah, the measure that obligates challah is five quarters of a kav, that is, a kav and a quarter. Therefore a dough of only one kav is not subject to the laws of challah - it does not contain the required measure, and there is not enough there to create an obligation to separate challah.
And what is the law regarding several separate batches of dough, each one the size of a kav, that are touching one another? The Mishnah rules: "Nog'os zu ba'zu - peturos min ha'challah, ad she'yishoichu" - if they are touching one another they are exempt from challah until they stick to one another. As long as they are merely touching, each one is still exempt from the mitzvah of challah. The obligation takes effect only once they stick together, that is, when they come so close and become so attached to one another that when they are pulled apart each one takes a piece of the other, and they do not separate cleanly, but part of the one dough comes away with the other. The term 'yishoichu' derives from the word for biting, since each one bites off a piece of its fellow. From the moment they are joined in this way, they are considered attached, and the required measure is present.
Rabbi Eliezer's view - the basket combines:
Rabbi Eliezer adds that not only sticking together creates a combination, but the basket does as well: "Ha'rodeh v'nosen la'sal - ha'sal metzaref la'challah" - one who removes the loaves and places them in the basket, the basket combines them for challah. 'Rodeh' means taking the bread out of the oven after it has been baked, and when he places it into the basket, the basket itself helps to join the various loaves of bread to one another to create the obligation of challah.
Although the time for separating challah is already from the moment the dough is made, nevertheless, if in practice he did not separate it at the proper time from the dough, he is still obligated to separate challah from the bread itself after it has been baked. According to Rabbi Eliezer, the loaves can be joined to one another by placing them together in a basket: the basket combines them to make up the measure that obligates challah, and at that point he separates challah from them.